Name: antimicrobial characterization of advanced materials for bioengineering applications
Uploaded: 2018-08-04T14:00:00.000+00:00
Duration: 8 min 8 s
Description: Watch this Scientific Journal Video about Antimicrobial Characterization of Advanced Materials for Bioengineering Applications at JoVE.com

The authors would like to acknowledge the Universidad Cat&#243;lica de Valencia San Vicente M&#225;rtir for the financial support for this work through the 2017-231-001UCV and 2018-231-001UCV grants.

1. Sample Preparation
<ol>
	<li>Cut the material samples into 10 mm diameter disks with a 10 mm diameter cylindrical punch. 
	NOTE: Brittle materials can be softened in suitable sterile solvents for 1 h and then cut into disks. For example, hydrophilic materials such as zinc alginate were tested following this protocol and were moistened in autoclaved water before cutting them in order to avoid sample breaking. However, other hydrophobic materials such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) do not need any kind of previous swelling in order to be properly cut.</li>
	<li>Dry the sample material disks at 60 &#176;C in a vacuum oven (&#60;10-2 Torr) for 24 h. 
	NOTE: Some materials may need a high drying temperature. However, it is important not to reach a temperature that could thermally degrade the material.</li>
	<li>Measure the material film thicknesses with a digital caliper. 
	NOTE: This protocol recommends the utilization of material films with constant and similar thicknesses when comparing the antimicrobial activity of different materials.</li>
	<li>Sterilize each specimen&#160;by immersion in&#160;ethanol 70% for 10 min and subsequent ultraviolet (UV) radiation for 1 h per each side. 
	NOTE: UV radiation can be performed placing each specimen in a sterile Petri dish inside a&#160;laminar flow hood with a 12.0 W lamp of UV-C radiation. 
	CAUTION: Researchers should not expose themselves to UV radiation, because it is mutagenic.</li>
	<li>Perform steps 1.1, 1.2, 1.3 and 1.4. with the control material disks.&#160; 
	NOTE: Polyethylene terephthalate (PET) or alternative non-antimicrobial materials could be used as control disks in the diffusion and contact method. Furthermore, when characterizing nanocomposites or treated materials, the base material should be used as control material.</li>
</ol>
2. Recommended Microorganisms
NOTE: We recommend the use of 3 different microorganisms to study the antimicrobial capacity of the tested material against a wide range of microorganisms.
<ol>
	<li>Use pure cultures of 3 microorganisms: the Gram-positive bacteria Staphylococcus aureus, the Gram-negative bacteria Escherichia coli, and the yeast Candida albicans. 
	NOTE: Other microorganism species can also be tested with this protocol by modifying the incubation conditions if necessary. 
	CAUTION: The required biosafety measurements must be followed according to the type of microorganism employed in this protocol.</li>
	<li>Work with pre-sterile or autoclaved material and use a Bunsen burner during the whole process of the microbial manipulation or a biological safety cabinet (if necessary) to ensure aseptic conditions. 
	NOTE: Recommended autoclave conditions are 121 &#176;C during 15 min for culture mediums and 121 &#176;C during 20 min for the working material and biological residues.</li>
</ol>
3. Agar Disk Diffusion Test (Diffusion Method)
NOTE: When a liquid diffusion of antimicrobial compounds might be the main antimicrobial mechanism of advanced materials, the diffusion method can provide very useful information about the antimicrobial capacity of these materials. The material disk located at the center of the agar plate can form a transparent ring zone (halo) where a growth inhibition of microorganisms occurs after 24 h of culture (see Figure 1).
<ol>
	<li>Diffusion test procedure
	<ol>
		<li>Prepare and autoclave tryptic soy agar (TSA) following the manufacturer&#8217;s instructions.</li>
		<li>Pour the TSA into sterile Petri dishes under aseptic conditions using a Bunsen burner or a laminar flow hood. 
		NOTE: The TSA plates must be 4&#8211;6 mm thick.</li>
		<li>Culture the different microorganisms to be tested aerobically for 18&#8211;24 h in the Petri dishes with TSA in an incubator at 37 &#176;C.</li>
		<li>Prepare and autoclave tryptic soy broth (TSB) following the manufacturer&#8217;s instructions.</li>
		<li>Pour the TSB in a 50 mL pre-sterilized centrifuge tube with a pre-sterilized serological pipette under aseptic conditions using a Bunsen burner or a laminar flow hood.</li>
		<li>Resuspend a few colonies from step 3.1.3 in 25 mL of TSB contained in a sterile centrifuge tube using a sterile cotton swab and vortex them for 1 min to achieve a uniform mixing.</li>
		<li>Adjust the absorbance (at 540 nm) of the culture with a spectrophotometer to the suitable number of colony forming units (CFU) per mL: approximately 1.5 x 108 CFU/mL for bacteria and from 1 x 106 to 5 x 106 CFU/mL for yeast. 
		NOTE: The culture and cuvette volumes to measure the absorbance must be selected according to the type of spectrophotometer utilized.</li>
		<li>Vortex the microbial broth for 5 seconds to improve the microorganism dispersion and briefly submerge a sterile cotton swab in this microbial suspension. Remove the excess of liquid from the swab by pressing it against the tube wall containing the culture.</li>
		<li>Evenly streak the microbial broth suspension with the sterile cotton swab onto the surface of the TSA plates in 3 planes to cover their whole surface with the microorganism and let it dry for 5 min after the inoculation. 
		NOTE: To remove any moisture, the TSA plates must be placed open in an inverted position at 37 &#176;C for 10&#8211;15 min before the inoculation.</li>
		<li>Sterilize a pair of tweezers by immersing them in a beaker with ethanol 96% and then flaming them with a Bunsen burner or alcohol burner.</li>
		<li>Place the sample disks to be tested and control disk at the center of the TSA plates using the pair of sterile tweezers.</li>
		<li>Incubate aerobically the TSA plates in an inverted position at 37 &#176;C for 24 h. 
		NOTE: In order to avoid any contamination risk, it is recommended to incubate the TSA plates in an inverted position. However, if the sample disk detaches from the TSA plates, do not perform this step in an inverted position. In this case, it is recommended to dry the plates in the laminar flow hood.&#160;This antimicrobial test must be performed at least in quadriplicate on different days to ensure reproducibility.</li>
	</ol>
	</li>
	<li>Checking of microbial suspension concentration and purity 
	NOTE: The following steps are necessary in order to check that the microbial concentration determined with the spectrophotometer in step 3.1.7 is correct and ensure that there was no microbial environmental contamination. A microbial environmental contamination can be easily detected by the appearance of various types of microbial colonies after 24 h of culture. Furthermore, no microbial contamination of the TSB medium during its manipulation in the decimal serial dilutions must be ensured with a negative TSB control plate.
	<ol>
		<li>Dispense the sterile TSB (prepared in step 3.1.4) into sterile microcentrifuge tubes using a micropipette with suitable autoclaved tips in aseptic conditions. One of them will be utilized as a negative TSB control.</li>
		<li>Perform decimal serial dilutions with the microbial broth suspension utilized in step 3.1.9 in the sterile microcentrifuge tubes containing TSB.</li>
		<li>Spread 100 &#181;L of each dilution on TSA plates using a pre-sterilized Drigalski spatula or an alternative instrument. Also spread 100 &#956;L of TSB medium without microorganism (prepared in step 3.2.1) on a TSA plate as a negative TSB control plate.</li>
		<li>Incubate aerobically the TSA plates aerobically at 37 &#176;C for 24 h.</li>
		<li>Count the number of colonies to check that the CFU/mL are similar to that determined in step 3.1.7.</li>
		<li>Check that there is no microbial environmental contamination on the TSA plates with only one type of colonies.</li>
		<li>Check that there is no microbial contamination on the TSB negative control plate showing no colonies</li>
	</ol>
	</li>
</ol>
4. Measurement of Antimicrobial Activity on Material Surfaces (Contact Method)
 
NOTE: When surface contact might be the main antimicrobial mechanism of some advanced materials, the contact method can provide very useful information about the antimicrobial capacity of these materials. In this method, the microorganisms are placed directly onto the material surface and their growth inhibition can be determined after a certain amount of time.
<ol>
	<li>Initial procedure
	<ol>
		<li>Prepare and autoclave TSB following the manufacturer&#8217;s instructions.</li>
		<li>Pour the TSB in a 50 mL pre-sterilized centrifuge tube with a pre-sterilized serological pipette under aseptic conditions using a Bunsen burner or a laminar flow hood.</li>
		<li>Culture the different microorganisms to be tested aerobically overnight in the tube with TSB in an orbital shaker (140 rpm) at 37 &#176;C.</li>
		<li>Dilute the overnight culture in 20 mL of TSB in a 50 mL pre-sterilized centrifuge tube to a concentration of approximately 106 CFU/mL (determined with a spectrophotometer at 540 nm). 
		NOTE: The culture and cuvette volumes to measure the absorbance must be selected according to the type of spectrophotometer utilized.</li>
		<li>Perform decimal serial dilutions of this culture in sterile microcentrifuge tubes containing TSB. Spread 100 &#181;L of the culture on TSA plates and incubate it aerobically at 37 &#176;C for 24 h.&#160;</li>
		<li>Count the number of colonies to ensure an initial cell concentration of approximately 1 x 106 CFU/mL</li>
		<li>Place 4 control disks for microbial counting after 24 h and 4 sample disks of each type of the tested materials for microbial counting after 24 h in separates wells of a sterile 48-well plate.</li>
		<li>Pipette 150 &#181;L of the microbial suspension onto each disk surface.</li>
	</ol>
	</li>
	<li>Microbial counting on the control and tested materials (after 24 h)
	<ol>
		<li>After step 4.1.6, aerobically incubate the 4 sample disks remaining in the 48-well plate at 37 &#176;C for 24 h. 
		NOTE: This 24 h incubation time can be modified in order to study the growth inhibition at shorter or longer times.</li>
		<li>After 24 h of incubation, pipette 850 &#181;L of sterile PBS onto the surface of the 4 sample disks and mix it with the 150 &#181;L of the microbial suspension.</li>
		<li>Collect the PBS/microbial suspension mixture and each disk from the 48-well plate and transfer them to a 10 mL pre-sterilized tube.</li>
		<li>Vortex the PBS/microbial suspension mixture and each disk&#160;for 1 min, sonicate it&#160;at 50 Hz for 5 min and vortex it&#160;again for 1 min to ensure that no viable microorganisms remain adhered to the material surface.</li>
		<li>Perform decimal serial dilutions of each&#160;sonicated culture in sterile microcentrifuge tubes containing TSB and spread 100 &#181;L of the culture on TSA plates and incubate it aerobically at 37 &#176;C for 24 h.</li>
		<li>Count the number of colonies, which are the number of viable microorganisms on each&#160;sample and control disk surface. Express this number of viable cells in (CFU/mL).</li>
		<li>Take a photograph of the final microbial culture for the sample and control disks.</li>
	</ol>
	</li>
</ol>
5. Antimicrobial Results Analysis
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57710/57710fig1.jpg" /> 
Figure 1: Measurements for the normalized width of the antimicrobial &#34;halo&#34;. This panel shows the diameter of the inhibition zone (diz) and the&#160;disk diameter (d). <a href="/files/ftp_upload/57710/57710fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol>
	<li>Diffusion method results analysis 
	<ol>
		<li>Measure the diameter of the inhibition zone (diz) and the&#160;disk diameter (d) (see Figure 1) with a digital caliper. 
		NOTE: The inhibition zone or antimicrobial &#8220;halo&#8221; is formed as a consequence of the microbial growth inhibition produced by the antimicrobial material disk (see Figure 1). It is possible to observe that there is a transparent ring zone close to the sample in comparison with the rest of the plate where the microorganisms have grown properly (opaque zone).</li>
		<li>Determine the normalized width of the antimicrobial &#8220;halo&#8221; (nwhalo) of each disk&#160;by applying equation (1). 
		(1)&#160;&#160;&#160;&#160;&#160;<img alt="Equation 1" src="/files/ftp_upload/57710/57710eq1.jpg" /></li>
		<li>Determine the mean and standard deviation of the normalized width of the antimicrobial &#8220;halo&#8221; with the 4&#160;determined nwhalo values of each sample.</li>
		<li>Take a photograph of the final microbial culture with the material&#160;disk. 
		Note: The diameter of the inhibition zone (diz) and the disk diameter (d) can also be measured from the photograph taken in step 5.1.4 by using a suitable image processing software.</li>
	</ol>
	</li>
	<li>Contact method results analysis
	<ol>
		<li>Determine the number of viable microorganisms recovered according to equation (2). 
		(2)&#160;&#160;&#160;&#160;&#160;<img alt="Equation 2" src="/files/ftp_upload/57710/57710eq2.jpg" /> 
		NOTE: Here, N is the number of viable microorganisms recovered per cm2 per test specimen; C is the plate count; D is the dilution factor; A is the surface area of the test specimen in cm2 determined with the sample disk diameter.</li>
		<li>Determine the loss of viability (LV) to reflect the inhibition of cell growth by applying equation (3). 
		(3)&#160;&#160;&#160;&#160;&#160;<img alt="Equation 3" src="/files/ftp_upload/57710/57710eq3v3.jpg" /> 
		NOTE: Here, C&#160;is the average number of viable microorganisms (N) in CFU/mL&#8226;cm2, recovered from the control specimens after 24 h; S&#160;is the number of viable microorganisms (N) in CFU/mL&#8226;cm2, recovered from the test specimens after 24 h.</li>
		<li>Determine the mean and standard deviation of the loss of viability with the 4 determined LV(%) values of each sample.</li>
	</ol>
	</li>
</ol>

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L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macroporous+poly(methyl+methacrylate)+produced+by+phase+separation+during+polymerisation+in+solution.">Macroporous poly(methyl methacrylate) produced by phase separation during polymerisation in solution.</a> Colloid Polym Sci. 285 (7), 753-760 (2007).</li><li>Serrano-Aroca, &. #. 1. 9. 3. ;., Llorens-G&#225;mez, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+mechanical+analysis+and+water+vapour+sorption+of+highly+porous+poly(methyl+methacrylate).">Dynamic mechanical analysis and water vapour sorption of highly porous poly(methyl methacrylate).</a> Polymer (Guildf). 125, 58-65 (2017).</li><li>Serrano-Aroca, &. #. 1. 9. 3. ;., Campillo-Fern&#225;ndez, A. J., G&#243;mez-Ribelles, J. L., Monle&#243;n-Pradas, M., Gallego-Ferrer, G., Pissis, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Porous+poly(2-hydroxyethyl+acrylate)+hydrogels+prepared+by+radical+polymerisation+with+methanol+as+diluent.">Porous poly(2-hydroxyethyl acrylate) hydrogels prepared by radical polymerisation with methanol as diluent.</a> Polymer (Guildf). 45 (26), 8949-8955 (2004).</li><li>Rodr&#237;guez-Hern&#225;ndez, J. C., Serrano-Aroca, &. #. 1. 9. 3. ;., G&#243;mez-Ribelles, J. L., Monle&#243;n-Pradas, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+nanocomposite+scaffolds+with+ordered+cylindrical+orthogonal+pores.">Three-dimensional nanocomposite scaffolds with ordered cylindrical orthogonal pores.</a> J Biomed Mater Res - Part B: Appl Biomater. 84 (2), 541-549 (2008).</li><li>Br&#237;gido-Diego, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acrylic+scaffolds+with+interconnected+spherical+pores+and+controlled+hydrophilicity+for+tissue+engineering.">Acrylic scaffolds with interconnected spherical pores and controlled hydrophilicity for tissue engineering.</a> J Mater Sci Mater Med. 40 (18), 4881-4887 (2005).</li><li>Serrano-Aroca, &. #. 1. 9. 3. ;., Ruiz-Pividal, J. F., Llorens-G&#225;mez, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+water+diffusion+and+compression+performance+of+crosslinked+alginate+with+a+minuscule+amount+of+graphene+oxide.">Enhancement of water diffusion and compression performance of crosslinked alginate with a minuscule amount of graphene oxide.</a> Sci Rep. 7, 11684 (2017).</li><li>Serrano-Aroca, &. #. 1. 9. 3. ;., Deb, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+irregular+graphene+oxide+tubes+using+green+chemistry+and+their+potential+use+as+reinforcement+materials+for+biomedical+applications.">Synthesis of irregular graphene oxide tubes using green chemistry and their potential use as reinforcement materials for biomedical applications.</a> PLoS One. 12 (9), e0185235 (2017).</li><li>S&#225;nchez-Correa, F., Vidaurre-Agut, C., Serrano-Aroca, A., Campillo-Fern&#225;ndez, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(2-hydroxyethyl+acrylate)+hydrogels+reinforced+with+graphene+oxide:+Remarkable+improvement+of+water+diffusion+and+mechanical+properties.">Poly(2-hydroxyethyl acrylate) hydrogels reinforced with graphene oxide: Remarkable improvement of water diffusion and mechanical properties.</a> J Appl Polym Sci. , (2018).</li><li>Serrano-Aroc, &. #. 1. 9. 3. ;., Iskandar, L., Deb, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Green+synthetic+routes+to+alginate-graphene+oxide+composite+hydrogels+with+enhanced+physical+properties+for+bioengineering+applications.">Green synthetic routes to alginate-graphene oxide composite hydrogels with enhanced physical properties for bioengineering applications.</a> Eur Polym J. 103, 198-206 (2018).</li><li>Llorens-G&#225;mez, M., Serrano-Aroca, &. #. 1. 9. 3. ;. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-Cost+Advanced+Hydrogels+of+Calcium+Alginate/Carbon+Nanofibers+with+Enhanced+Water+Diffusion+and+Compression+Properties.">Low-Cost Advanced Hydrogels of Calcium Alginate/Carbon Nanofibers with Enhanced Water Diffusion and Compression Properties.</a> Polymers (Basel). 10 (4), 405 (2018).</li><li>Bauer, A. W., Kirby, W. M. M., Sherris, J. C., Turck, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibiotic+susceptibility+testing+by+a+standardized+single+disk+method.">Antibiotic susceptibility testing by a standardized single disk method.</a> A J Clin Pathol. 45, 493-496 (1966).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ISO Specification 22196: measurement of antibacterial activity on plastics surfaces. , 584 (2007).</li><li>Taubes, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+bacteria+fight+back.">The bacteria fight back.</a> Science. 321 (5887), 356-361 (2008).</li><li>Boucher, H. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=10+x+'20+progress--development+of+new+drugs+active+against+Gram-negative+bacilli:+an+update+from+the+infectious+diseases+society+of+America.">10 x '20 progress--development of new drugs active against Gram-negative bacilli: an update from the infectious diseases society of America.</a> Clinical Infectious Diseases. 56 (12), 1685-1694 (2013).</li></ol>

The authors have nothing to disclose.

The antimicrobial activity of new advanced materials can be analyzed by this easy-to-follow protocol consisting of 2 complementary procedures based on 2 existing methods: the agar disk diffusion test38&#160;and the antimicrobial activity measured on material surfaces according to the ISO 22196:2007 norm39.
In this research field, many of the antimicrobial tests reported in the literature are highly assay-dependent. Therefore, it is very important to have detailed and consistent protocols in place across laboratories. This article is a step in that direction. Furthermore, it could be very helpful for many researchers who are less experienced in this field and require in-depth, step-by-step procedures to follow for accurate results.
This protocol can be used with many types of materials cut into disk shapes of 10-mm diameter. Brittle materials can be swollen in a suitable solvent for 1 h to render the cutting process easier. Thus, hydrophilic materials such as alginates can be hydrated in autoclaved distilled water. Other solvents, such as ethanol, ketone, and dichloromethane, can be employed to swell hydrophobic materials for 1 h before cutting them. However, some materials such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) do not need to be swollen and they can be cut directly. After that, it is very important to dry the sample material disks in a vacuum oven and sterilize each specimen with ethanol and UV radiation for 1 h to avoid any contamination risk.
This protocol recommends TSA and TSB as culture media and the use of pure cultures of 3 microorganisms to reach a broad range of microorganisms: the Gram-positive bacteria Staphylococcus aureus, the Gram-negative bacteria Escherichia coli, and the yeast Candida albicans. However, alternative culture media and other microorganisms in need of different incubation conditions could also be used with this protocol. Sometimes, only 1 microorganism is tested to have an initial idea of the antimicrobial activity of a new material.
The materials showing strong antimicrobial activity against the recommended 3 different types of microorganisms should also be tested against antibiotic-resistant pathogens such as methicillin-resistant Staphylococcus epidermidis (MRSE), which have been successfully utilized with this protocol. Other important drug-resistant microorganisms which are causing much concern are the Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE), and the Gram-negative Pseudomonas aeruginosa40,41.
Biofilm inhibition and the antimicrobial activity of materials against other types of microorganisms such as viruses and parasites cannot be tested with this protocol. However, this protocol provides a very useful starting point for an antimicrobial study of a new advanced material.
In the antimicrobial agar disk diffusion test, a critical step occurs when the sample disk has to be placed in the center of the plate because some materials fold as soon as they get in contact with the agar media. In this case, it is recommended to use a sterile pair of tweezers to carefully unfold the sample. On the other hand, in the contact method, it is critical to wash the control and sample disks very well with PBS by pipetting them four times followed by a vigorous vortexing and sonication in order to ensure that no viable microorganisms remain adhered to the material surface.
This video protocol can be utilized in many bioengineering applications, such as bioprocess engineering, tissue engineering, controlled drug delivery, packaging materials, wastewater treatment, and agriculture, which use biomaterials with a highly desirable antimicrobial capacity.
The results obtained with this protocol are qualitative (the images) and quantitative (the normalized width of the antibacterial &#34;halo&#34; and the loss of viability) with a good analysis of its reproducibility (mean &#177; standard deviation). When comparing different materials, these mean values obtained with the diffusion and contact method results analysis must be analyzed by one-way ANOVA, followed by Turkey&#39;s post hoc analysis, in order to study if they are, statistically, significantly different (p &#60;0.01).

Implant failure is often a consequence of microbial infections that occur in spite of antimicrobial prophylaxis and aseptic working conditions. This problem is causing very high healthcare costs and is distressing among patients1. Important bacteria such as Staphylococcus aureus are currently considered to be very dangerous pathogens in nosocomial infections associated with catheters and other medical implants and are the main contaminants of medical instruments2. Therefore, the development of novel antimicrobial strategies is urgently needed for both daily and medical uses.
Antimicrobial agents include antibiotics3, quaternary ammonium compounds4, metal ions/oxides5, and antimicrobial peptides (AMPs)6. Antibiotics are gradually becoming less efficient due to bacterial resistance7, which is on the rise due to antibiotic overuse8. Quaternary ammonium compounds are only very efficient for a short-term use because of microbial resistance9. Metal ions/oxides have long been utilized as very effective antimicrobial agents and are used in many common commercial products including bandages, water filters, paints, etc.10,11,12. However, it has been demonstrated that these types of compounds can be toxic to some types of mammalian cells13.
AMPs show excellent antimicrobial and immunomodulatory properties14,15, and bacteria seem to find it very difficult to develop a resistance against them16. However, the process to produce pure AMPs is expensive; therefore, a large-scale production is not viable. Thus, strategies to counter the problems in producing AMPs have been developed (e.g., small molecular antibacterial peptoid mimics17, peptoids18, &#945;-peptides19 and &#946;-peptides20). Methacrylate-ended polypeptides and polypeptoids have been synthesized for antimicrobial and antifouling coatings21.
The development of new antimicrobial agents such as advanced materials in pure or hybrid form, able to prevent and treat multidrug-resistant infections, is increasingly necessary. A broad range of new advanced materials for many bioengineering fields such as tissue and bioprocess engineering have been developed with improved chemical and physical properties in the last decades through several methods: plasma-polymerization grafting onto a hydrophobic substrate22,23,24, tailoring of crosslinking density25,26, polymerization in solution27,28,29,30, porogen dissolution31,32, and by the incorporation of nanomaterials such as graphene oxide (GO)33,34,35,36&#160;and carbon nanofibers (CNFs)37.
The study of the antimicrobial capacity of these new materials could exponentially increase their potential bioengineering applicability and has, therefore, become essential. We present an easy-to-follow protocol to quantify the antimicrobial activity of such new advanced materials. Here, after the sample preparation, two complementary methods are followed: the first is based on the agar disk diffusion test38&#160;(diffusion method) and the second is based on the ISO 22196:2007 norm39&#160;to measure the antimicrobial activity on material surfaces (contact method).

<table><tbody><tr><td>Cylindrical punch&amp;nbsp;</td><td></td><td></td><td>10 mm diameter</td></tr><tr><td>Petri dishes</td><td>soria genlab</td><td>P101</td><td>90 mm diameter, sterile</td></tr><tr><td>Tryptic soy agar (TSA)</td><td>Liofilchem</td><td>610052</td><td>Dehydrated medium 500 g (powder)</td></tr><tr><td>Tryptic soy broth (TSB)</td><td>Liofilchem</td><td>610053</td><td>Dehydrated medium 500 g (powder)</td></tr><tr><td>Sterile cotton swab</td><td>EUTOTUBO</td><td>300200</td><td></td></tr><tr><td>Centrifuge tubes</td><td>VIDRA FOC, SA</td><td>429900</td><td>50 mL, sterile</td></tr><tr><td>Ethanol</td><td>VWR</td><td>83813360</td><td>Absolute ethanol</td></tr><tr><td>Sterile 48-wells plate</td><td>COSTAR</td><td>3548</td><td>Flat bottom with lid, tissue culture treated, non-pyrogenic, polystyrene</td></tr><tr><td>A pair of tweezers</td><td>BRAUN</td><td>24612036</td><td>Toothless</td></tr><tr><td>Sterile phosphate buffered saline (PBS).</td><td>VWR</td><td>E404-100TAPBS</td><td></td></tr><tr><td>Vaccum oven with a connected vacuum pump</td><td>JP Selecta, SA</td><td>5900620</td><td></td></tr><tr><td>Laminar flow hood</td><td>TELSTAR Technologies, SL</td><td>TELSTAR AH-100</td><td>12.0 W lamp of UV-C radiation</td></tr><tr><td>Class II Biological safety cabinet</td><td>LABOGENE</td><td>MARS 1200</td><td></td></tr><tr><td>Incubator</td><td>ASTEC CO, LTD</td><td>SCA-165DR</td><td></td></tr><tr><td>Vortex mixer</td><td>Biosan</td><td>V-1 Plus</td><td></td></tr><tr><td>Spectrophotometer</td><td>Macherey-Nagel, Germany</td><td>Nanocolor UV/VIS II</td><td></td></tr><tr><td>Bunsen burner</td><td>JP Selecta, SA</td><td>7001539</td><td></td></tr><tr><td>Alcohol burner</td><td>VIDRA FOC, SA</td><td>1658/20</td><td>In case sterilisation is necessary to be performed inside class II biological safety cabinet</td></tr><tr><td>Orbital shaker</td><td>sartorius stedim</td><td>8864845</td><td></td></tr><tr><td>Sonicator</td><td>SELECTA</td><td>3000617</td><td>50/60 Hz</td></tr><tr><td>Digital calliper</td><td>ACHA</td><td>17-260</td><td>0-150 mm</td></tr><tr><td>Serological pipette</td><td>Fisherbrand</td><td>13-678-11</td><td>25 mL, sterile</td></tr><tr><td>Serological pipette</td><td>VWR</td><td>612-4950</td><td>5 mL, sterile</td></tr><tr><td>Serological pipette</td><td>VWR</td><td>612-5541</td><td>10 mL, sterile</td></tr><tr><td>Micropipette</td><td>GILSON</td><td>FA10005P</td><td>Pipetman L P200L, plastic 20-200 &amp;micro;L</td></tr><tr><td>Micropipette</td><td>GILSON</td><td>F123602</td><td>Pipetman P1000, 200-1000 &amp;micro;L</td></tr><tr><td>Micropipette&amp;nbsp;</td><td>GILSON</td><td>FA10016</td><td>Pipetman L P12X300L, 20-300 &amp;micro;L</td></tr><tr><td>Micropipette tips</td><td>LABBOX</td><td>TIBP-200-960</td><td>2-200 &amp;micro;L</td></tr><tr><td>Micropipette tips</td><td>LABBOX</td><td>TIBP-1K0-480</td><td>100-1000 &amp;micro;L</td></tr><tr><td>Pre-sterilized tube&amp;nbsp;</td><td>INSULAB</td><td>301402</td><td>10 mL&amp;nbsp;</td></tr><tr><td>Photo camera</td><td>Canon EOS 5D</td><td></td><td>Any camera with high resolution can also be utilized</td></tr><tr><td>&lt;em&gt;Gram-positive bacteria Staphylococcus aureus&lt;/em&gt;</td><td></td><td>&amp;nbsp;strain V329</td><td>Cucarella et al. &lt;em&gt;J Bacteriol&lt;/em&gt; &lt;strong&gt;183 (9)&lt;/strong&gt;,&amp;nbsp; 2888&amp;ndash;2896 (2001)</td></tr><tr><td>Gram-negative bacteria &lt;em&gt;Escherichia coli&lt;/em&gt;</td><td>Colecci&amp;oacute;n Espa&amp;ntilde;ola de Cultivos Tipo CECT</td><td>CECT 101</td><td></td></tr><tr><td>Yeast &lt;em&gt;Candida albicans&lt;/em&gt;</td><td>Colecci&amp;oacute;n Espa&amp;ntilde;ola de Cultivos Tipo CECT</td><td>CECT 1394</td><td></td></tr><tr><td>Microcentrifuge tubes&amp;nbsp;</td><td>DASLAB</td><td>175508</td><td>1,5 mL</td></tr><tr><td>Autoclave</td><td>JP Selecta, SA</td><td>4002136</td><td></td></tr><tr><td>Spectrophotometer-cuvettes</td><td>UVAT Bio CB</td><td>F-0902-02</td><td>4,5 mL</td></tr><tr><td>Drigalski spatula</td><td>LABBOX</td><td>SPRP-L05-1K0</td><td>Sterile, disposable&amp;nbsp;</td></tr><tr><td>glass balls (2 mm diameter)</td><td>Hecht Karl</td><td>1401/2</td><td>Autoclavable, alternative device to the Drigalski spatula</td></tr><tr><td>Autoclave bags</td><td>DELTALAB</td><td>200318</td><td>To sterilize microbiological residues or contaminated material</td></tr><tr><td>Electronic pipette filling device</td><td>JetPip</td><td>JET BIOFIL</td><td></td></tr><tr><td>Laboratory bottle with ISO thread, graduated, borosilicate 3.3</td><td>LABBOX</td><td>SBG3-100-010</td><td>100 mL, for autoclaving culture media</td></tr><tr><td>Laboratory bottle with ISO thread, graduated, borosilicate 3.3</td><td>LABBOX</td><td>SBG3-250-010</td><td>250 mL, for autoclaving culture media</td></tr><tr><td>Laboratory bottle with ISO thread, graduated, borosilicate 3.3</td><td>LABBOX</td><td>SBG3-500-010</td><td>500 mL, for autoclaving culture media</td></tr><tr><td>Laboratory bottle with ISO thread, graduated, borosilicate 3.3</td><td>LABBOX</td><td>SBG3-1K0-010</td><td>1000 mL, for autoclaving culture media</td></tr><tr><td>Latex gloves</td><td>DENIA</td><td>2278000000</td><td></td></tr><tr><td>Indicator tape for sterilization</td><td>LABBOX</td><td>STAP-A55-001</td><td>Self-adhesive tape with impregnated paper turning to colour when exposed to sterilization process.</td></tr><tr><td>Universal test tube rack</td><td>LABBOX</td><td>MTSP-001-001</td><td>To hold centrifuge tubes</td></tr><tr><td>Microcentrifuge tube rack</td><td>VWR</td><td>211-0210</td><td>To hold microcentrifuge tubes</td></tr><tr><td>Sterile loop</td><td>ACEFE S.A.</td><td>100140055</td><td>10 &amp;micro;L of capacity for microbial culture&amp;nbsp;</td></tr><tr><td>Material M1</td><td>Universidad Cat&amp;oacute;lica de Valencia San Vicente M&amp;aacute;rtir (UCV)</td><td></td><td>Material type 1&amp;nbsp;</td></tr><tr><td>Material M2</td><td>Universidad Cat&amp;oacute;lica de Valencia San Vicente M&amp;aacute;rtir (UCV)</td><td></td><td>Material type 2&amp;nbsp;</td></tr><tr><td>Material M3</td><td>Universidad Cat&amp;oacute;lica de Valencia San Vicente M&amp;aacute;rtir (UCV)</td><td></td><td>Material type3</td></tr><tr><td>Material M4</td><td>Universidad Cat&amp;oacute;lica de Valencia San Vicente M&amp;aacute;rtir (UCV)</td><td></td><td>Material type 4&amp;nbsp;</td></tr><tr><td>Material C</td><td>Universidad Cat&amp;oacute;lica de Valencia San Vicente M&amp;aacute;rtir (UCV)</td><td></td><td>Control material</td></tr></tbody></table>

antimicrobial characterization of advanced materials for bioengineering applications

The development of new advanced materials with enhanced properties is becoming more and more important in a wide range of bioengineering applications. Thus, many novel biomaterials are being designed to mimic specific environments required for biomedical applications such as tissue engineering and controlled drug delivery. The development of materials with improved properties for the immobilization of cells or enzymes is also a current research topic in bioprocess engineering. However, one of the most desirable properties of a material in these applications is the antimicrobial capacity to avoid any undesirable infections. For this, we present easy-to-follow protocols for the antimicrobial characterization of materials based on (i) the agar disk diffusion test (diffusion method) and (ii) the ISO 22196:2007 norm to measure the antimicrobial activity on material surfaces (contact method). This protocol must be performed using Gram-positive and Gram-negative bacteria and yeast to cover a broad range of microorganisms. As an example, 4 materials with different chemical natures are tested following this protocol against Staphylococcus aureus, Escherichia coli, and Candida albicans.The results of these tests exhibit non-antimicrobial activity for the first material and increasing antibacterial activity against Gram-positive and Gram-negative bacteria for the other 3 materials. However, none of the 4 materials are able to inhibit the growth of Candida albicans.

This protocol was employed, as an example, to test the antimicrobial capacity of 4 materials with different chemical natures against the 3 recommended microorganisms: Staphylococcus aureus, Escherichia coli, and Candida albicans.The results of the agar disk diffusion tests (diffusion method) exhibited non-antimicrobial activity for the first material (M1) as it occured in the control disk (C, image not shown) and increasing antibacterial activity against Gram-positive and Gram-negative bacteria for the other 3 materials M2, M3 and M4&#160;(see Figure 2).
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57710/57710fig2.jpg" /> 
Figure 2: Antimicrobial diffusion method results. This panel shows the antimicrobial diffusion method for the 4 material (M1, M2, M3, and M4) disks (10 mm diameter x 1 mm thickness) against S. aureus and E. coli after 24 h of incubation. <a href="/files/ftp_upload/57710/57710fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 3 shows the different normalized widths of the antimicrobial &#34;halo&#34; (nwhalo) for the different example materials M1, M2, M3, and M4 against Gram-positive and Gram-negative bacteria calculated with equation (1). However, none of the 4 materials were able to inhibit the growth of the yeast Candida albicans (images not shown).
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57710/57710fig3v2.jpg" /> 
Figure 3: Antimicrobial diffusion &#34;halo&#34; results. This panel shows the normalized &#34;halo&#34; (nwhalo) for each material (M1, M2, M3, and M4) disk (10 mm diameter x 1 mm thickness) against S. aureus and E. coli after 24 h of incubation. The differences are statistically significant (p &#60;0.01). However, sample M1 exhibited no antimicrobial activity. <a href="/files/ftp_upload/57710/57710fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The results of the contact method also exhibited non-antimicrobial activity for the first material (M1) as it occurred in the control disk (C) and increasing antibacterial activity against Grampositive and Gram-negative bacteria for the other 3 materials (see Figure 4).
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57710/57710fig4v3.jpg" /> 
Figure 4: Antimicrobial contact method results. This panel shows the respective 90 mm plates of the 4 material (M1, M2, M3, and M4) surface antimicrobial activity assay according to the ISO 22196:2007 after 24 h of incubation for S. aureus and E. coli (dilution factor of 10-4). C&#160;is the viable bacteria recovered from the control disk after 24 h of incubation. <a href="/files/ftp_upload/57710/57710fig4v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The loss of viability (%) was determined by equation (2) and (3) as indicated in this protocol (see Figure 5).
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57710/57710fig5v2.jpg" /> 
Figure 5: Loss of viability by contact method. This panel shows the loss of viability (%) for M1, M2, M3, and M4 against S. aureus and E. coli on the material surfaces. Sample M1 exhibited no antimicrobial activity. <a href="/files/ftp_upload/57710/57710fig5v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
However, none of the 4 materials were able to inhibit the growth of the yeast Candida albicans by the contact method either (images not shown). Therefore, 3 of these 4 advanced materials showed positive antimicrobial results against Gram-positive and Gram-negative bacteria and thus could be very useful for many bioengineering applications with high antibacterial activity requirements. However, none of the 4 materials were able to inhibit the yeast growth.

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Antimicrobial Characterization of Advanced Materials for Bioengineering Applications

We present a protocol for the antimicrobial characterization of advanced materials. Here, the antimicrobial activity on material surfaces is measured by two methods that complement each other: one is based on the agar disk diffusion test, and the other is a standard procedure based on the ISO 22196:2007 norm.

The development of new advanced materials with enhanced properties is becoming more and more important in a wide range of bioengineering applications. ...

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Research

JoVE Journal

Bioengineering

21.9K Views.  Universidad Católica de Valencia San Vicente Mártir. We present a protocol for the antimicrobial characterization of advanced materials. Here, the antimicrobial activity on material surfaces is measured by two methods that complement each other: one is based on the agar disk diffusion test, and the other is a standard procedure based on the ISO 22196:2007 norm.

Video: Antimicrobial Characterization of Advanced Materials for Bioengineering Applications

High-throughput Identification of Bacteria Repellent Polymers for Medical Devices

Medical devices are often associated with hospital-acquired infections, which place enormous strain on patients and the healthcare system as well as contributing to antimicrobial resistance. One possible avenue for the reduction of device-associated infections is the identification of bacteria-repellent polymer coatings for these devices, which would prevent bacterial binding at the initial attachment step. A method for the identification of such repellent polymers, based on the parallel screening of hundreds of polymers using a microarray, is described here. This high-throughput method resulted in the identification of a range of promising polymers that resisted binding of various clinically relevant bacterial species individually and also as multi-species communities. One polymer, PA13 (poly(methylmethacrylate-co-dimethylacrylamide)), demonstrated significant reduction in attachment of a number of hospital isolates when coated onto two commercially available central venous catheters. The method described could be applied to identify polymers for a wide range of applications in which modification of bacterial attachment is important.

A high-throughput microarray method for the identification of polymers which reduce bacterial surface binding on medical devices is described.

Medical devices are often associated with hospital-acquired infections, which place enormous strain on patients and the healthcare system as well as ...

Biomimetic Materials to Characterize Bacteria-host Interactions

Bacterial attachment to host cells is one of the earliest events during bacterial colonization of host tissues and thus a key step during infection. The biochemical and functional characterization of adhesins mediating these initial bacteria-host interactions is often compromised by the presence of other bacterial factors, such as cell wall components or secreted molecules, which interfere with the analysis. This protocol describes the production and use of biomimetic materials, consisting of pure recombinant adhesins chemically coupled to commercially available, functionalized polystyrene beads, which have been used successfully to dissect the biochemical and functional interactions between individual bacterial adhesins and host cell receptors. Protocols for different coupling chemistries, allowing directional immobilization of recombinant adhesins on polymer scaffolds, and for assessment of the coupling efficiency of the resulting &#8220;bacteriomimetic&#8221; materials are also discussed. We further describe how these materials can be used as a tool to inhibit pathogen mediated cytotoxicity and discuss scope, limitations and further applications of this approach in studying bacterial - host interactions.

Bacterial attachment to host cells is a key step during host colonization and infection. This protocol describes the generation of polymer-coupled recombinant adhesins as biomimetic materials which allow analysis of the contribution of individual adhesins to these processes, independent of other bacterial factors.

Bacterial attachment to host cells is one of the earliest events during bacterial colonization of host tissues and thus a key step during infection. The ...

Immunology and Infection

Qualitative and Quantitative Assays for Detection and Characterization of Protein Antimicrobials

Initial evaluations of large microbial libraries for potential producers of novel antimicrobial proteins require both qualitative and quantitative methods to screen for target enzymes prior to investing greater research effort and resources. The goal of this protocol is to demonstrate two complementary assays for conducting these initial evaluations. The microslide diffusion assay provides an initial or simple detection screen to enable the qualitative and rapid assessment of proteolytic activity against an array of both viable and heat-killed bacterial target substrates. As a counterpart, the increased sensitivity and reproducibility of the dye-release assay provides a quantitative platform for evaluating and comparing environmental influences affecting the hydrolytic activity of protein antimicrobials. The ability to label specific heat-killed cell culture substrates with Remazol brilliant blue R dye expands this capability to tailor the dye-release assay to characterize enzymatic activity of interest.

Here, we present protocols to rapidly screen and characterize enzymes for antimicrobial activity. The microslide diffusion assay and the dye-release assay utilize target bacterial substrates for qualitative and quantitative enzymatic activity evaluation.

Initial evaluations of large microbial libraries for potential producers of novel antimicrobial proteins require both qualitative and quantitative methods ...

Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay

Most pathogenic bacteria are able to form biofilms during infection, but due to the difficulty of manipulating and assessing biofilms, the vast majority of laboratory work is conducted with planktonic cells. Here, we describe a peg plate biofilm assay as performed with Staphylococcus aureus. Bacterial biofilms are grown on pegs attached to a 96-well microtiter plate lid, washed through gentle submersion in buffer, and placed in a drug challenge plate. After subsequent incubation they are again washed and moved to a final recovery plate, in which the fluorescent dye resazurin serves as a viability indicator. This assay offers greatly increased ease-of-use, reliability, and reproducibility, as well as a wealth of data when conducted as a kinetic read. Moreover, this assay can be adapted to a medium-throughput drug screening approach by which an endpoint fluorescent readout is taken instead, offering a path for drug discovery efforts.

Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay

Most bacterial infections produce a biofilm. By virtue of their environment, biofilm associated bacteria are often phenotypically drug resistant. Novel antibacterial molecules that kill bacteria in biofilms are thus a high priority. We establish an assay to quickly screen for antimicrobial compounds that are effective at eradicating biofilms.

Most pathogenic bacteria are able to form biofilms during infection, but due to the difficulty of manipulating and assessing biofilms, the vast majority ...

A Platform of Anti-biofilm Assays Suited to the Exploration of Natural Compound Libraries

Biofilms are regarded as one of the most challenging topics of modern biomedicine, and they are potentially responsible for over 80% of antibiotic-tolerant infections. Biofilms have displayed an exceptionally high tolerance for chemotherapy, which is thought to be multifactorial. For instance, the matrix provides a physical barrier that decreases the penetration of antibiotics into the biofilm. Also, cells within the biofilms are phenotypically diverse. Likely, biofilm resilience arises from a combination of these and other, yet unknown, mechanisms. All of the currently existing antibiotics have been developed against single-cells (planktonic) bacteria. Therefore, so far, a very limited repertoire of molecules exists that can selectively act on mature biofilms. This situation has driven a progressive paradigm shift in drug discovery, in which searching for anti-biofilms has been urged to occupy a more prominent place. An additional challenge is that there are a very limited number of standardized methods for biofilm research, especially those that can be used for large-throughput screening of chemical libraries. Here, an experimental anti-biofilm platform for chemical screening is presented. It uses three assays to measure biofilm viability (with resazurin staining), total biomass (with crystal violet staining), and biofilm matrix (using a wheat germ agglutinin, WGA-fluorescence-based staining of the poly-N-acetyl-glucosamine, PNAG, fraction). All the assays were developed using Staphylococcus aureus as the model bacteria. Examples of how the platform can be used for primary screening as well as for functional characterization of identified anti-biofilm hits are presented. This experimental sequence further allows for the classification of the hits based upon the measured end-points. It also provides information on their mode of action, especially on long-term versus short-term chemotherapeutic effects. Thus, it is very advantageous for the quick identification of high-quality hit compounds that can serve as starting points for various biomedical applications.

Biofilm infections show high tolerance towards chemotherapy. No single assay captures the complexity of biofilms. Instead, complementary assays are needed. We present a screening platform (developed for S. aureus) that combines assays for viability, biomass, and biofilm matrix. It allows anti-biofilm drug discovery, including the assessment of long-term chemotherapeutic effects.

Biofilms are regarded as one of the most challenging topics of modern biomedicine, and they are potentially responsible for over 80% of ...

Synthesis of Multi-walled Carbon Nanotubes Modified with Silver Nanoparticles and Evaluation of Their Antibacterial Activities and Cytotoxic Properties

In this study, multi-walled carbon nanotubes (MWCNTs) were treated with an aqueous sulfuric acid solution to form an oxygen-based functional group. Silver MWCNTs were prepared by the reductive deposition of silver from an aqueous solution of AgNO3 on the oxidized MWCNTs. Given the unique color of the CNTs, it was not possible to apply them to the minimum inhibitory concentration or mitochondrial toxicity assays to evaluate the toxicity and antibacterial properties, since they would interfere with the assays. The inhibition zone and minimum bactericidal concentration for the Ag-MWCNTs were measured and Live/Dead and Trypan Blue assays were used to measure the toxicity and antibacterial properties without interfering with the color of the CNTs.

In this study, antimicrobial nanomaterials were synthesized by acidic oxidation of multiwalled carbon nanotubes and subsequent reductive deposition of silver nanoparticles. Antimicrobial activity and cytotoxicity tests were performed with the as-prepared nanomaterials.

In this study, multi-walled carbon nanotubes (MWCNTs) were treated with an aqueous sulfuric acid solution to form an oxygen-based functional group. Silver ...

Evaluation of Antimicrobial Activities of Nanoparticles and Nanostructured Surfaces In Vitro

The antimicrobial activities of nanoparticles and nanostructured surfaces, such as silver, zinc oxide, titanium dioxide, and magnesium oxide, have been explored previously in clinical and environmental settings and in consumable food products. However, a lack of consistency in the experimental methods and materials used has culminated in conflicting results, even amongst studies of the same nanostructure types and bacterial species. For researchers who wish to employ nanostructures as an additive or coating in a product design, these conflicting data limit their utilization in clinical settings. 
To confront this dilemma, in this article, we present four different methods to determine the antimicrobial activities of nanoparticles and nanostructured surfaces, and discuss their applicability in different scenarios. Adapting consistent methods is expected to lead to reproducible data that can be compared across studies and implemented for different nanostructure types and microbial species. We introduce two methods to determine the antimicrobial activities of nanoparticles and two methods for the antimicrobial activities of nanostructured surfaces. 
For nanoparticles, the direct co-culture method can be used to determine the minimum inhibitory and minimum bactericidal concentrations of nanoparticles, and the direct exposure culture method can be used to assess real-time bacteriostatic versus bactericidal activity resulting from nanoparticle exposure. For nanostructured surfaces, the direct culture method is used to determine the viability of bacteria indirectly and directly in contact with nanostructured surfaces, and the focused-contact exposure method is used to examine antimicrobial activity on a specific area of a nanostructured surface. We discuss key experimental variables to consider for in vitro study design when determining the antimicrobial properties of nanoparticles and nanostructured surfaces. All these methods are relatively low cost, employ techniques that are relatively easy to master and repeatable for consistency, and are applicable to a broad range of nanostructure types and microbial species.

Evaluation of Antimicrobial Activities of Nanoparticles and Nanostructured Surfaces In Vitro

We introduce four methods to evaluate the antimicrobial activities of nanoparticles and nanostructured surfaces using in vitro techniques. These methods can be adapted to study the interactions of different nanoparticles and nanostructured surfaces with a broad range of microbial species.

The antimicrobial activities of nanoparticles and nanostructured surfaces, such as silver, zinc oxide, titanium dioxide, and magnesium oxide, have been ...

Generation of Greater Bacterial Biofilm Biomass using PCR-Plate Deep Well Microplate Devices

Bacterial biofilms are difficult to eradicate from surfaces using conventional antimicrobial interventions. High-throughput 96-well microplate methods are frequently used to cultivate bacterial biofilms for rapid antimicrobial susceptibility testing to calculate minimal biofilm eradication concentration (MBEC) values. Standard biofilm devices consist of polystyrene pegged-lids fitted to 96-well microplates and are ideal for measuring biofilm biomass and MBEC values, but these devices are limited by available peg surface area for biomass accumulation and cost. Here, we outline a protocol to use self-assembled polypropylene 96-well deep well PCR-plate pegged-lid device to grow Escherichia coli BW25113 and Pseudomonas aeruginosa PAO1 biofilms. A comparison of 24-hour biofilms formed on standard and deep well devices by each species using crystal violet biomass staining and MBEC determination assays are described. The larger surface area of deep well devices expectedly increased overall biofilm formation by both species 2-4-fold. P. aeruginosa formed significantly greater biomass/mm2 on deep well pegs as compared to the standard device. E. coli had greater biomass/mm2 on standard polystyrene devices as compared the deep well device. Biofilm eradication assays with disinfectants such as sodium hypochlorite (bleach) or benzalkonium chloride (BZK) showed that both compounds could eliminate E. coli and P. aeruginosa biofilms from both devices but at different MBEC values. BZK biofilm eradication resulted in variable E. coli MBEC values between devices, however, bleach demonstrated reproducible MBEC values for both species and devices. This study provides a high throughput deep well method for growing larger quantities of biofilms on polypropylene devices for downstream studies requiring higher amounts of static biofilm.

This protocol presents methodology to perform biofilm growth and biomass measurements using self-assembled deep well PCR-plate devices for high-throughput 96-well pegged lid static biofilm screening.

Bacterial biofilms are difficult to eradicate from surfaces using conventional antimicrobial interventions. High-throughput 96-well microplate methods are ...

 Zinc Oxide Nanoparticles Synthesis and Analysis of its Antibacterial Effects

Preparation of Zinc Oxide Nanoparticles and the Evaluation of their Antibacterial Effects

Nosocomial bacterial infections have become increasingly challenging due to their inherent resistance to antibiotics. The emergence of multidrug-resistant bacterial strains in hospitals has been attributed to the extensive and varied use of antibiotics, further exacerbating the problem of antibiotic resistance. Metal nanomaterials have been widely studied as an alternative solution for eradicating antibiotic-resistant bacterial cells. Metallic nanoparticles attack bacterial cells through various mechanisms, such as the release of antibacterial ions, generation of reactive oxygen species, or physical disruption, against which bacteria cannot develop resistance. Among the actively researched antimicrobial metal nanoparticles, zinc oxide nanoparticles, which are FDA-approved, are known for their biocompatibility and antibacterial properties. In this study, we focused on successfully developing a precipitation method for synthesizing zinc oxide nanoparticles, analyzing the properties of these nanoparticles, and conducting antimicrobial tests. Zinc oxide nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), ultraviolet/visible spectroscopy, and X-ray diffraction (XRD). Antibacterial tests were conducted using the broth microdilution test with the multidrug-resistant strains of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. This study demonstrated the potential of zinc oxide nanoparticles in inhibiting the proliferation of antibiotic-resistant bacteria.

Author Spotlight: Exploring the Antibacterial Effects of Zinc Oxide Nanoparticles in Overcoming Antibiotic Resistance

In this study, zinc oxide nanoparticles were synthesized using a precipitation method. The antibacterial effect of the synthesized particles was tested against multidrug-resistant methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa bacterial strains.

Nosocomial bacterial infections have become increasingly challenging due to their inherent resistance to antibiotics. The emergence of multidrug-resistant ...

Antibacterial Graphene Oxide/Copper Nanocomposites for Resistant Bacteria

Fabrication of Antibacterial Graphene Oxide/Copper Nanocomposites

Antibiotics are currently the most used antibacterial treatment for killing bacteria. However, bacteria develop resistance when continually overexposed to antibiotics. Developing&#160;antimicrobial agents that can replace existing antibiotics is essential because antibiotic-resistant bacteria have resistance mechanisms for all current antibiotics and can promote nosocomial infections. To address this challenge, in this study, we propose graphene oxide/copper (GO/Cu) nanocomposites as antibacterial materials that can replace the existing antibiotics. GO/Cu nanocomposites are characterized by transmission electron microscopy and scanning electron microscopy. They show that copper (Cu) nanoparticles are well-grown on the graphene oxide sheets. Additionally, a microdilution broth method is used to confirm the efficacy of the antimicrobial substance against methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (P. aeruginosa), which are frequently implicated in nosocomial infections. Specifically, 99.8% of MRSA and 84.7% of P. aeruginosa are eliminated by 500 &#181;g/mL of GO/Cu nanocomposites. Metal nanocomposites can eradicate antibiotic-resistant bacteria by releasing ions, forming reactive oxygen species, and physically damaging the bacteria. This study demonstrates the potential of antibacterial GO/Cu nanocomposites in eradicating antibiotic-resistant bacteria.

Author Spotlight: Metallic Nanocomposites to Eliminate Antibiotic-Resistant Bacteria

Herein, we introduce graphene oxide/copper (GO/Cu) nanocomposites as an antibacterial nanomaterial. The antibacterial effectiveness of the GO/Cu nanocomposites was evaluated against both antibiotic-resistant gram-positive and gram-negative bacteria.

Antibiotics are currently the most used antibacterial treatment for killing bacteria. However, bacteria develop resistance when continually overexposed to ...

Antimicrobial Characterization of Advanced Materials for Bioengineering Applications

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