Name: quantitative examination of antibiotic susceptibility of neisseria gonorrhoeae aggregates using atp-utilization commercial assays and live/dead staining
Uploaded: 2019-02-08T14:30:00
Description: Watch this Scientific Journal Video about Quantitative Examination of Antibiotic Susceptibility of Neisseria gonorrhoeae Aggregates Using ATP-utilization Commercial Assays and Live/Dead Staining at Jo

This work was supported by a grant from National Institute of Health to D.C.S. and W.S. AI123340. L.-C.W., J.W., A.C., and E.N. were supported in part/participate in &#34;The First-Year Innovation &#38; Research Experience&#34; program funded by the University of Maryland. The funders had no role in study design, data collection, and analysis, decision to publish, or preparation of the manuscript. We acknowledge the UMD CBMG Imaging Core for all microscopy experiments.

1. General maintenance of GC strains
<ol>
	<li>Streak N. gonorrhoeae strains on GCK agar with 1% Kellogg supplements18 (Table 1, Table 2) from freezer stocks and incubate 37 &#176;C with 5% CO2 for 16-18 h. Use MS11 expressing phase-variable Opa (MS11Opa+), no Opa (MS11&#916;Opa), or a truncated LOS (MS11&#916;LgtE).</li>
	<li>Carefully pick pili negative (colony without dark edge) or positive (colony with dark edge) colonies from each strain based on colony ...

<ol>
	<li>den Heijer, C. D., 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=A+comprehensive+overview+of+urogenital,+anorectal+and+oropharyngeal+Neisseria+gonorrhoeae+testing+and+diagnoses+among+different+STI+care+providers:+a+cross-sectional+study.">A comprehensive overview of urogenital, anorectal and oropharyngeal Neisseria gonorrhoeae testing and diagnoses among different STI care providers: a cross-sectional study.</a> BMC Infectious Diseases. 17 (1), (2017).</li><li>Hein, K., Marks, A., Cohen, M. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymptomatic+gonorrhea:+prevalence+in+a+population+of+urban+adolescents.">Asymptomatic gonorrhea: prevalence in a population of urban adolescents.</a> The Journal of Pediatrics. 90 (4), 634-635 (1977).</li><li>Hananta, I. P., 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=Gonorrhea+in+Indonesia:+High+Prevalence+of+Asymptomatic+Urogenital+Gonorrhea+but+No+Circulating+Extended+Spectrum+Cephalosporins-Resistant+Neisseria+gonorrhoeae+Strains+in+Jakarta,+Yogyakarta,+and+Denpasar,+Indonesia.">Gonorrhea in Indonesia: High Prevalence of Asymptomatic Urogenital Gonorrhea but No Circulating Extended Spectrum Cephalosporins-Resistant Neisseria gonorrhoeae Strains in Jakarta, Yogyakarta, and Denpasar, Indonesia.</a> Sexually Transmitted Diseases. 43 (10), 608-616 (2016).</li><li>Chlamydia, W. H. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chlamydia+trachomatis,+Neisseria+gonorrhoeae,+syphilis+and+Trichomonas+vaginalis.+Methods+and+results+used+by+WHO+to+generate+2005+estimates.+World+Health+Organisation,+2011.+Prevalence+and+incidence+of+selected+sexually+transmitted+infections.">Chlamydia trachomatis, Neisseria gonorrhoeae, syphilis and Trichomonas vaginalis. Methods and results used by WHO to generate 2005 estimates. World Health Organisation, 2011. Prevalence and incidence of selected sexually transmitted infections.</a> World Health Organisation. , (2011).</li><li>Mayor, M. T., Roett, M. A., Uduhiri, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diagnosis+and+management+of+gonococcal+infections.">Diagnosis and management of gonococcal infections.</a> American Family Physician. 86 (10), 931-938 (2012).</li><li>Alirol, E., 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=Multidrug-resistant+gonorrhea:+A+research+and+development+roadmap+to+discover+new+medicines.">Multidrug-resistant gonorrhea: A research and development roadmap to discover new medicines.</a> PLOS Medicine. 14 (7), (2017).</li><li>Workowski, K. A., Bolan, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sexually+transmitted+diseases+treatment+guidelines,+2015.">Sexually transmitted diseases treatment guidelines, 2015.</a> MMWR Recommendations and Reports. 64, 1-137 (2015).</li><li>Lahra, M. M., 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=Cooperative+Recognition+of+Internationally+Disseminated+Ceftriaxone-Resistant+Neisseria+gonorrhoeae+Strain.">Cooperative Recognition of Internationally Disseminated Ceftriaxone-Resistant Neisseria gonorrhoeae Strain.</a> Emerging Infectious Diseases. 24 (4), (2018).</li><li>Wi, T., 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=Antimicrobial+resistance+in+Neisseria+gonorrhoeae:+Global+surveillance+and+a+call+for+international+collaborative+action.">Antimicrobial resistance in Neisseria gonorrhoeae: Global surveillance and a call for international collaborative action.</a> PLOS Medicine. 14 (7), 1002344 (2017).</li><li>Singh, S., Singh, S. K., Chowdhury, I., Singh, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+Mechanism+of+Bacterial+Biofilms+Resistance+to+Antimicrobial+Agents.">Understanding the Mechanism of Bacterial Biofilms Resistance to Antimicrobial Agents.</a> Open Microbiology Journal. 11, 53-62 (2017).</li><li>Greiner, L. L., 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=Biofilm+Formation+by+Neisseria+gonorrhoeae.">Biofilm Formation by Neisseria gonorrhoeae.</a> Infection and Immunity. 73 (4), 1964-1970 (2005).</li><li>Zollner, R., Oldewurtel, E. R., Kouzel, N., Maier, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phase+and+antigenic+variation+govern+competition+dynamics+through+positioning+in+bacterial+colonies.">Phase and antigenic variation govern competition dynamics through positioning in bacterial colonies.</a> Scientific Reports. 7 (1), (2017).</li><li>Stein, D. C., 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=Expression+of+Opacity+Proteins+Interferes+with+the+Transmigration+of+Neisseria+gonorrhoeae.+across+Polarized+Epithelial+Cells.">Expression of Opacity Proteins Interferes with the Transmigration of Neisseria gonorrhoeae. across Polarized Epithelial Cells.</a> PLoS One. 10 (8), 0134342 (2015).</li><li>LeVan, A., 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=Construction+and+characterization+of+a+derivative+of+Neisseria+gonorrhoeae+strain+MS11+devoid+of+all+opa+genes.">Construction and characterization of a derivative of Neisseria gonorrhoeae strain MS11 devoid of all opa genes.</a> Journal of Bacteriology. 194 (23), 6468-6478 (2012).</li><li>Merritt, J. H., Kadouri, D. E., O'Toole, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growing+and+analyzing+static+biofilms.">Growing and analyzing static biofilms.</a> Curr Protoc Microbiol. , (2005).</li><li>Peeters, E., Nelis, H. J., Coenye, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+multiple+methods+for+quantification+of+microbial+biofilms+grown+in+microtiter+plates.">Comparison of multiple methods for quantification of microbial biofilms grown in microtiter plates.</a> Journal of Microbiological Methods. 72 (2), 157-165 (2008).</li><li>White, L. A., Kellogg, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neisseria+Gonorrhoeae+Identification+in+Direct+Smears+by+a+Fluorescent+Antibody-Counterstain+Method.">Neisseria Gonorrhoeae Identification in Direct Smears by a Fluorescent Antibody-Counterstain Method.</a> Journal of Applied Microbiology. 13, 171-174 (1965).</li><li>Swanson, J., Kraus, S. J., Gotschlich, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+on+gonococcus+infection.+I.+Pili+and+zones+of+adhesion:+their+relation+to+gonococcal+growth+patterns.">Studies on gonococcus infection. I. Pili and zones of adhesion: their relation to gonococcal growth patterns.</a> Journal of Experimental Medicine. 134 (4), 886-906 (1971).</li><li>Herten, M., 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=Rapid+in+Vitro+Quantification+of+S.+aureus+Biofilms+on+Vascular+Graft+Surfaces.">Rapid in Vitro Quantification of S. aureus Biofilms on Vascular Graft Surfaces.</a> Frontiers in Microbiology. 8, 2333 (2017).</li><li>Gracia, E., 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=In+vitro+development+of+Staphylococcus+aureus+biofilms+using+slime-producing+variants+and+ATP-bioluminescence+for+automated+bacterial+quantification.">In vitro development of Staphylococcus aureus biofilms using slime-producing variants and ATP-bioluminescence for automated bacterial quantification.</a> Luminescence. 14 (1), 23-31 (1999).</li><li>Webb, J. S., 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=Cell+death+in+Pseudomonas+aeruginosa+biofilm+development.">Cell death in Pseudomonas aeruginosa biofilm development.</a> Journal of Bacteriology. 185 (15), 4585-4592 (2003).</li><li>Jurcisek, J. A., Dickson, A. C., Bruggeman, M. E., Bakaletz, L. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+biofilm+formation+in+an+8-well+chamber+slide.">In vitro biofilm formation in an 8-well chamber slide.</a> Journal of visualized experiments. (47), (2011).</li><li>Wang, L. C., Litwin, M., Sahiholnasab, Z., Song, W., Stein, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neisseria+gonorrhoeae+Aggregation+Reduces+Its+Ceftriaxone+Susceptibility.">Neisseria gonorrhoeae Aggregation Reduces Its Ceftriaxone Susceptibility.</a> Antibiotics (Basel). 7 (2), (2018).</li><li>Lebeaux, D., Ghigo, J. M., Beloin, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biofilm-related+infections:+bridging+the+gap+between+clinical+management+and+fundamental+aspects+of+recalcitrance+toward+antibiotics.">Biofilm-related infections: bridging the gap between clinical management and fundamental aspects of recalcitrance toward antibiotics.</a> Microbiology and Molecular Biology Reviews. 78 (3), 510-543 (2014).</li><li>Hall-Stoodley, L., 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=Towards+diagnostic+guidelines+for+biofilm-associated+infections.">Towards diagnostic guidelines for biofilm-associated infections.</a> FEMS Immunology and Medical Microbiology. 65 (2), 127-145 (2012).</li></ol>

Bacteria can form biofilms during infection of the human body. Traditional MIC testing may not reflect the concentration needed to eradicate bacteria in a biofilm. To test antimicrobials effects on a biofilm, methods based on biofilm biomass as well as plating CFUs can be erroneous due to the impact of biofilm structure. For example, the plating method only works if the biofilm can be disrupted. Hence, the CFU obtained may be lower than the actual number of viable bacteria. Visualizing dead and live bacteria within the b...

Gonorrhea is a common sexually transmitted infection (STI)1. Neisseria gonorrhoeae (GC), a Gram-negative diplococcal bacterium, is the causative agent of this disease. Symptoms of genital infection can result in pain during urination, generalized genital pain, and urethral discharge. Infection is often asymptomatic2,3,4,5, and this allows for extended colonization. These untreated infections are a major health concern, as they have the potential to facilitate transmission of the organism and this can lead to complications such as pelvic inflammatory disease (PID) and disseminated gonococcal infection (DGI)6. Antibiotic-resistant gonorrhea is a major public health crisis and an increasing socioeconomic burden7. Reduced susceptibility to cephalosporins has resulted in treatment regimen change from a single antibiotic to dual therapy, which combines azithromycin or doxycycline with ceftriaxone8. The increased failure of ceftriaxone and azithromycin9,10, in combination with asymptomatic infections, highlights the need for understanding gonorrhea treatment failures.
The minimum inhibitory concentration (MIC) test, including agar dilution and disc diffusion tests, has been used as the standard medical test for identifying resistance to an antibiotic. Nevertheless, it is unclear if the MIC test reflects bacterial antibiotic resistance in vivo. The formation of bacterial biofilms contributes to the survival of bacteria in the presence of bactericidal concentrations of antibiotic: the MIC testing is unable to detect this effect11. Because GC can form biofilms on mucosal surfaces12, we hypothesize that antibiotic susceptibility within aggregates would be different from that seen in individual GC. Additionally, studies have shown that three phase variable surface molecules, Pili, opacity-associated protein (Opa), and lipooligosaccharides (LOS), that regulate inter-bacterium interactions, lead to different sized aggregates13,14,15. The contribution of these components to antibiotic resistance has not been examined due to the lack of proper methods.
Currently, there are several methods to measure biofilm eradication. The most widely used quantitative method is by measuring the changes in biomass using crystal violet staining16. However, the method requires significant experimental manipulation, which can potentially generate errors in experiment repeats17. The live/dead staining method used here allows visualization of live and dead bacteria and their distribution within the biofilm. However, the biofilm structure can pose as a physical barrier that reduces dye penetration. Therefore, to quantify live/dead bacteria within a group, the staining is limited to small biofilms or its precursor- microcolonies or aggregations. Other methods, including the agar dilution and disc diffusion tests, are not able to measure the effects of aggregation. To examine GC susceptibility within aggregation after antibiotic exposure, an ideal method would need to have both a quantitative assay that can measure live bacteria and visualize their distribution.
The procedure described here combines an ATP-utilization measurement and a live/dead staining assay to quantitatively and visually examine GC susceptibility within aggregates in the presence of antibiotics.

<table border="0" cellpadding="0" cellspacing="0" style="width:837px;" width="837">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">100x Kellogg&#39;s supplement</td>
			<td style="width:229px;"></td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Agar</td>
			<td style="width:229px;">United States Biological</td>
			<td style="width:119px;">A0930</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">BacTiter Assay&#160;</td>
			<td style="width:229px;">Promega</td>
			<td style="width:119px;">G8232</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Ceftriaxone</td>
			<td style="width:229px;">TCI</td>
			<td style="width:119px;">C2226</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Difco GC medium base&#160;</td>
			<td style="width:229px;">BD</td>
			<td style="width:119px;">228950</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ferric nitrate, nonahydrate&#160;</td>
			<td style="width:229px;">Sigma-Aldrich</td>
			<td style="width:119px;">254223-10G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glucose</td>
			<td style="width:229px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">BP350-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">L-glutamine Crystalline Powder</td>
			<td style="width:229px;">Fisher Scientific</td>
			<td style="width:119px;">BP379-100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">BacLight live/dead staining</td>
			<td style="width:229px;">Invitrogen</td>
			<td style="width:119px;">L7012</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MS11 Neisseria gonorrhoeae strain</td>
			<td style="width:229px;"></td>
			<td style="width:119px;"></td>
			<td>kindly provided by Dr. Herman Schneider, Walter Reed Army Institute for Research</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:323px;">Potassium phosphate dibasic (K2HPO4)</td>
			<td style="width:229px;">Fisher Scientific</td>
			<td style="width:119px;">P290-500</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">Potassium phosphate monobasic (KH2PO4)</td>
			<td style="width:229px;">Fisher Scientific</td>
			<td style="width:119px;">BP329-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Proteose Peptone&#160;</td>
			<td style="width:229px;">BD Biosciences</td>
			<td align="right" style="width:119px;">211693</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Sodium chloride (NaCl)</td>
			<td style="width:229px;">Fisher Scientific</td>
			<td style="width:119px;">S671-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Soluble Starch</td>
			<td style="width:229px;">Sigma-Aldrich</td>
			<td style="width:119px;">S9765</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thiamine pyrophosphate</td>
			<td style="width:229px;">Sigma-Aldrich</td>
			<td style="width:119px;">C8754-5G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Equipment</td>
			<td style="width:229px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Petri Dishes</td>
			<td style="width:229px;">VWR</td>
			<td style="width:119px;">25384-302</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">8-well coverslip-bottom chamber&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:119px;">155411</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">96-well tissue culture plates&#160;</td>
			<td>Corning, Falcon</td>
			<td style="width:119px;">3370</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:323px;">Biosafety Cabinet (NU-425-600 Class II, A2 Laminar Flow Biohazard Hood)</td>
			<td style="width:229px;">Nuaire</td>
			<td style="width:119px;">32776</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:323px;">CO2 Incubator</td>
			<td style="width:229px;">Fisher Scientific</td>
			<td style="width:119px;">&#160;Model 3530</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:323px;">Confocal microscope equipped with live imaging chamber</td>
			<td style="width:229px;">Leica</td>
			<td style="width:119px;">SP5X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Corning&#160; 96 Well Black Polystyrene Microplate&#160;</td>
			<td style="width:229px;">Corning</td>
			<td style="width:119px;">3904</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Glomax Illuminator&#160;</td>
			<td style="width:229px;">Promega</td>
			<td style="width:119px;">E6521</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Pipette tips (0.1-10 &#181;L)</td>
			<td style="width:229px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">02-717-133</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pipette tips (1000 &#181;L)</td>
			<td>VWR</td>
			<td style="width:119px;">83007-382</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Pipette tips (200 &#181;L)</td>
			<td style="width:229px;">VWR</td>
			<td style="width:119px;">53509-007</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Spectrophotometer Ultrospec 2000 UV</td>
			<td style="width:229px;">Pharmacia Biotech</td>
			<td style="width:119px;">80-2106-00</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Sterile 15 ml conical tubes</td>
			<td style="width:229px;">VWR</td>
			<td style="width:119px;">21008-216</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Sterile Microcentrifuge Tubes (1.7 mL)</td>
			<td style="width:229px;">Sorenson BioScience</td>
			<td style="width:119px;">16070</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sterile polyester-tipped applicators</td>
			<td>Fisher Scientific</td>
			<td>23-400-122</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:323px;">Sonicator</td>
			<td style="width:229px;">Kontes</td>
			<td style="width:119px;">Equivelent to 9110001</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantitative examination of antibiotic susceptibility of neisseria gonorrhoeae aggregates using atp-utilization commercial assays and live/dead staining

The emergence of antibiotic resistant Neisseria gonorrhoeae (GC) is a worldwide health threat and highlights the need to identify individuals who fail treatment. This Gram-negative bacterium causes gonorrhea exclusively in humans. During infection, it is able to form aggregates and/or biofilms. The minimum inhibitory concentration (MIC) test is used for to determine susceptibility to antibiotics and to define appropriate treatment. However, the mechanism of the eradication in vivo and its relationship to laboratory results are not known. A method that examines how GC aggregation affects antibiotic susceptibility and shows the relationship between aggregate size and antibiotic susceptibility was developed. When GC aggregate, they are more resistant to antibiotic killing, with bacteria in the center surviving ceftriaxone treatment better than those in the periphery. The data indicate that N. gonorrhoeae aggregation can reduce its susceptibility to ceftriaxone, which is not reflected using the standard agar plate-based MIC methods. The method used in this study will allow researchers to test bacterial susceptibility under clinically relevant conditions.

Two methods were employed: an ATP utilization assay and a live/dead staining assay. The results can either be combined or individually used for examining bacterial survival within aggregates after antibiotic treatment. The ATP utilization assay has been shown to measure accurately viable bacteria in S. aureus biofilms20,21. Here, MS11Opa+Pil+ strain was used to examine the role of GC aggregation in antibiotic susceptibili...

Watch this Scientific Journal Video about Quantitative Examination of Antibiotic Susceptibility of Neisseria gonorrhoeae Aggregates Using ATP-utilization Commercial Assays and Live/Dead Staining at Jo

Quantitative Examination of Antibiotic Susceptibility of Neisseria gonorrhoeae Aggregates Using ATP-utilization Commercial Assays and Live/Dead Staining

A simple ATP-measuring assay and live/dead staining method were used to quantify and visualize Neisseria gonorrhoeae survival after treatment with ceftriaxone. This protocol can be extended to examine the antimicrobial effects of any antibiotic and can be used to define the minimal inhibitory concentration of antibiotics in bacterial biofilms.

Quantitative Examination of Antibiotic Susceptibility of Neisseria gonorrhoeae Aggregates Using ATP-utilization Commercial Assays and Live/Dead Staining

The emergence of antibiotic resistant Neisseria gonorrhoeae (GC) is a worldwide health threat and highlights the need to identify individuals who fail ...

This technique allows us to measure antibiotic susceptibility under more clinically relevant conditions. The technique also allows us to determine the true antibiotic concentration that can kill bacteria in aggregates. This technique can be applied to determining the concentration needed for eliminating GC aggregates.The method can also be applied to measuring the antimicrobial susceptibility of any bacteria that is able to form aggregates. Pay careful attention to the lysis steps to ensure the lysis is complete. Otherwise the ATP measuring assay will underestimate the number of viable bacteria.Visualization of this method will allow other researchers to follow and replicate this experiment with consistency. Begin by streaking Neisseria gonorrhoeae, or GC strains, on GCK agar supplemented with 1%Kellogg for a 16 to 18-hour incubation at 37 degrees Celsius and 5%carbon dioxide. The next morning, use a light microscope to carefully select pili-negative colonies without dark edges or pili-positive colonies with dark edges from each plate, and streak the picked colonies onto new GCK plates for a 16 to 18-hour culture at 37 degrees Celsius and 5%carbon dioxide.The next morning, use a sterile applicator to collect GC colonies from each plate and resuspend each swab in warm broth supplemented with 4.2%sodium bicarbonate and 1%Kellogg solution. Measure the optical density at 650 nanometers, or OD650, to determine the concentration of the suspended bacteria and adjust the GC concentration to about one times 10 to the eight colony forming units per milliliter. Next, add 99 microliters of the GC suspension into individual wells of a 96-well plate and allow the bacteria to aggregate at 37 degrees Celsius and 5%carbon dioxide for six hours.At the end of the incubation, add one microliter of serially diluted ceftriaxone to each well leaving some wells untreated to serve as controls and return the plate to the incubator for another 24 hours. The next day, sonicate the suspension in each well three times at 144 watts and 20 kilohertz for five seconds per sonication and add 100 microliters of commercially available ATP utilization glow reagent to each well. Carefully transfer 150 microliters of mixture from each well into individual wells of a new 96-well black microplate and measure the absorbance of each well at 560 nanometers on a plate reader.Then, calculate the survival rate by the ratio of the reading obtained after serial antibiotic treatment to the reading from the untreated wells. For visualization of the live/dead GC aggregates, use a sterile applicator to collect GC from the overnight cultured plates and resuspend the GC in prewarmed GCP medium supplemented with 1%Kellogg. Measure the OD650 by spectrophotometry and adjust the concentration to approximately one times 10 to the seven colony-forming units per milliliter.Next, add 198 microliters of GC suspension into eight-well coverslip-bottom chambers and incubate the chambers at 37 degrees Celsius and 5%carbon dioxide for six hours. At the end of the incubation, treat the bacteria with two microliters of ceftriaxone per aggregation condition and return the chambers to the incubator for the appropriate experimental incubation period. At the end of the incubation, add 0.6 microliters of live/dead staining solution into each well and return the chambers to the incubator for an additional 20 minutes.Then, use a confocal microscope to obtain z-series images. For measurement of the size of the GC aggregates, open the first image in ImageJ and select freehand lines to circle the area of each aggregation in the image. Click analyze and measure.The size of the aggregates will be indicated under the area column. For quantification of the fluorescence intensity ratio of the live to dead staining in each aggregate, click analyze and set measurements and check the integrated density in the popup window. Click OK and click image, color and channels tool.Select color and channel one as the fluorescence for dead bacteria staining. Select freehand lines to circle the area of each aggregation and click analyze and measure to obtain the fluorescence intensity ratio for each aggregate in the integrated density column. Select channel two for the fluorescence for the live bacterial staining and measure the fluorescence intensity in each aggregate as just demonstrated.Then divide the live fluorescence intensity data by the dead fluorescence intensity data to obtain the live to dead fluorescence intensity ratio. In this representative experiment, nonaggregated pili positive, aggregated pili positive or aggregated and disrupted pili positive bacteria were treated with serial dilutions of ceftriaxone before measurement of their ATP levels. Preaggregated GC demonstrated a significantly higher survival than non-aggregated or aggregation disrupted GC when treated with equal concentrations of ceftriaxone or higher.Pili-positive strains that form larger aggregates exhibited the highest ATP levels after ceftriaxone treatment compared to the mutant strains. Regardless of strain tested, live/dead staining before antibiotic treatment revealed dead bacteria largely located at the outer layers of the culture, while live GC were identified mainly within the core of ceftriaxone-treated aggregates. As expected, pili-positive bacteria formed the largest aggregates, while pili-negative cultures formed the smallest.Notably, pili-positive aggregates were still alive in their core layers after antibiotic treatment, whereas GC in the small, loose mutant aggregates were dead. Based on the size and survival of the GC, a correlation graph can be plotted to examine the relationship between the aggregation size and antibiotic survival of the bacteria. Sonication is important for making sure that ATP from each individual bacterium is released within the tightly bound aggregates.Otherwise, the measurements will not be consistent. It is important to plate the bacteria after they aggregate and are treated with antibiotics to measure both the viable and the replication-capable bacteria. The technique measures the bacteria aggregation influence on antibiotic susceptibility allowing researchers to develop better drugs for treating diseases.

quantitative-examination-antibiotic-susceptibility-neisseria

Research

JoVE Journal

Immunology and Infection

Examination of the Telomere G-overhang Structure in Trypanosoma brucei

The telomere G-overhang structure has been identified in many eukaryotes including yeast, vertebrates, and Trypanosoma brucei. It serves as the substrate for telomerase for de novo telomere DNA synthesis and is therefore important for telomere maintenance. T. brucei is a protozoan parasite that causes sleeping sickness in humans and nagana in cattle. Once infected mammalian host, T. brucei cell regularly switches its surface antigen to evade the host's immune attack. We have recently demonstrated that the T. brucei telomere structure plays an essential role in regulation of surface antigen gene expression, which is critical for T. brucei pathogenesis. However, T. brucei telomere structure has not been extensively studied due to the limitation of methods for analysis of this specialized structure. We have now successfully adopted the native in-gel hybridization and ligation-mediated primer extension methods for examination of the telomere G-overhang structure and an adaptor ligation method for determination of the telomere terminal nucleotide in T. brucei cells. Here, we will describe the protocols in detail and compare their different advantages and limitations.

Examination of the Telomere G-overhang Structure in Trypanosoma brucei

Telomeres are essential for chromosome stability and the telomere G-overhang structure is essential for telomerase-mediated telomere maintenance. We have recently adopted two methods for detecting the telomere G-overhang structure in Trypanosoma brucei, which are native in-gel hybridization and ligation-mediated primer extension, which will be described.

The telomere G-overhang structure has been identified in many eukaryotes including yeast, vertebrates, and Trypanosoma brucei. It serves as the substrate ...

Visualisation and Quantification of Intracellular Interactions of Neisseria meningitidis and Human &alpha;-actinin by Confocal Imaging

The Opc protein of Neisseria meningitidis (Nm, meningococcus) is a surface-expressed integral outer membrane protein, which can act as an adhesin and an effective invasin for human epithelial and endothelial cells. We have identified endothelial surface-located integrins as major receptors for Opc, a process which requires Opc to first bind to integrin ligands such as vitronectin and via these to the cell-expressed receptors1. This process leads to bacterial invasion of endothelial cells2. More recently, we observed an interaction of Opc with a 100kDa protein found in whole cell lysates of human cells3. We initially observed this interaction when host cell proteins separated by electrophoresis and blotted on to nitrocellulose were overlaid with Opc-expressing Nm. The interaction was direct and did not involve intermediate molecules. By mass spectrometry, we established the identity of the protein as &alpha;-actinin. As no surface expressed &alpha;-actinin was found on any of the eight cell lines examined, and as Opc interactions with endothelial cells in the presence of serum lead to bacterial entry into the target cells, we examined the possibility of the two proteins interacting intracellularly. For this, cultured human brain microvascular endothelial cells (HBMECs) were infected with Opc-expressing Nm for extended periods and the locations of internalised bacteria and &alpha;-actinin were examined by confocal microscopy. We observed time-dependent increase in colocalisation of Nm with the cytoskeletal protein, which was considerable after an eight hour period of bacterial internalisation. In addition, the use of quantitative imaging software enabled us to obtain a relative measure of the colocalisation of Nm with &alpha;-actinin and other cytoskeletal proteins. Here we present a protocol for visualisation and quantification of the colocalisation of the bacterium with intracellular proteins after bacterial entry into human endothelial cells, although the procedure is also applicable to human epithelial cells.

Visualisation and Quantification of Intracellular Interactions of Neisseria meningitidis and Human &amp;#945;-actinin by Confocal Imaging

Neisseria meningitidis (Nm), a gram negative human-specific respiratory pathogen, can bind to human &alpha;-actinin. Here we present a protocol for visualisation of colocalisation of the bacterium with intracellular &alpha;-actinin after bacterial entry into human brain microvascular endothelial cells (HBMECs).

The Opc protein of Neisseria meningitidis (Nm, meningococcus) is a surface-expressed integral outer membrane protein, which can act as an adhesin and an ...

Quantitative Analyses of all Influenza Type A Viral Hemagglutinins and Neuraminidases using Universal Antibodies in Simple Slot Blot Assays

Hemagglutinin (HA) and neuraminidase (NA) are two surface proteins of influenza viruses which are known to play important roles in the viral life cycle and the induction of protective immune responses1,2. As the main target for neutralizing antibodies, HA is currently used as the influenza vaccine potency marker and is measured by single radial immunodiffusion (SRID)3. However, the dependence of SRID on the availability of the corresponding subtype-specific antisera causes a minimum of 2-3 months delay for the release of every new vaccine. Moreover, despite evidence that NA also induces protective immunity4, the amount of NA in influenza vaccines is not yet standardized due to a lack of appropriate reagents or analytical method5. Thus, simple alternative methods capable of quantifying HA and NA antigens are desirable for rapid release and better quality control of influenza vaccines.
Universally conserved regions in all available influenza A HA and NA sequences were identified by bioinformatics analyses6-7. One sequence (designated as Uni-1) was identified in the only universally conserved epitope of HA, the fusion peptide6, while two conserved sequences were identified in neuraminidases, one close to the enzymatic active site (designated as HCA-2) and the other close to the N-terminus (designated as HCA-3)7. Peptides with these amino acid sequences were synthesized and used to immunize rabbits for the production of antibodies. The antibody against the Uni-1 epitope of HA was able to bind to 13 subtypes of influenza A HA (H1-H13) while the antibodies against the HCA-2 and HCA-3 regions of NA were capable of binding all 9 NA subtypes. All antibodies showed remarkable specificity against the viral sequences as evidenced by the observation that no cross-reactivity to allantoic proteins was detected. These universal antibodies were then used to develop slot blot assays to quantify HA and NA in influenza A vaccines without the need for specific antisera7,8. Vaccine samples were applied onto a PVDF membrane using a slot blot apparatus along with reference standards diluted to various concentrations. For the detection of HA, samples and standard were first diluted in Tris-buffered saline (TBS) containing 4M urea while for the measurement of NA they were diluted in TBS containing 0.01% Zwittergent as these conditions significantly improved the detection sensitivity. Following the detection of the HA and NA antigens by immunoblotting with their respective universal antibodies, signal intensities were quantified by densitometry. Amounts of HA and NA in the vaccines were then calculated using a standard curve established with the signal intensities of the various concentrations of the references used. 
Given that these antibodies bind to universal epitopes in HA or NA, interested investigators could use them as research tools in immunoassays other than the slot blot only.

A simple slot blot method was developed for the quantification of influenza viral hemagglutinin and neuraminidase using universal antibodies targeting their most conserved sequences identified through bioinformatics analyses. This innovative approach may provide a useful alternative to quantitative determination of all viral hemagglutinin and neuraminidase.

Hemagglutinin (HA) and neuraminidase (NA) are two surface proteins of influenza viruses which are known to play important roles in the viral life cycle ...

Preparation of a Blood Culture Pellet for Rapid Bacterial Identification and Antibiotic Susceptibility Testing

Bloodstream infections and sepsis are a major cause of morbidity and mortality. The successful outcome of patients suffering from bacteremia depends on a rapid identification of the infectious agent to guide optimal antibiotic treatment. The analysis of Gram stains from positive blood culture can be rapidly conducted and already significantly impact the antibiotic regimen. However, the accurate identification of the infectious agent is still required to establish the optimal targeted treatment. We present here a simple and fast bacterial pellet preparation from a positive blood culture that can be used as a sample for several essential downstream applications such as identification by MALDI-TOF MS, antibiotic susceptibility testing (AST) by disc diffusion assay or automated AST systems and by automated PCR-based diagnostic testing. The performance of these different identification and AST systems applied directly on the blood culture bacterial pellets is very similar to the performance normally obtained from isolated colonies grown on agar plates. Compared to conventional approaches, the rapid acquisition of a bacterial pellet significantly reduces the time to report both identification and AST. Thus, following blood culture positivity, identification by MALDI-TOF can be reported within less than 1 hr whereas results of AST by automated AST systems or disc diffusion assays within 8 to 18 hr, respectively. Similarly, the results of a rapid PCR-based assay can be communicated to the clinicians less than 2 hr following the report of a bacteremia. Together, these results demonstrate that the rapid preparation of a blood culture bacterial pellet has a significant impact on the identification and AST turnaround time and thus on the successful outcome of patients suffering from bloodstream infections.

A rapid bacterial pellet preparation from a positive blood culture can be used as a sample for applications such as identification by MALDI-TOF, Gram staining, antibiotic susceptibility testing and PCR-based test. The results can be rapidly communicated to clinicians to improve the outcome of patients suffering from bloodstream infections.

Bloodstream infections and sepsis are a major cause of morbidity and mortality. The successful outcome of patients suffering from bacteremia depends on a ...

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 ...

Examination of Host Phenotypes in Gambusia affinis Following Antibiotic Treatment

The commonality of antibiotic usage in medicine means that understanding the resulting consequences to the host is vital. Antibiotics often decrease host microbiome community diversity and alter the microbial community composition. Many diseases such as antibiotic-associated enterocolitis, inflammatory bowel disease, and metabolic disorders have been linked to a disrupted microbiota. The complex interplay between host, microbiome, and antibiotics needs a tractable model for studying host-microbiome interactions. Our freshwater vertebrate fish serves as a useful model for investigating the universal aspects of mucosal microbiome structure and function as well as analyzing consequential host effects from altering the microbial community. Methods include host challenges such as infection by a known fish pathogen, exposure to fecal or soil microbes, osmotic stress, nitrate toxicity, growth analysis, and measurement of gut motility. These techniques demonstrate a flexible and useful model system for rapid determination of host phenotypes.

Examination of Host Phenotypes in Gambusia affinis Following Antibiotic Treatment

This study involves methods to reveal effects on a model fish host following alteration of the skin and gut microbiome communities&#160;composition by an antibiotic.

The commonality of antibiotic usage in medicine means that understanding the resulting consequences to the host is vital. Antibiotics often decrease host ...

Quantitative Polymerase Chain Reaction-based Analyses of Murine Intestinal Microbiota After Oral Antibiotic Treatment

The gut microbiota has a central influence on human health. Microbial dysbiosis is associated with many common immunopathologies such as inflammatory bowel disease, asthma and arthritis. Thus, understanding the mechanisms underlying microbiota-immune system crosstalk is of crucial importance. Antibiotic administration, while aiding pathogen clearance, also induces drastic changes in the size and composition of intestinal bacterial communities which can have an impact on human health. Antibiotic treatment in mice recapitulates the impact and long-term changes in human microbiota from antibiotic treated patients, and enables investigation of the mechanistic links between changes in microbial communities and immune cell function. While several methods for antibiotic treatment of mice have been described, some of them induce severe dehydration and weight-loss complicating the interpretation of the data. Here, we provide two protocols for oral antibiotic administration which can be used for long-term treatment of mice without inducing major weight-loss. These protocols make use of a combination of antibiotics that target both Gram-positive and Gram-negative bacteria and can be provided either ad libitum in the drinking water or by oral gavage. Moreover, we describe a method for the quantification of microbial density in fecal samples by qPCR which can be used to validate the efficacy of the antibiotic treatment. The combination of these approaches provides a reliable methodology for the manipulation of the intestinal microbiota and the study of the effects of antibiotic treatment in mice.

Here we provide detailed protocols for the oral administration of antibiotics to mice, collection of fecal samples, DNA extraction and quantification of fecal bacteria by qPCR.

The gut microbiota has a central influence on human health. Microbial dysbiosis is associated with many common immunopathologies such as inflammatory ...

Antibiotic Dereplication Using the Antibiotic Resistance Platform

One of the main challenges in the search for new antibiotics from natural product extracts is the re-discovery of common compounds. To address this challenge, dereplication, which is the process of identifying known compounds, is performed on samples of interest. Methods for dereplication such as analytical separation followed by mass spectrometry are time-consuming and resource-intensive. To improve the dereplication process, we have developed the antibiotic resistance platform (ARP). The ARP is a library of approximately 100 antibiotic resistance genes that have been individually cloned into Escherichia coli. This strain collection has many applications, including a cost-effective and facile method for antibiotic dereplication. The process involves the fermentation of antibiotic-producing microbes on the surface of rectangular Petri dishes containing solid medium, thereby allowing for the secretion and diffusion of secondary metabolites through the medium. After a 6 day fermentation period, the microbial biomass is removed, and a thin agar-overlay is added to the Petri dish to create a smooth surface and enable the growth of the E. coli indicator strains. Our collection of ARP strains is then pinned onto the surface of the antibiotic-containing Petri dish. The plate is next incubated overnight to allow for E. coli growth on the surface of the overlay. Only strains containing resistance to a specific antibiotic (or class) grow on this surface enabling rapid identification of the produced compound. This method has been successfully used for the identification of producers of known antibiotics and as a means to identify those producing novel compounds.

We describe a platform that utilizes a library of isogenic antibiotic resistant Escherichia coli for the dereplication of antibiotics. The identity of an antibiotic produced by bacteria or fungi can be deduced by the growth of E. coli expressing its respective resistance gene. This platform is economically effective and time-efficient.

One of the main challenges in the search for new antibiotics from natural product extracts is the re-discovery of common compounds. To address this ...

Visualization of Bacterial Resistance using Fluorescent Antibiotic Probes

Fluorescent antibiotics are multipurpose research tools that are readily used for the study of antimicrobial resistance, due to their significant advantage over other methods. To prepare these probes, azide derivatives of antibiotics are synthesized, then coupled with alkyne-fluorophores using azide-alkyne dipolar cycloaddition by click chemistry. Following purification, the antibiotic activity of the fluorescent antibiotic is tested by minimum inhibitory concentration assessment. In order to study bacterial accumulation, either spectrophotometry or flow cytometry may be used, allowing for much simpler analysis than methods relying on radioactive antibiotic derivatives. Furthermore, confocal microscopy can be used to examine localization within the bacteria, affording valuable information about mode of action and changes that occur in resistant species. The use of fluorescent antibiotic probes in the study of antimicrobial resistance is a powerful method with much potential for future expansion.

Fluorescently tagged antibiotics are powerful tools that can be used to study multiple aspects of antimicrobial resistance. This article describes the preparation of fluorescently tagged antibiotics and their application to studying antibiotic resistance in bacteria. Probes can be used to study mechanisms of bacterial resistance (e.g., efflux) by spectrophotometry, flow cytometry, and microscopy.