1. Blood Culture Broths Flag as &#8220;Positive&#8221;
<ol>
	<li>Remove the signaled blood culture bottle from the continuous monitoring incubation cabinet and place it into a biological safety cabinet. Note: Bottles can contain hazardous microorganisms and universal precautions need to be followed. Due to the risk of infectious aerosols in sampling, all sampling procedures must be performed in a Biosafety Class II laminar flow cabinet.</li>
</ol>
2. Gram Stain is Prepared
<ol>
	<li>Prepare a Gram stain from the signaled blood culture broth as per local institutional protocols. Note: When Gram negative organisms are identified on microscopy the blood culture broth is processed as per the following method. When Gram positive organisms are identified, an alternative molecular method targeting genetic identification and resistance markers is applied to the broth (not addressed in this article)13.</li>
</ol>
3. Transfer of Flagged Blood Culture Broth to a Serum Separating Tube
<ol>
	<li>Gently mix the blood culture bottle by inverting 2-3x.</li>
	<li>Within the biosafety cabinet attach a 10&#160;ml&#160;syringe to a safety blood transfer device.</li>
	<li>Attach the blood transfer device to the blood culture bottle and withdraw 5 ml&#160;of the broth into the syringe. Transfer the aspirated BC broth into a serum separating tube.</li>
</ol>
4. Concentration of Blood Culture Broth
<ol>
	<li>Centrifuge the serum separating tube at 1,250 x g for 15 min&#160;which removes a large volume of red blood cells.</li>
	<li>Aspirate and discard the supernatant using a sterile transfer pipette being careful to leave approximately 1 ml&#160;of the buffy coat immediately above the gel/fluid interface. Note: The aerobic bottles show a clear separation of red blood cells to the bottom of the tube with the gel/fluid interface appearing an opaque white color. In contrast, when applied to the lytic anaerobic blood culture broth the gel/fluid interface appears as a deep red color due to the lysed red blood cell components remaining suspended in the supernatant.</li>
</ol>
5. Repeat Centrifugation Wash Steps
<ol>
	<li>Gently mix the last 1 ml&#160;of buffy coat fluid above the gel interface with a sterile pipette and then transfer the entire volume into a 1.5&#160;ml&#160;microcentrifuge tube. Centrifuge the new tube at 288 x g for 30 sec.</li>
	<li>Transfer the supernatant using a plastic disposable 1&#160;ml&#160;transfer pipette into a new 1.5&#160;ml&#160;microcentrifuge tube and discard the tube with the pellet. Note: It is critical in this step that care is taken to avoid the transfer of the pellet. This is particularly important for a specimen being processed from the anaerobic BC bottle as the supernatant remains pigmented and the pellet is not always clearly seen.</li>
</ol>
6. Lysis of Residual Cells
<ol>
	<li>Centrifuge the specimen at 18,407 x g for 1 min&#160;and then aspirate (and discard) the supernatant using a fine tipped transfer pipette to leave as little residual liquid as possible without disrupting the pellet.</li>
	<li>Resuspend the residual pellet in 1 ml&#160;of sterile DNAse and RNAse free water by pipetting up and down. Note: Some authors have described the use of alcohol solutions in place of sterile water to resuspend the pellet which renders bacteria non-viable.</li>
	<li>Centrifuge the resuspended solution at 18,407 x g for 1 min.</li>
</ol>
7. Extraction of Bacterial Proteins
<ol>
	<li>Aspirate and discard the supernatant, again using aspiration with a fine tip pipette ensuring that as much liquid as possible is removed.</li>
	<li>Resuspend the pellet in 10 &#181;l&#160;formic acid (70% v/v). Note: Formic acid can affect the body if it is inhaled or if it comes into contact with skin. When preparing or manipulating solutions it is recommended that staff use a fume cabinet in addition to personal protective equipment.</li>
	<li>Mix well using the pipette to ensure a homogenous resuspended solution. Using the pipette tip to physically disrupt the pellet may be necessary to ensure a more homogenous solution.</li>
</ol>
8. Preparation of MALDI-TOF Target Plate
<ol>
	<li>Inoculate a clean MALDI-TOF target plate with 2 &#181;l&#160;of the prepared suspension per target spot. Prepare 3 target sites for each sample to overcome the occasional problem of failed reads.</li>
	<li>Allow the MALDI-TOF target plate to dry. The rate of drying can be increased by placing the plate on the edge of the fume hood to maximize air flow across the plate.</li>
	<li>Overlay each dried spot with 1 &#181;l&#160;of the matrix solution (10 mg/ml &#945;-cyano-4-hydroxycinnamic acid (HCCA), 50% acetonitrile, 2.5% trifluoroacetic acid). Note: Matrix solution can affect the body if it is inhaled or if it comes into contact with skin. When preparing or manipulating solutions it is recommended that staff use a fume cabinet in addition to personal protective equipment.</li>
	<li>Allow the MALDI-TOF target plate to dry on the edge of the fume cupboard as described above. Ensure a homogenous preparation fills each of the target spots on the plate.</li>
</ol>
9. Place MALDI-TOF Target Plate into the Mass Spectrometer
<ol>
	<li>Insert the MALDI-TOF target plate into the MALDI-TOF mass spectrometer. Ensure the plate is sitting flush with the spring-loaded plates. Note: do not insert the target plate until all target spots are dry.</li>
	<li>Ensure the rubber seal is clean of lint, dust and hair to allow the required vacuum conditions can be created.</li>
	<li>Close the MALDI-TOF stage lid and then press the &#8220;in/out&#8221; button on the front of the instrument. The lid will now lock and allow the necessary vacuum to be created.</li>
</ol>
10. MALDI-TOF MS Spectra Acquisition
<ol>
	<li>Open the MALDI Biotyping and FlexControl software.</li>
	<li>Within the Typing software select &#8220;new classification&#8221; from the dropdown menu titled &#8220;file&#8221;. Name the project and then select &#8220;new&#8221;. Select &#8220;Next&#8221; to complete the setup within the Typing software.</li>
	<li>Within the Control software window identify the on-screen graphic of the target plate. Highlight the MALDI-TOF target spots that are in use by moving the mouse over the inoculated spots while holding down the left mouse button.</li>
	<li>Use the right mouse button to click anywhere on the selected target positions and then select &#8220;add Analytes&#8221; from the dropdown menu.</li>
	<li>Add blood culture identification details to the &#8220;ID&#8221; column for each of the target spots and click &#8220;next&#8221; when complete.</li>
	<li>Select the commercial &#8220;taxonomy&#8221; spectra database and select &#8220;next&#8221;. Note: Laboratories may utilize additional in-house or commercial databases to increase the number of reference spectra.</li>
	<li>Click &#8220;finish&#8221; and the MALDI-TOF MS will commence generating spectra. Note: MALDI-TOF settings were as per manufacture&#8217;s settings (linear positive mode, 60 Hz laser frequency, 20 kV acceleration voltage, 16.7 kV IS2 voltage, 170 nsec extraction delay, and 2,000-20,137 m/z range).</li>
	<li>If the MALDI Control software fails to generate peaks, manual acquisition of spectra may be performed (method not described).</li>
</ol>
11. Post Analysis&#160;Interpretation of MALDI-TOF MS Scores
<ol>
	<li>Once the spectra are acquired and analysis is complete, select the &#8220;+&#8221; button next to species identification on the Typing software to expand the identification list for each target.</li>
	<li>Study the top 5 identifications, noting if the top 5 are similar. Discordant top 5 genera with scores &#8805;1.7 of the same target spot raised the possibility of mixed broths. Note: MALDI-TOF technology has poor sensitivity for detection of mixed broths. For example, when a broth contains mixed species a high confidence score may be identified for just one of the mixed species.</li>
	<li>When a score &#8805; 2.0 is noted for the highest match on a target spot, report the species.</li>
	<li>When the highest score on a target spot is &#8805;1.7, but &#60; 2.0, report the genera only. If additional criteria of the top 5 identifications are concordant, then report to species level.</li>
</ol>
12. Removal of MALDI-TOF Target Plate
<ol>
	<li>When all spectra are complete press the &#8220;in/out&#8221; button on the MALDI-TOF machine.</li>
	<li>Open the MALDI-TOF target plate receptacle and remove the MALDI-TOF target plate.</li>
	<li>If using a reusable MALDI-TOF target plate, clean all target spots using alcohol and store the MALDI-TOF plate at RT once it is clean and dry.</li>
</ol>

<ol>
	<li>Bearman, G. M., Wenzel, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bacteremias:+a+leading+cause+of+death.">Bacteremias: a leading cause of death.</a> Arch. Med. Res. 36 (6), 646-659 (2005).</li><li>Leibovici, L., Shraga, I., Drucker, M., Konigsberger, H., Samra, Z., Pitlik, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+benefit+of+appropriate+empirical+antibiotic+treatment+in+patients+with+bloodstream+infection.">The benefit of appropriate empirical antibiotic treatment in patients with bloodstream infection.</a> J. Intern. Med. 244 (5), 379-386 (1998).</li><li>Kumar, 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=Duration+of+hypotension+before+initiation+of+effective+antimicrobial+therapy+is+the+critical+determinant+of+survival+in+human+septic+shock.">Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock.</a> Crit. Care Med. 34 (6), 1589-1596 (2006).</li><li>Munson, E. L., Diekema, D. J., Beekmann, S. E., Chapin, K. C., Doern, G. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+and+treatment+of+bloodstream+infection:+laboratory+reporting+and+antimicrobial+management.">Detection and treatment of bloodstream infection: laboratory reporting and antimicrobial management.</a> J. Clin. Microbiol. 41 (1), 495-497 (2003).</li><li>Clerc, O., Prod'hom, G., Vogne, C., Bizzini, A., Calandra, T., Greub, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+Matrix-Assisted+Laser+Desorption+Ionization+Time-of-Flight+Mass+Spectrometry+on+the+Clinical+Management+of+Patients+With+Gram-negative+Bacteremia:+A+Prospective+Observational+Study.">Impact of Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry on the Clinical Management of Patients With Gram-negative Bacteremia: A Prospective Observational Study.</a> Clin. Infect. Dis. 56 (8), 1101-1107 (2013).</li><li>Dekker, J. P., Branda, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> MALDI-TOF Mass Spectrometry in the Clinical Microbiology Laboratory. Clinical Microbiology Newslette. 33 (12), 87-93 (2011).</li><li>Seng, 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=Ongoing+revolution+in+bacteriology:+routine+identification+of+bacteria+by+matrix-assisted+laser+desorption+ionization+time-of-flight+mass+spectrometry.">Ongoing revolution in bacteriology: routine identification of bacteria by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.</a> Clin. Infect. Dis. 49 (4), 543-551 (2009).</li><li>Neville, S. 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=Utility+of+matrix-assisted+laser+desorption+ionization-time+of+flight+mass+spectrometry+following+introduction+for+routine+laboratory+bacterial+identification.">Utility of matrix-assisted laser desorption ionization-time of flight mass spectrometry following introduction for routine laboratory bacterial identification.</a> J. Clin. Microbiol. 49 (8), 2980-2984 (2011).</li><li>Schmidt, V., Jarosch, A., M&#228;rz, P., Sander, C., Vacata, V., Kalka-Moll, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+identification+of+bacteria+in+positive+blood+culture+by+matrix-assisted+laser+desorption+ionization+time-of-flight+mass+spectrometry.">Rapid identification of bacteria in positive blood culture by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.</a> Eur. J. Clin. Microbiol. Infect. Dis. 31 (3), 311-317 (2012).</li><li>March-Rossell&#243;, G. A., Mu&#241;oz-Moreno, M. F., de Urri&#233;s, M. C., Bratos-P&#233;rez, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+differential+centrifugation+protocol+and+validation+criterion+for+enhancing+mass+spectrometry+(MALDI-TOF)+results+in+microbial+identification+using+blood+culture+growth+bottles.">A differential centrifugation protocol and validation criterion for enhancing mass spectrometry (MALDI-TOF) results in microbial identification using blood culture growth bottles.</a> Eur. J. Clin. Microbiol. Infect. Dis. 32 (5), 699-704 (2012).</li><li>Christner, M., Rohde, H., Wolters, M., Sobottka, I., Wegscheider, K., Aepfelbacher, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+identification+of+bacteria+from+positive+blood+culture+bottles+by+use+of+matrix-assisted+laser+desorption-ionization+time+of+flight+mass+spectrometry+fingerprinting.">Rapid identification of bacteria from positive blood culture bottles by use of matrix-assisted laser desorption-ionization time of flight mass spectrometry fingerprinting.</a> J. Clin. Microbiol. 48 (5), 1584-1591 (2010).</li><li>Gray, T. J., Thomas, L., Olma, T., Iredell, J. R., Chen, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+identification+of+Gram-negative+organisms+from+blood+culture+bottles+using+a+modified+extraction+method+and+MALDI-TOF+mass+spectrometry.">Rapid identification of Gram-negative organisms from blood culture bottles using a modified extraction method and MALDI-TOF mass spectrometry.</a> Diagn. Microbiol. Infect. Dis. 72 (2), 110-112 (2013).</li><li>Hazelton, B. J., Thomas, L. C., Unver, T., Iredell, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+identification+of+Gram-positive+pathogens+and+their+resistance+genes+from+positive+blood+culture+broth+using+a+multiplex+tandem+RT-PCR+assay.">Rapid identification of Gram-positive pathogens and their resistance genes from positive blood culture broth using a multiplex tandem RT-PCR assay.</a> J. Med. Microbiol. 62 (2), 223-2231 (2013).</li><li>Saffert, R. T., Cunningham, S. A., Mandrekar, J., Patel, R. <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+three+preparatory+methods+for+detection+of+bacteremia+by+MALDI-TOF+mass+spectrometry.">Comparison of three preparatory methods for detection of bacteremia by MALDI-TOF mass spectrometry.</a> Diagn. Microbiol. Infect. Dis. 73 (1), 21-26 (2012).</li><li>Consoir, C., L&#246;rch, D., Schneider, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+identification+of+bacteria+from+charcoal-containing+blood+culture+bottles+using+matrix-assisted+laser+desorption/ionisation+time-of-flight+mass+spectrometry.">Direct identification of bacteria from charcoal-containing blood culture bottles using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.</a> Eur. J. Clin. Microbiol. Infect. Dis. 31 (10), 2843-2850 (2012).</li><li>Martiny, D., Dediste, A., Vandenberg, O. <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+an+in-house+method+and+the+commercial+Sepsityper&#8482;+kit+for+bacterial+identification+directly+from+positive+blood+culture+broths+by+matrix-assisted+laser+desorption-ionisation+time-of-flight+mass+spectrometry.">Comparison of an in-house method and the commercial Sepsityper&#8482; kit for bacterial identification directly from positive blood culture broths by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry.</a> Eur. J. Clin. Microbiol. Infect. Dis. 31 (9), 2269-2281 (2012).</li><li>Moussaoui, 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=Matrix-assisted+laser+desorption+ionization+time-of-flight+mass+spectrometry+identifies+90%+of+bacteria+directly+from+blood+culture+vials.">Matrix-assisted laser desorption ionization time-of-flight mass spectrometry identifies 90% of bacteria directly from blood culture vials.</a> Clin Microbiol Infect. 16 (11), 1631-1638 (2010).</li><li>Novel, , 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=improved+sample+preparation+for+rapid,+direct+identification+from+positive+blood+cultures+using+matrix-assisted+laser+desorption/ionization+time-of-flight+(MALDI-TOF)+mass+spectrometry.">improved sample preparation for rapid, direct identification from positive blood cultures using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry.</a> J. Mol. Diagn. 13 (6), 701-706 (2011).</li><li>Fothergill, A., Kasinathan, V., Hyman, J., Walsh, J., Drake, T., Wang, Y. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+Identification+of+Bacteria+and+Yeasts+from+Positive-Blood-Culture+Bottles+by+Using+a+Lysis-Filtration+Method+and+Matrix-Assisted+Laser+Desorption+Ionization-Time+of+Flight+Mass+Spectrum+Analysis+with+the+SARAMIS+Database.">Rapid Identification of Bacteria and Yeasts from Positive-Blood-Culture Bottles by Using a Lysis-Filtration Method and Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrum Analysis with the SARAMIS Database.</a> J. Clin. Microbiol. 51 (3), 805-809 (2013).</li></ol>

The authors declare that they have no competing financial interests.

It is important when applying MALDI-TOF MS to blood culture broth that the post centrifugation steps are performed with sufficient care not to remix the separated components. It is particularly important to remove the blood culture constituents and human cellular proteins, including hemoglobin, which may produce spikes interfering with the MALDI-TOF spectra.
Although MS manufactures recommend cut of score of &#8805;2.0 for species and &#8805;1.7 for genus identification, other reports have sug...

Patients with bloodstream infection (BSI) due to bacteria continue to have high in-hospital mortality, ranging from 6-48%1. The delivery of appropriate empiric antibiotic promotes survival and in the subset of patients with severe sepsis, each hour delay to appropriate therapy correlates to decreased survival2,3. Accordingly, a key objective of the clinical laboratory is to rapidly detect, identify and communicate the presence of bacteria in blood cultures to inform clinical decisions. It has been demonstrated that the microbiology laboratory has the greatest influence on antimicrobial therapy at the time of reporting the Gram stain4 and recently, an observational study demonstrated that matrix-assisted laser desorption/ionization time of flight mass spectrometry&#160;(MALDI-TOF MS) performed directly on blood culture broths influence prescribing in over one third of BSI caused by Gram negative bacteria5.
The commercial development of MALDI-TOF MS has led to an efficacious laboratory tool for the identification of microorganisms6,7. The technology is now well established and has been integrated into many laboratories for rapid and accurate identification of microorganisms isolated on solid media6,8. The direct application of MALDI-TOF MS to blood culture (BC) broth that have signaled &#8220;positive&#8221; for microorganisms appeals to both clinicians and laboratory managers because of the potential to obtain an earlier identification of microorganisms at low cost.
The clinical utility of direct application of MALDI-TOF MS to blood culture broth has been limited by the wide range of sensitivities observed when compared with standard phenotypic culture based methods of identification, with reports of successful identification of Gram negative bacteria ranging from 47-98.9%9-11. The variation in sensitivity likely relates to the BC broth composition, initial bacterial concentration, variation in sample preparation methods as well as the array of Gram negative organisms encountered in study populations9. Compared with these other published protocols the method presented here avoids the use of ethanol, ammonium chloride or additional (non-matrix) acetonitrile. As a result the bacterial pellet will remain viable (until the point of protein extraction) allowing for potential phenotypic susceptibility testing methods to be applied directly to these organisms in broth. In addition, the presented method has been shown to be inexpensive, reliable and rapid with bacterial identification available within 25 min of the blood culture Gram stain results, with minimal &#8216;hands on&#8217; time12.
This method is a simple in-house spin-lysis protocol utilizing formic acid extraction applied directly to positive blood culture broths to identify Gram negative bacteria with MALDI-TOF MS technology.

<table border="0" cellpadding="0" cellspacing="0" width="1319">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:275px;">BACTEC Plus Aerobic/F Medium</td>
			<td style="width:307px;">Becton Dickinson; BD, Franklin Lakes, NJ, USA</td>
			<td align="right" style="width:188px;">442192</td>
			<td style="width:551px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BACTEC Lytic/10 Anaerobic /F Medium</td>
			<td>Becton Dickinson; BD, Franklin Lakes, NJ, USA</td>
			<td align="right">442265</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BACTEC Peds Plus Medium</td>
			<td>Becton Dickinson; BD, Franklin Lakes, NJ, USA</td>
			<td align="right">442194</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Vacutainer - Blood transfer device</td>
			<td>Becton Dickinson; BD, Franklin Lakes, NJ, USA</td>
			<td align="right">364880</td>
			<td>Single use sampling device reducing the risk of needlestick injury</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Vacutainer SST 5.0mL, Advance plus</td>
			<td>Becton Dickinson; BD, Franklin Lakes, NJ, USA</td>
			<td align="right">367954</td>
			<td>Serum separating tube</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Syringe 10 mL</td>
			<td>Becton Dickinson; BD, Franklin Lakes, NJ, USA</td>
			<td align="right">302143</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Transfer pipette</td>
			<td>Samco, USA</td>
			<td>222-20S</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Transfer pipette (fine tipped)</td>
			<td>Samco, USA</td>
			<td>232-20S</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Microcentrifuge tube (2.0 mL)</td>
			<td>Eppendorf, Hamburg, Germany</td>
			<td>0030.120.094</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sterile water (DNAse and RNAse free)</td>
			<td>Life Technologies, Carlsbad, California, USA</td>
			<td>10977-015</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Formic acid</td>
			<td>Sigma-Aldrich, St. Louis, Missouri, USA</td>
			<td>F0507</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Matrix solution&#160;</td>
			<td>Bruker Daltonics, Bremen Germany</td>
			<td align="right">285074</td>
			<td>10 mg/ml &#945;-cyano-4-hydroxycinnamic acid, 50% acetonitrile, 2.5% trifluoroacetic acid</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Benchtop microflex LT MALDI-TOF MS</td>
			<td>Bruker Daltonics, Bremen Germany</td>
			<td></td>
			<td>Utilizing BioTyper 3.1 (Build 65) and FlexControl 3.3 (Build 99) software</td>
		</tr>
	</tbody>
</table>

rapid identification of gram negative bacteria from blood culture broth using maldi-tof mass spectrometry

An important role of the clinical microbiology laboratory is to provide rapid identification of bacteria causing bloodstream infection. Traditional identification requires the sub-culture of signaled blood culture broth with identification available only after colonies on solid agar have matured. MALDI-TOF MS is a reliable, rapid method for identification of the majority of clinically relevant bacteria when applied to colonies on solid media. The application of MALDI-TOF MS directly to blood culture broth is an attractive approach as it has potential to accelerate species identification of bacteria and improve clinical management. However, an important problem to overcome is the pre-analysis removal of interfering resins, proteins and hemoglobin&#160;contained in blood culture specimens which, if not removed, interfere with the MS spectra and can result in insufficient or low discrimination identification scores. In addition it is necessary to concentrate bacteria to develop spectra of sufficient quality. The presented method describes the concentration, purification, and extraction of Gram negative bacteria allowing for the early identification of bacteria from a signaled blood culture broth.

The generated MALDI-TOF MS spectra are compared to the integrated reference database of spectra. A logarithmic score is assigned for the confidence of the match between the test isolate and the reference database isolates, with the recommendation of a score &#8805;1.7 required for probable identification to genera level (Figure 1)&#160;and &#8805;2.0 for probable identification to species (Figure 2).&#160;Report to species level when the score &#8805;1.7 and the first 5 identifications m...

Watch this Scientific Journal Video about Rapid Identification of Gram Negative Bacteria from Blood Culture Broth Using MALDI-TOF Mass Spectrometry at JoVE.com

Rapid Identification of Gram Negative Bacteria from Blood Culture Broth Using MALDI-TOF Mass Spectrometry

The application of matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) directly to blood culture broth expedites the identification of bacteria. The presented method is a rapid and reliable method for identification of Gram negative bacteria directly from blood culture broth.

An important role of the clinical microbiology laboratory is to provide rapid identification of bacteria causing bloodstream infection. Traditional ...

rapid-identification-gram-negative-bacteria-from-blood-culture-broth

Research

JoVE Journal

Immunology and Infection

24.1K Views.  Westmead Hospital. The application of matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) directly to blood culture broth expedites the identification of bacteria. The presented method is a rapid and reliable method for identification of Gram negative bacteria directly from blood culture broth.

Video: Rapid Identification of Gram Negative Bacteria from Blood Culture Broth Using MALDI-TOF Mass Spectrometry

A 1.5 Hour Procedure for Identification of Enterococcus Species Directly from Blood Cultures

Enterococci are a common cause of bacteremia with E. faecalis being the predominant species followed by E. faecium. Because resistance to ampicillin and vancomycin in E. faecalis is still uncommon compared to resistance in E. faecium, the development of rapid tests allowing differentiation between enterococcal species is important for appropriate therapy and resistance surveillance. The E. faecalis OE PNA FISH assay (AdvanDx, Woburn, MA) uses species-specific peptide nucleic acid (PNA) probes in a fluorescence in situ hybridization format and offers a time to results of 1.5 hours and the potential of providing important information for species-specific treatment. Multicenter studies were performed to assess the performance of the 1.5 hour E. faecalis/OE PNA FISH procedure compared to the original 2.5 hour assay procedure and to standard bacteriology methods for the identification of enterococci directly from a positive blood culture bottle.

A 1.5 Hour Procedure for Identification of Enterococcus Species Directly from Blood Cultures

A rapid protocol for the direct identification of Enterococcus faecalis and other Enterococcus species from a positive blood culture using a Peptide Nucleic Acid fluorescent in situ hybridization assay (PNA FISH).

Enterococci are a common cause of bacteremia with E. faecalis being the predominant species followed by E. faecium.  Because resistance to ampicillin and ...

Purification and Visualization of Lipopolysaccharide from Gram-negative Bacteria by Hot Aqueous-phenol Extraction

Lipopolysaccharide (LPS) is a major component of Gram-negative bacterial outer membranes. It is a tripartite molecule consisting of lipid A, which is embedded in the outer membrane, a core oligosaccharide and repeating O-antigen units that extend outward from the surface of the cell1, 2. LPS is an immunodominant molecule that is important for the virulence and pathogenesis of many bacterial species, including Pseudomonas aeruginosa, Salmonella species, and Escherichia coli3-5, and differences in LPS O-antigen composition form the basis for serotyping of strains. LPS is involved in attachment to host cells at the initiation of infection and provides protection from complement-mediated killing; strains that lack LPS can be attenuated for virulence6-8. For these reasons, it is important to visualize LPS, particularly from clinical isolates. Visualizing LPS banding patterns and recognition by specific antibodies can be useful tools to identify strain lineages and to characterize various mutants. 
In this report, we describe a hot aqueous-phenol method for the isolation and purification of LPS from Gram-negative bacterial cells. This protocol allows for the extraction of LPS away from nucleic acids and proteins that can interfere with visualization of LPS that occurs with shorter, less intensive extraction methods9. LPS prepared this way can be separated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) and directly stained using carbohydrate/glycoprotein stains or standard silver staining methods. Many anti-sera to LPS contain antibodies that cross-react with outer membrane proteins or other antigenic targets that can hinder reactivity observed following Western immunoblot of SDS-PAGE-separated crude cell lysates. Protease treatment of crude cell lysates alone is not always an effective way of removing this background using this or other visualization methods. Further, extensive protease treatment in an attempt to remove this background can lead to poor quality LPS that is not well resolved by any of the aforementioned methods. For these reasons, we believe that the following protocol, adapted from Westpahl and Jann10, is ideal for LPS extraction.

We describe a modified hot aqueous-phenol extraction method for purifying lipopolysaccharide (LPS) from Gram-negative bacteria. Once extracted, the LPS can be subsequently analyzed by SDS-PAGE and visualized by direct staining or Western immunoblot.

Lipopolysaccharide (LPS)  is a major component of Gram-negative bacterial outer membranes. It is a tripartite molecule consisting of  lipid A, which is ...

Detection of Bacteria Using Fluorogenic DNAzymes

Outbreaks linked to food-borne and hospital-acquired pathogens account for millions of deaths and hospitalizations as well as colossal economic losses each and every year. Prevention of such outbreaks and minimization of the impact of an ongoing epidemic place an ever-increasing demand for analytical methods that can accurately identify culprit pathogens at the earliest stage. Although there is a large array of effective methods for pathogen detection, none of them can satisfy all the following five premier requirements embodied for an ideal detection method: high specificity (detecting only the bacterium of interest), high sensitivity (capable of detecting as low as a single live bacterial cell), short time-to-results (minutes to hours), great operational simplicity (no need for lengthy sampling procedures and the use of specialized equipment), and cost effectiveness. For example, classical microbiological methods are highly specific but require a long time (days to weeks) to acquire a definitive result.1 PCR- and antibody-based techniques offer shorter waiting times (hours to days), but they require the use of expensive reagents and/or sophisticated equipment.2-4 Consequently, there is still a great demand for scientific research towards developing innovative bacterial detection methods that offer improved characteristics in one or more of the aforementioned requirements. Our laboratory is interested in examining the potential of DNAzymes as a novel class of molecular probes for biosensing applications including bacterial detection.5
DNAzymes (also known as deoxyribozymes or DNA enzymes) are man-made single-stranded DNA molecules with the capability of catalyzing chemical reactions.6-8 These molecules can be isolated from a vast random-sequence DNA pool (which contains as many as 1016 individual sequences) by a process known as "in vitro selection" or "SELEX" (systematic evolution of ligands by exponential enrichment).9-16 These special DNA molecules have been widely examined in recent years as molecular tools for biosensing applications.6-8
Our laboratory has established in vitro selection procedures for isolating RNA-cleaving fluorescent DNAzymes (RFDs; Fig. 1) and investigated the use of RFDs as analytical tools.17-29 RFDs catalyze the cleavage of a DNA-RNA chimeric substrate at a single ribonucleotide junction (R) that is flanked by a fluorophore (F) and a quencher (Q). The close proximity of F and Q renders the uncleaved substrate minimal fluorescence. However, the cleavage event leads to the separation of F and Q, which is accompanied by significant increase of fluorescence intensity.
More recently, we developed a method of isolating RFDs for bacterial detection.5 These special RFDs were isolated to "light up" in the presence of the crude extracellular mixture (CEM) left behind by a specific type of bacteria in their environment or in the media they are cultured (Fig. 1). The use of crude mixture circumvents the tedious process of purifying and identifying a suitable target from the microbe of interest for biosensor development (which could take months or years to complete). The use of extracellular targets means the assaying procedure is simple because there is no need for steps to obtain intracellular targets.
Using the above approach, we derived an RFD that cleaves its substrate (FS1; Fig. 2A) only in the presence of the CEM produced by E. coli (CEM-EC).5 This E. coli-sensing RFD, named RFD-EC1 (Fig. 2A), was found to be strictly responsive to CEM-EC but nonresponsive to CEMs from a host of other bacteria (Fig. 3).
Here we present the key experimental procedures for setting up E. coli detection assays using RFD-EC1 and representative results.

We have recently reported a novel approach for generating fluorogenic DNAzyme probes that can be applied to set up a simple, "mix-and-read" fluorescent assay for bacterial detection. These special DNA probes catalyze the cleavage of a chromophore-modified DNA-RNA chimeric substrate in the presence of crude extracellular mixture (CEM) produced by a specific bacterium, thereby translating bacterial detection into fluorescence signal generation. In this report we will describe key experimental procedures where a specific DNAzyme probe denoted "RFD-EC1" is employed for the detection of the model bacterium, Escherichia coli (E. coli).

Outbreaks linked to food-borne and hospital-acquired pathogens account for millions of deaths and hospitalizations as well as colossal economic losses ...

Whole-cell MALDI-TOF Mass Spectrometry is an Accurate and Rapid Method to Analyze Different Modes of Macrophage Activation

MALDI-TOF is an extensively used mass spectrometry technique in chemistry and biochemistry. It has been also applied in medicine to identify molecules and biomarkers. Recently, it has been used in microbiology for the routine identification of bacteria grown from clinical samples, without preparation or fractionation steps. We and others have applied this whole-cell MALDI-TOF mass spectrometry technique successfully to eukaryotic cells. Current applications range from cell type identification to quality control assessment of cell culture and diagnostic applications. Here, we describe its use to explore the various polarization phenotypes of macrophages in response to cytokines or heat-killed bacteria. It allowed the identification of macrophage-specific fingerprints that are representative of the diversity of proteomic responses of macrophages. This application illustrates the accuracy and simplicity of the method. The protocol we described here may be useful for studying the immune host response in pathological conditions or may be extended to wider diagnostic applications.

This protocol describes the use of whole-cell MALDI-TOF mass spectrometry on eukaryotic cells. Here, we illustrate the accuracy of this technique by analyzing the multiple activation states of macrophages in response to their microenvironment.

MALDI-TOF is an extensively used mass spectrometry technique in chemistry and biochemistry. It has been also applied in medicine to identify molecules and ...

Isolation of Double Negative &#945;&#946; T Cells from the Kidney

There is currently no standard protocol for the isolation of DN T cells from the non-lymphoid tissues despite their increasingly reported involvement in various immune responses. DN T cells are a unique immune cell type that has been implicated in regulating immune and autoimmune responses and tolerance to allotransplants1-6. DN T cells are, however, rare in peripheral blood and secondary lymphoid organs (spleen and lymph nodes), but are major residents of the normal kidney. Very little is known about their pathophysiologic function7 due to their paucity in the periphery. We recently described a comprehensive phenotypic and functional analysis of this population in the kidney8 in steady state and during ischemia reperfusion injury. Analysis of DN T cell function will be greatly enhanced by developing a protocol for their isolation from the kidney.
Here, we describe a novel protocol that allows isolation of highly pure ab CD4+ CD8+ T cells and DN T cells from the murine kidney. Briefly, we digest kidney tissue using collagenase and isolate kidney mononuclear cells (KMNC) by density gradient. This is followed by two steps to enrich hematopoietic T cells from 3% to 70% from KMNC. The first step consists of a positive selection of hematopoietic cells using a CD45+ isolation kit. In the second step, DN T cells are negatively isolated by removal of non-desired cells using CD4, CD8, and MHC class II monoclonal antibodies and CD1d &#945;-galcer tetramer. This strategy leads to a population of more than 90% pure DN T cells. Surface staining with the above mentioned antibodies followed by FACs analysis is used to confirm purity.

Isolation of Double Negative &amp;#945;&amp;#946; T Cells from the Kidney

DNabT cells are rare among peripheral T cells; however, they are abundant in certain non-lymphoid tissues. Difficulty of isolating DN T cells from non-lymphoid tissue hinders their functional analysis despite increasing recognized pathophysiologic significance. We describe a novel protocol for isolation of highly purified DN T cells from murine kidney.

There is currently no standard protocol for the isolation of DN T cells from the non-lymphoid tissues despite their increasingly reported involvement in ...

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 ...

A Reference Broth Microdilution Method for Dalbavancin In Vitro Susceptibility Testing of Bacteria that Grow Aerobically

Antimicrobial susceptibility testing (AST) is performed to assess the in vitro activity of antimicrobial agents against various bacteria. The AST results, which are expressed as minimum inhibitory concentrations (MICs) are used in research for antimicrobial development and monitoring of resistance development and in the clinical setting for antimicrobial therapy guidance. Dalbavancin is a semi-synthetic lipoglycopeptide antimicrobial agent that was approved in May 2014 by the Food and Drug Administration (FDA) for the treatment of acute bacterial skin and skin structure infections caused by Gram-positive organisms. The advantage of dalbavancin over current anti-staphylococcal therapies is its long half-life, which allows for once-weekly dosing. Dalbavancin has activity against Staphylococcus aureus (including both methicillin-susceptible S. aureus [MSSA] and methicillin-resistant S. aureus [MRSA]), coagulase-negative staphylococci, Streptococcus pneumoniae, Streptococcus anginosus group, &#946;-hemolytic streptococci and vancomycin susceptible enterococci. Similar to other recent lipoglycopeptide agents, optimization of CLSI and ISO broth susceptibility test methods includes the use of dimethyl sulfoxide (DMSO) as a solvent when preparing stock solutions and polysorbate 80 (P80) to alleviate adherence of the agent to plastic. Prior to the clinical studies and during the initial development of dalbavancin, susceptibility studies were not performed with the use of P-80 and MIC results tended to be 2-4 fold higher and similarly higher MIC results were obtained with the agar dilution susceptibility method. Dalbavancin was first included in CLSI broth microdilution methodology tables in 2005 and amended in 2006 to clarify use of DMSO and P-80. The broth microdilution (BMD) procedure shown here is specific to dalbavancin and is in accordance with the CLSI and ISO methods, with step-by-step detail and focus on the critical steps added for clarity.

A Reference Broth Microdilution Method for Dalbavancin In Vitro Susceptibility Testing of Bacteria that Grow Aerobically

Here, we present a protocol for determination of dalbavancin susceptibility of clinically relevant Gram-positive bacteria using a broth microdilution reference methodology.

Antimicrobial susceptibility testing (AST) is performed to assess the in vitro activity of antimicrobial agents against various bacteria. The AST results, ...

Identification of Rare Bacterial Pathogens by 16S rRNA Gene Sequencing and MALDI-TOF MS

There are a number of rare and, therefore, insufficiently described bacterial pathogens which are reported to cause severe infections especially in immunocompromised patients. In most cases only few data, mostly published as case reports, are available which investigate the role of such pathogens as an infectious agent. Therefore, in order to clarify the pathogenic character of such microorganisms, it is necessary to conduct epidemiologic studies which include large numbers of these bacteria. The methods used in such a surveillance study have to meet the following criteria: the identification of the strains has to be accurate according to the valid nomenclature, they should be easy to handle (robustness), economical in routine diagnostics and they have to generate comparable results among different laboratories. Generally, there are three strategies for identifying bacterial strains in a routine setting: 1) phenotypic identification characterizing the biochemical and metabolic properties of the bacteria, 2) molecular techniques such as 16S rRNA gene sequencing and 3) mass spectrometry as a novel proteome based approach. Since mass spectrometry and molecular approaches are the most promising tools for identifying a large variety of bacterial species, these two methods are described. Advances, limitations and potential problems when using these techniques are discussed.

Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) and molecular techniques (16S rRNA gene sequencing) permit the identification of rare bacterial pathogens in routine diagnostics. The goal of this protocol lies in the combination of both techniques which leads to more accurate and reliable data.

There are a number of rare and, therefore, insufficiently described bacterial pathogens which are reported to cause severe infections especially in ...

Culture of Macrophage Colony-stimulating Factor Differentiated Human Monocyte-derived Macrophages

A protocol is presented for cell culture of macrophage colony-stimulating factor (M-CSF) differentiated human monocyte-derived macrophages. For initiation of experiments, fresh or frozen monocytes are cultured in flasks for 1 week with M-CSF to induce their differentiation into macrophages. Then, the macrophages can be harvested and seeded into culture wells at required cell densities for carrying out experiments. The use of defined numbers of macrophages rather than defined numbers of monocytes to initiate macrophage cultures for experiments yields macrophage cultures in which the desired cell density can be more consistently attained. Use of cryopreserved monocytes reduces dependency on donor availability and produces more homogeneous macrophage cultures.

A protocol is presented for cell culture of macrophage colony-stimulating factor (M-CSF) differentiated human monocyte-derived macrophages. The protocol utilizes cryopreservation of monocytes coupled with their bulk differentiation into macrophages. Then harvested macrophages can then be seeded into culture wells at required cell densities for carrying out experiments.

A protocol is presented for cell culture of macrophage colony-stimulating factor (M-CSF) differentiated human monocyte-derived macrophages. For initiation ...

Dextran Enhances the Lentiviral Transduction Efficiency of Murine and Human Primary NK Cells

The efficient transduction of specific genes into natural killer (NK) cells has been a major challenge. Successful transductions are critical to defining the role of the gene of interest in the development, differentiation, and function of NK cells. Recent advances related to chimeric antigen receptors (CARs) in cancer immunotherapy accentuate the need for an efficient method to deliver exogenous genes to effector lymphocytes. The efficiencies of lentiviral-mediated gene transductions into primary human or mouse NK cells remain significantly low, which is a major limiting factor. Recent advances using cationic polymers, such as polybrene, show an improved gene transduction efficiency in T cells. However, these products failed to improve the transduction efficiencies of NK cells. This work shows that dextran, a branched glucan polysaccharide, significantly improves the transduction efficiency of human and mouse primary NK cells. This highly reproducible transduction methodology provides a competent tool for transducing human primary NK cells, which can vastly improve clinical gene delivery applications and thus NK cell-based cancer immunotherapy.

The goal of this study was to formulate technologies that allow for successful gene transduction in primary natural killer (NK) cells. The dextran-mediated lentiviral transduction of human or mouse primary NK cells results in higher gene expression efficiencies. This method of gene transduction will vastly improve NK cell genetic manipulation.

The efficient transduction of specific genes into natural killer (NK) cells has been a major challenge. Successful transductions are critical to defining ...