Name: a high-throughput, high-content, liquid-based c. elegans pathosystem
Uploaded: 2018-07-01T15:00:00
Description: Watch this Scientific Journal Video about A High-throughput, High-content, Liquid-based C. elegans Pathosystem at JoVE.com

This study was supported by the Cancer Prevention and Research Institute of Texas (CPRIT) Award RR150044, Welch Foundation Research Grant C-1930, and by the National Institutes of Health K22 AI110552 awarded to NVK. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Caution: P. aeruginosa and E. faecalis are Biosafety Level 2 pathogens, and proper safety precautions must be taken to prevent accidental infection and to minimize contamination of surfaces. All media and materials that come into contact with pathogens must be sterilized and/or discarded. Further guidelines are available from the CDC publication Biosafety in Microbiological and Biomedical Laboratories (BMBL), 5th edition.
1. Preparation and Maintenance of P. aeruginosa...

<ol>
	<li>Falagas, M. 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=Pandrug-resistant+Klebsiella+pneumoniae,+Pseudomonas+aeruginosa+and+Acinetobacter+baumannii+infections:+Characteristics+and+outcome+in+a+series+of+28+patients.">Pandrug-resistant Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii infections: Characteristics and outcome in a series of 28 patients.</a> International Journal of Antimicrobial Agents. 32 (5), 450-454 (2008).</li><li>Hsueh, P. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pandrug-resistant+Acinetobacter+baumannii+causing+nosocomial+infections+in+a+university+hospital,+Taiwan.">Pandrug-resistant Acinetobacter baumannii causing nosocomial infections in a university hospital, Taiwan.</a> Emerging Infectious Diseases. 8 (8), 827-832 (2002).</li><li>Wang, C. Y., 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=Pandrug-resistant+Pseudomonas+aeruginosa+among+hospitalised+patients:+clinical+features,+risk-factors+and+outcomes.">Pandrug-resistant Pseudomonas aeruginosa among hospitalised patients: clinical features, risk-factors and outcomes.</a> Clinical Microbiology and Infection. 12 (1), 63-68 (2006).</li><li>Yao, Y., 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=Draft+genome+sequences+of+pandrug-resistant+Serratia+marcescens+clinical+isolates+harboring+blaNDM-1.">Draft genome sequences of pandrug-resistant Serratia marcescens clinical isolates harboring blaNDM-1.</a> Genome Announcements. 5 (3), (2017).</li><li>Utari, P. D., Quax, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caenorhabditis+elegans+reveals+novel+Pseudomonas+aeruginosa+virulence+mechanism.">Caenorhabditis elegans reveals novel Pseudomonas aeruginosa virulence mechanism.</a> Trends in Microbiology. 21 (7), 315-316 (2013).</li><li>Conery, A. L., Larkins-Ford, J., Ausubel, F. M., Kirienko, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-throughput+screening+for+novel+anti-infectives+using+a+C.+elegans+pathogenesis+model.">High-throughput screening for novel anti-infectives using a C. elegans pathogenesis model.</a> Current Protocols in Chemical Biology. 6 (1), 25-37 (2014).</li><li>Kirienko, N. V., 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=Pseudomonas+aeruginosa+disrupts+Caenorhabditis+elegans+iron+homeostasis,+causing+a+hypoxic+response+and+death.">Pseudomonas aeruginosa disrupts Caenorhabditis elegans iron homeostasis, causing a hypoxic response and death.</a> Cell Host &amp; Microbe. 13 (4), 406-416 (2013).</li><li>Kirienko, D. R., Revtovich, A. V., Kirienko, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+high-content,+phenotypic+screen+identifies+fluorouridine+as+an+inhibitor+of+pyoverdine+biosynthesis+and+pseudomonas+aeruginosa+virulence.">A high-content, phenotypic screen identifies fluorouridine as an inhibitor of pyoverdine biosynthesis and pseudomonas aeruginosa virulence.</a> mSphere. 1 (4), (2016).</li><li>Manning, A. J., 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+high+content+microscopy+assay+to+determine+drug+activity+against+intracellular+Mycobacterium+tuberculosis.">A high content microscopy assay to determine drug activity against intracellular Mycobacterium tuberculosis.</a> Methods. 127, 3-11 (2017).</li><li>Marwaha, 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=N-acylated+derivatives+of+sulfamethoxazole+and+sulfafurazole+inhibit+intracellular+growth+of+Chlamydia+trachomatis.">N-acylated derivatives of sulfamethoxazole and sulfafurazole inhibit intracellular growth of Chlamydia trachomatis.</a> Antimicrobial Agents and Chemotherapy. 58 (5), 2968-2971 (2014).</li><li>Kota, K. 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=Integrating+high-content+imaging+and+chemical+genetics+to+probe+host+cellular+pathways+critical+for+Yersinia+pestis+infection.">Integrating high-content imaging and chemical genetics to probe host cellular pathways critical for Yersinia pestis infection.</a> PLoS One. 8 (1), e55167 (2013).</li><li>Arif, 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=Quantification+of+cell+infection+caused+by+Listeria+monocytogenes+invasion.">Quantification of cell infection caused by Listeria monocytogenes invasion.</a> Journal of Biotechnology. 154 (1), 76-83 (2011).</li><li>Jayamani, 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=Characterization+of+a+Francisella+tularensis-Caenorhabditis+elegans+pathosystem+for+the+evaluation+of+therapeutic+compounds.">Characterization of a Francisella tularensis-Caenorhabditis elegans pathosystem for the evaluation of therapeutic compounds.</a> Antimicrobial Agents and Chemotherapy. 61 (9), (2017).</li><li>Moy, T. I., 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=High-throughput+screen+for+novel+antimicrobials+using+a+whole+animal+infection+model.">High-throughput screen for novel antimicrobials using a whole animal infection model.</a> ACS Chemical Biology. 4 (7), 527-533 (2009).</li><li>Rajamuthiah, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole+animal+automated+platform+for+drug+discovery+against+multi-drug+resistant+Staphylococcus+aureus.">Whole animal automated platform for drug discovery against multi-drug resistant Staphylococcus aureus.</a> PLoS One. 9 (2), e89189 (2014).</li><li>Breger, J., 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=Antifungal+chemical+compounds+identified+using+a+C.+elegans+pathogenicity+assay.">Antifungal chemical compounds identified using a C. elegans pathogenicity assay.</a> PLoS Pathogens. 3 (2), e18 (2007).</li><li>Garvis, 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=Caenorhabditis+elegans+semi-automated+liquid+screen+reveals+a+specialized+role+for+the+chemotaxis+gene+cheB2+in+Pseudomonas+aeruginosa+virulence.">Caenorhabditis elegans semi-automated liquid screen reveals a specialized role for the chemotaxis gene cheB2 in Pseudomonas aeruginosa virulence.</a> PLoS Pathogens. 5 (8), e1000540 (2009).</li><li>Zhou, Y. 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=An+efficient+and+novel+screening+model+for+assessing+the+bioactivity+of+extracts+against+multidrug-resistant+Pseudomonas+aeruginosa+using+Caenorhabditis+elegans.">An efficient and novel screening model for assessing the bioactivity of extracts against multidrug-resistant Pseudomonas aeruginosa using Caenorhabditis elegans.</a> Bioscience, Biotechnology, and Biochemistry. 75 (9), 1746-1751 (2011).</li><li>Leung, C. K., Deonarine, A., Strange, K., Choe, K. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-throughput+screening+and+biosensing+with+fluorescent+C.+elegans+strains.">High-throughput screening and biosensing with fluorescent C. elegans strains.</a> Journal of Visual Experiments. (51), (2011).</li><li>Kirienko, N. V., Ausubel, F. M., Ruvkun, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitophagy+confers+resistance+to+siderophore-mediated+killing+by+Pseudomonas+aeruginosa.">Mitophagy confers resistance to siderophore-mediated killing by Pseudomonas aeruginosa.</a> Proceedings of the National Academy of Sciences of the United States of America. 112 (6), 1821-1826 (2015).</li><li>Kirienko, N. V., Cezairliyan, B. O., Ausubel, F. M., Powell, 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=Pseudomonas+aeruginosa+PA14+pathogenesis+in+Caenorhabditis+elegans.">Pseudomonas aeruginosa PA14 pathogenesis in Caenorhabditis elegans.</a> Methods in Molecular Biology. 1149, 653-669 (2014).</li><li>Kang, D., Kirienko, D. R., Webster, P., Fisher, A. L., Kirienko, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pyoverdine,+a+siderophore+from+Pseudomonas+aeruginosa,+translocates+into+C.+elegans,+removes+iron,+and+activates+a+distinct+host+response.">Pyoverdine, a siderophore from Pseudomonas aeruginosa, translocates into C. elegans, removes iron, and activates a distinct host response.</a> Virulence. , 1-41 (2018).</li><li>Garsin, D. 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=Long-lived+C.+elegans+daf-2+mutants+are+resistant+to+bacterial+pathogens.">Long-lived C. elegans daf-2 mutants are resistant to bacterial pathogens.</a> Science. 300 (5627), 1921 (2003).</li><li>Estes, K. A., Dunbar, T. L., Powell, J. R., Ausubel, F. M., Troemel, E. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=bZIP+transcription+factor+zip-2+mediates+an+early+response+to+Pseudomonas+aeruginosa+infection+in+Caenorhabditis+elegans.">bZIP transcription factor zip-2 mediates an early response to Pseudomonas aeruginosa infection in Caenorhabditis elegans.</a> Proceedings of the National Academy of Sciences of the United States of America. 107 (5), 2153-2158 (2010).</li><li>Tjahjono, E., Kirienko, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+conserved+mitochondrial+surveillance+pathway+is+required+for+defense+against+Pseudomonas+aeruginosa.">A conserved mitochondrial surveillance pathway is required for defense against Pseudomonas aeruginosa.</a> PLoS Genetics. 13 (6), e1006876 (2017).</li><li>Moy, T. I., 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=Identification+of+novel+antimicrobials+using+a+live-animal+infection+model.">Identification of novel antimicrobials using a live-animal infection model.</a> Proceedings of the National Academy of Sciences of the United States of America. 103 (27), 10414-10419 (2006).</li><li>Henderson, S. T., Bonafe, M., Johnson, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=daf-16+protects+the+nematode+Caenorhabditis+elegans+during+food+deprivation.">daf-16 protects the nematode Caenorhabditis elegans during food deprivation.</a> The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. 61 (5), 444-460 (2006).</li><li>Beanan, M. J., Strome, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+a+germ-line+proliferation+mutation+in+C.+elegans.">Characterization of a germ-line proliferation mutation in C. elegans.</a> Development. 116 (3), 755-766 (1992).</li></ol>

This assay (or similar assays where other pathogens are substituted for P. aeruginosa or E. faecalis) is useful for a variety of purposes, including drug discovery. It is also useful for addressing fundamental biological questions, such as identifying virulence factors, the elucidation of host defense pathways, and determining the regulatory machinery involved in the host-pathogen interaction.
Although the P. aeruginosa Liquid Killing assay is robust, there are sever...

The identification and development of effective, broad-spectrum antibiotics, now almost a century ago, led to a watershed moment in public health where there was a wide-spread belief that infectious disease would be a scourge of the past. Within a few short decades, this optimism began to wane, as pathogen after pathogen developed resistance mechanisms that limited these once miraculous treatments. For some time, the arms race between drug discovery efforts and the pathogens seemed balanced. However, the misuse of antimicrobials has recently culminated in the emergence of pan-drug resistant strains of Klebsiella pneumoniae, Acinetobacter baumanii, Serratia marcescens, and P. aeruginosa1,2,3,4.
P. aeruginosa is an opportunistic, gram negative, multi-host pathogen that is a severe threat to patients with severe burns, those who are immunocompromised, or have cystic fibrosis. It is also increasingly identified as a causative agent in severe nosocomial infections, particularly due to its ongoing acquisition of antimicrobial resistance. To begin to address this threat, we have used the well-documented C. elegans-P. aeruginosa infection system5. Our lab has leveraged this system to develop a liquid-based, high-throughput, high-content screening platform to identify novel compounds that limit the ability of the pathogen to kill the host6. Intriguingly, these compounds seem to belong to at least three general categories, including antimicrobials7 and virulence inhibitors8. Other high-content drug discovery assays in C. elegans have been reported for Mycobacterium tuberculosum, Chlamydia trachomatis, Yersinia pestis, Listeria monocytogenes, Francisella tularensis, Staphylococcus aureus, Candida albicans, and Enterococcus faecalis, among others9,10,11,12,13,14,15,16. These types of assays have several well-recognized advantages, such as limiting false positive hits that may be toxic to both the host and the pathogen, increased likelihood of bioavailability compared to a chemical screen, and the ability to identify hits beyond simply limiting microbial growth, such as anti-virulents, immune stimulatory molecules, or compounds that otherwise tilt the balance of the host-pathogen interaction in favor of the former. Additionally, the compounds discovered in these screens are often effective in mammalian hosts.
It is worth noting that at least two other assays17,18 are available to carry out high-throughput screens in C. elegans in liquid. However, each of these assays is a modification that allows the prototypical intestinal-colonization assay, known as slow-killing, to be performed in liquid, increasing throughput and allowing compounds to be more readily screened. Careful characterization has conclusively demonstrated that the mechanisms of bacterial virulence are different between these assays and our liquid-based screen7. Since both types of virulence are observed in mammalian systems, it is important to consider which virulence determinant is most relevant for the experimenter&#39;s interests prior to assay selection.
Here we demonstrate an optimized version of the liquid-based C. elegans-P. aeruginosa assay. We also report the adaptation of our liquid-based assay method to accommodate the gram-positive bacterial pathogen Enterococcus faecalis. Like P. aeruginosa, E. faecalis is increasingly identified as a serious nosocomial threat with a growing armament of antimicrobial resistance pathways1. Although a previous method for high-throughput screening of E. faecalis exists14, it requires preinfection with the pathogen, which complicates the procedure and increases the likelihood of contaminating equipment like the COPAS FlowSort. Our protocol eliminates the need for pre-infection, improving the safety profile. Finally, we report a means by which either of these assays can be combined with feeding RNAi, allowing the user to search for host factors that play a role in the establishment of, or resistance to, infection.

<table>
	<tbody>
		<tr>
			<td>COPAS FP BioSorter</td>
			<td>Union Biometrica</td>
			<td></td>
			<td>Large object flow cytometer/worm sorter</td>
		</tr>
		<tr>
			<td>Cytation 5</td>
			<td>BioTek</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EL406 Washer Dispenser</td>
			<td>BioTek</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Multitron Pro</td>
			<td>Infors HT</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>24 Deep-Well RB Block</td>
			<td>Thermo Fisher Scientific</td>
			<td>CS15124</td>
			<td></td>
		</tr>
		<tr>
			<td>384-Well plate</td>
			<td>Greiner Bio-One</td>
			<td>MPG-781091</td>
			<td></td>
		</tr>
		<tr>
			<td>Nematode Growth Media (NGM)</td>
			<td></td>
			<td></td>
			<td>Amount per liter: 18 grams agar, 3 grams NaCl, 2.5 grams Peptone, 1 mL CaCl2 (1 M), 1 mL MgSO4 (1 M), 25 mL Phospate buffer, and 973 mL of milli-Q water</td>
		</tr>
		<tr>
			<td>Slow Killing (SK) plates</td>
			<td></td>
			<td></td>
			<td>Amount per liter: 18 grams agar, 3 grams NaCl, 3.5 grams Peptone, 1 mL CaCl2 (1 M), 1 mL MgSO4 (1 M), 25 mL Phospate buffer, and 973 mL of milli-Q water</td>
		</tr>
		<tr>
			<td>Slow Killing (SK) media</td>
			<td></td>
			<td></td>
			<td>Amount per liter:&#160; 3 grams NaCl, 3.5 grams Peptone, 1 mL CaCl2 (1 M), 1 mL MgSO4 (1 M), 25 mL Phosphate buffer, and 973 mL of milli-Q water</td>
		</tr>
		<tr>
			<td>Lysogeny Broth (LB)</td>
			<td>USBiological Life Sciences</td>
			<td>L1520</td>
			<td></td>
		</tr>
		<tr>
			<td>Brian Heart Infusion broth (BHI)</td>
			<td>Research Products International Corp</td>
			<td>50-488-526</td>
			<td></td>
		</tr>
		<tr>
			<td>Worm Bleach Solution</td>
			<td></td>
			<td></td>
			<td>Amount per 100 mL: 10 mL of 5 M NaOH solution, 20 mL of 5% Sodium Hypochlorite Solution, and 70 mL of sterile water</td>
		</tr>
		<tr>
			<td>S Basal</td>
			<td></td>
			<td></td>
			<td>Amount per liter: 5.85 grams NaCl, 6 grams KH2PO4, 1 gram K2HPO4, and 1 Liter of milli-Q water</td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>USBiological Life Sciences</td>
			<td>A0930</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>USBiological Life Sciences</td>
			<td>S5000</td>
			<td></td>
		</tr>
		<tr>
			<td>Peptone</td>
			<td>USBiological Life Sciences</td>
			<td>P3300</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>USBiological Life Sciences</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Fisher Scientific</td>
			<td>M63-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Phospate buffer</td>
			<td></td>
			<td></td>
			<td>amount per liter: 132 mL of K2HPO4 (1M) and 868 mL of KH2PO4 (1M)</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Acros Organics</td>
			<td>7778-77-0</td>
			<td></td>
		</tr>
		<tr>
			<td>K2HPO4</td>
			<td>USBiological Life Sciences</td>
			<td>P5100</td>
			<td></td>
		</tr>
		<tr>
			<td>5% Sodium Hypochlorite Solution</td>
			<td>BICCA</td>
			<td>7495.5-32</td>
			<td></td>
		</tr>
		<tr>
			<td>NaOH solution</td>
			<td>Fisher Scientific</td>
			<td>SS255-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Breathe-easy</td>
			<td>Diversified Biotech</td>
			<td>BEM-1</td>
			<td></td>
		</tr>
		<tr>
			<td>SYTOX Orange Nucleic Acid Stain</td>
			<td>Fisher Scientific</td>
			<td>S11368</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacterial Strains</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>P. aeruginosa (PA14)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>E. faecalis(OG1RF)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>E. coli superfood (OP50)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>E. coli RNAi expressing bacteria (HT115)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Worm Strains </td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>glp-4(bn2) (Beanan and Strome, 1992, PMID: 1289064)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PINK-1::GFP reporter (Kang et al., 2018, PMID: 29532717)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

a high-throughput, high-content, liquid-based c. elegans pathosystem

The number of new drugs identified by traditional, in vitro screens has waned, reducing the success of this approach in the search for new weapons to combat multiple drug resistance. This has led to the conclusion that researchers do not only need to find new drugs, but also need to develop new ways of finding them. Amongst the most promising candidate methods are whole-organism, in vivo assays that use high-throughput, phenotypic readouts and hosts that range from Caenorhabditis elegans to Danio rerio. These hosts have several powerful advantages, including dramatic reductions in false positive hits, as compounds that are toxic to the host and/or biounavailable are typically dropped in the initial screen, prior to costly follow up.
Here we show how our assay has been used to interrogate host variation in the well-documented C. elegans&#8212;Pseudomonas aeruginosa liquid killing pathosystem. We also demonstrate several extensions of this well-worked out technique. For example, we are able to carry out high-throughput genetic screens using RNAi in 24- or 96-well plate formats to query host factors in this host-pathogen interaction. Using this assay, whole genome screens can be completed in only a few months, which can dramatically simplify the task of identifying drug targets, potentially without the need for laborious biochemical purification approaches.
We also report here a variation of our method that substitutes the gram-positive bacterium Enterococcus faecalis for the gram-negative pathogen P. aeruginosa. Much as is the case for P. aeruginosa, killing by E. faecalis is time-dependent. Unlike previous C. elegans&#8212;E. faecalis assays, our assay for E. faecalis does not require preinfection, improving its safety profile and reducing the chances of contaminating liquid-handling equipment. The assay is highly robust, showing ~95% death rates 96 h post infection.

Important parameters for assay performance
A proper understanding of the biology underlying this assay is necessary for troubleshooting and optimizing the assay. To that end, we refer first to several key papers elucidating the mechanisms of pathogenesis of P. aeruginosa-mediated killing in liquid7,20. Provided that the steps outlined above are followed...

Watch this Scientific Journal Video about A High-throughput, High-content, Liquid-based C. elegans Pathosystem at JoVE.com

A High-throughput, High-content, Liquid-based C. elegans Pathosystem

Here we describe a protocol that is an adaptable, whole host, high-content screening tool that can be utilized to study host-pathogen interactions and be used for drug discovery.

A High-throughput, High-content, Liquid-based C. elegans Pathosystem

The number of new drugs identified by traditional, in vitro screens has waned, reducing the success of this approach in the search for new weapons to ...

This method can answer questions in host pathogen interaction and drug discovery, such as the the importance of various virulence factors and the ability of small molecules to ameliorate with the genesis. The main advantage of this technique is that it takes place in a liquid format with small volumes. To begin, while working inside a BSL 2 biosafety cabinet, streak P.aeruginosa from a frozen stock onto an LB Agar plate.Incubate the plate at 37 degrees C for 16 to 24 hours, then store the plate at four degrees Celsius for up to one week. Two days prior to setting up assay plates, use a single colony from the plate to inoculate three to five milliliters of sterile LB broth. Incubate the culture at 37 degrees Celsius for 12 to 16 hours.After preparing the slow kill or SK media according to the text protocol, with 350 milliliters of p. Aeruginosa from the fresh overnight LB culture, seed each 10 centimeter SK plate. Use a sterile bacterial spreader to evenly spread the bacteria, and allow the plates to dry in the biosafety cabinet.Then, incubate the plates at 37 degrees Celsius for 24 hours. To test multiple RNAi bacterial strains in parallel in a single well of a 24 well deep well plate, inoculate a single colony from each clone of previously prepared RNAi containing bacteria into four milliliters of carbenicillin supplemented LB.Place the plates into a shaking incubator optimized for multi-well plates at 37 degrees Celsius and 950 rpm for 16 hours, then collect the bacteria by centrifugation at 2, 000 g for 5 minutes. Decant the supernatant by inverting the plate and vigorously shaking it.Using 100 microliters of S Basal resuspend the RNAi bacteria. Pipette the resuspended bacteria into an appropriate number of wells of a multi-well NGM plate supplemented with IPTG and carbenicillin and allow the plate to dry. After preparing L1 worms according to the text protocol, prepare plates for basic experiments by pipetting approximately 5, 000 worms per 10 centimeter plate, seeded with RNAi or OP50 superfood.To set up for an RNAi screen, pipette approximately 300 worms per well in a 24 well plate seeded with RNAi. If the strain being used is temperature-sterile, incubate the worms at 15 degrees Celsius for approximately 16 hours and then transfer them to 25 degrees Celsius for 44 hours to complete development and prevent embryogenesis. To carry out a liquid killing assay use a cell scraper to remove the P.aeruginosa from an SK plateand resuspend the bacteria in approximately 5 milliliters of S.Basal.Using a spectrophotometer meaure the OD 600 of the bacterial suspension. Prepare 24 milliliters of diluted stock of P.Aeruginosa in S.Basal at an OD 600 equal to 09, then add 21 milliliters of liquid SK media, and, using a multichannel pipette, transfer 45 microliters of bacteria and media to each well of a 384 well plate. Wash the worms from their source into a 50 milliliter conical tube, and allow them to settle under gravitational force.Aspirate the supernatant to 5 milliliters, then use a total of 50 milliliters of S.Basal to resuspend the worms, and repeat the wash twice more. Using a worm sorter, sort approximately 22 worms into each well of a 384 well plate, according to the text protocol, then use a gas-permeable film to seal the plate and incubate it at 25 degrees Celsius for 24 to 48 hours. At the desired time, use a microplate washer and S.Basal to wash the 384 well plate a total of 5 times.One of the easiest mistakes to make is to aspirate the 384 well plate before worms have completely settled. It takes practice to accurately see whether the worms have settled completely. After the final wash, aspirate the supernatant down to 20 microliters.Then, add 50 microliters of 98 micromolar nucleic acid stain per well, for a final concentration of 0.7 micromolar. Incubate the plate at room temperature for 12 to 16 hours. After the desired incubation period, use the microplate washer to wash the plates a minimum of three times.For a data acquisition use a spectrophotometer or an automated microscope to image both transmitted light and fluorescence. Add one milliliter of S Basal per well of a 24 well plate containing 300 worms per well. Gently agitate the worms by shaking the plate, then transfer worms to an empty, sterile 24 deep well plate.Allow the worms to settle gravitationally, about five minutes. Aspirate the supernatant, leaving approximately one milliliter per well, Then add 7 milliliters of S Basal to each well. Repeat the wash two more times, and then after the final wash aspirate all but approximately 400 microliters of supernatant.After pipetting the bacteria into 384 well plates to avoid starvation, using the resampler function of the worm sorter sort 22 worms into each well of a 384 well plate. Finally, following sorting, add small molecules or other experiment specific materials. As illustrated in this graph, when the steps outlined in this video are followed, a time dependent killing of C.elegans will be observed only in the presence of P.aeruginosa.In contrast, in the absence of key bacterial nutritional supplements, little to no killing will be observed. As shown here, the two step incubation of P.aeruginosa at 37 degrees Celsius and then 25 degrees Celsius, which is critical for conventional slow killing assays, and was originally implemented in liquid killing, is dispensable in this assay. The protocol tolerates a wide range of initial bacterial concentrations, from as low as an OD 600 equal to 0025, and still exhibits time and concentration dependent killing, although the timing does shift.In addition, as few as four wells is frequently sufficient to obtain statistically significant data. An example of the utility of processing is shown here when the signal-to-noise ratio is high, as in this example, analysis is simple and discriminating between positive and negative conditions is trivial. In these cases, even weak hits can be readily identified.Once mastered, this technique can be performed in about 60 to 75 minutes of hands on time per 384 well plate, not including sorting. While attempting this procedure, it's critical to remember to add all the components to your media or virulence will be compromised. This assay simplifies the application of whole organism phenotype based screening to drug discovery in host-pathogen research.After watching this video, you should have a good understanding of how to carry out liquid-based C elegans pathogenesis assays. This procedure can be modified by substituting with other pathogens, such as E.Faecalis for P.Aeruginosa, facilitating the search for treatments for other bacterial infections. Don't forget that working with infectious bacteria like P.Aeruginosa or E.Faecalis can be dangerous.Appropriate precautions, such as proper training, good personal protective equipment, and proper technique, should always be taken while performing this procedure.

a-high-throughput-high-content-liquid-based-c-elegans-pathosystem

Research

JoVE Journal

Immunology and Infection

Automated Separation of C. elegans Variably Colonized by a Bacterial Pathogen

The wormsorter is an instrument analogous to a FACS machine that is used in studies of Caenorhabditis elegans, typically to sort worms based on expression of a fluorescent reporter. Here, we highlight an alternative usage of this instrument, for sorting worms according to their degree of colonization by a GFP-expressing pathogen. This new usage allowed us to address the relationship between colonization of the worm intestine and induction of immune responses. While C. elegans immune responses to different pathogens have been documented, it is still unknown what initiates them. The two main possibilities (which are not mutually exclusive) are recognition of pathogen-associated molecular patterns, and detection of damage caused by infection. To differentiate between the two possibilities, exposure to the pathogen must be dissociated from the damage it causes. The wormsorter enabled separation of worms that were extensively-colonized by the Gram-negative pathogen Pseudomonas aeruginosa, with the damage likely caused by pathogen load, from worms that were similarly exposed, but not, or marginally, colonized. These distinct populations were used to assess the relationship between pathogen load and the induction of transcriptional immune responses. The results suggest that the two are dissociated, supporting the possibility of pathogen recognition.

Automated Separation of C. elegans Variably Colonized by a Bacterial Pathogen

The wormsorter facilitates genetic screens in Caenorhabditis elegans by sorting worms according to expression of fluorescent reporters. Here, we describe a new usage:&#160;sorting according to colonization by a GFP-expressing pathogen, and we employ it to examine the poorly understood role of pathogen recognition in initiating immune responses.

The wormsorter is an instrument analogous to a FACS machine that is used in studies of Caenorhabditis elegans, typically to sort worms based on expression ...

A Microscopic Phenotypic Assay for the Quantification of Intracellular Mycobacteria Adapted for High-throughput/High-content Screening

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since several decades, the sudden burst of multi- and extensively-drug resistant strains is a serious threat for the control of tuberculosis. Therefore, it is essential to identify new targets and pathways critical for the causative agent of the tuberculosis, Mycobacterium tuberculosis (Mtb) and to search for novel chemicals that could become TB drugs. One approach is to set&#160;up methods suitable for the genetic and chemical screens of large scale libraries enabling the search of a needle in a haystack. To this end, we developed a phenotypic assay relying on the detection of fluorescently labeled Mtb within fluorescently labeled host&#160;cells using automated confocal microscopy. This in vitro assay allows an image based quantification of the colonization process of Mtb&#160;into the host and was optimized for the 384-well microplate format, which is proper for screens of siRNA-, chemical compound- or Mtb mutant-libraries. The images are then processed for multiparametric analysis, which provides read&#160;out inferring on the pathogenesis of Mtb&#160;within host cells.

Here, we describe a phenotypic assay applicable to the High-throughput/High-content screens of small-interfering synthetic RNA (siRNA), chemical compound, and Mycobacterium tuberculosis mutant libraries. This method relies on the detection of fluorescently labeled Mycobacterium tuberculosis within fluorescently labeled host&#160;cell using automated confocal microscopy.

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since ...

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying Salmonella-host interactions are&#160;important to elucidate the molecular pathogenesis of Salmonella infection. The Gentamicin protection assay to phenotype Salmonella association, invasion and replication in phagocytic cells was adapted to allow high-throughput screening to define the roles of deletion mutants of Salmonella enterica serotype Typhimurium in host interactions using RAW 264.7 murine macrophages. Under this protocol, the variance in measurements is significantly reduced compared to the standard protocol, because wild-type and multiple mutant strains can be tested in the same culture dish and at the same time. The use of multichannel pipettes increases the throughput and enhances precision. Furthermore, concerns related to using less host cells per well in 96-well culture dish were addressed. Here, the protocol of the modified in vitro Salmonella invasion assay using phagocytic cells was successfully employed to phenotype 38 individual Salmonella deletion mutants for association, invasion and intracellular replication. The in vitro phenotypes are presented, some of which were subsequently confirmed to have in vivo phenotypes in an animal model. Thus, the modified, standardized assay to phenotype Salmonella association, invasion and replication in macrophages with high-throughput capacity could be utilized more broadly to study bacterial-host interactions.

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

A high-throughput assay to in vitro phenotype Salmonella or other bacterial association, invasion, and replication in phagocytic cells with high-throughput capacity was developed. The method was employed to evaluate Salmonella gene knockout mutant strains for their involvements in host-pathogen interactions.

Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying ...

High-throughput Quantitative Real-time RT-PCR Assay for Determining Expression Profiles of Types I and III Interferon Subtypes

Described in this report is a qRT-PCR assay for the analysis of seventeen human IFN subtypes in a 384-well plate format that incorporates highly specific locked nucleic acid (LNA) and molecular beacon (MB) probes, transcript standards, automated multichannel pipetting, and plate drying. Determining expression among the type I interferons (IFN), especially the twelve IFN-&#945; subtypes, is limited by their shared sequence identity; likewise, the sequences of the type III IFN, especially IFN-&#955;2 and -&#955;3, are highly similar. This assay provides a reliable, reproducible, and relatively inexpensive means to analyze the expression of the seventeen interferon subtype transcripts.

This protocol describes a high-throughput qRT-PCR assay for the analysis of type I and III IFN expression signatures. The assay discriminates single base pair differences between the highly similar transcripts of these genes. Through batch assembly and robotic pipetting, the assays are consistent and reproducible.

Described in this report is a qRT-PCR assay for the analysis of seventeen human IFN subtypes in a 384-well plate format that incorporates highly specific ...

Establishment of a High-throughput Setup for Screening Small Molecules That Modulate c-di-GMP Signaling in Pseudomonas aeruginosa

Bacterial resistance to traditional antibiotics has driven research attempts to identify new drug targets in recently discovered regulatory pathways. Regulatory systems that utilize intracellular cyclic di-GMP (c-di-GMP) as a second messenger are one such class of target. c-di-GMP is a signaling molecule found in almost all bacteria that acts to regulate an extensive range of processes including antibiotic resistance, biofilm formation and virulence. The understanding of how c-di-GMP signaling controls aspects of antibiotic resistant biofilm development has suggested approaches whereby alteration of the cellular concentrations of the nucleotide or disruption of these signaling pathways may lead to reduced biofilm formation or increased susceptibility of the biofilms to antibiotics. We describe a simple high-throughput bioreporter protocol, based on green fluorescent protein (GFP), whose expression is under the control of the c-di-GMP responsive promoter cdrA, to rapidly screen for small molecules with the potential to modulate c-di-GMP cellular levels in Pseudomonas aeruginosa (P. aeruginosa). This simple protocol can screen upwards of 3,500 compounds within 48 hours and has the ability to be adapted to multiple microorganisms.

Establishment of a High-throughput Setup for Screening Small Molecules That Modulate c-di-GMP Signaling in Pseudomonas aeruginosa

This article describes the high-throughput assay that has been successfully established to screen large libraries of small molecules for their potential ability to manipulate cellular levels of cyclic di-GMP in Pseudomonas aeruginosa, providing a new powerful tool for antibacterial drug discovery and compound testing.

Bacterial resistance to traditional antibiotics has driven research attempts to identify new drug targets in recently discovered regulatory pathways. ...

A Fluorescence-based Lymphocyte Assay Suitable for High-throughput Screening of Small Molecules

High-throughput screening (HTS) is currently the mainstay for the identification of chemical entities capable of modulating biochemical reactions or cellular processes. With the advancement of biotechnologies and the high translational potential of small molecules, a number of innovative approaches in drug discovery have evolved, which explains the resurgent interest in the use of HTS. The oncology field is currently the most active research area for drug screening, with no major breakthrough made for the identification of new immunomodulatory compounds targeting transplantation-related complications or autoimmune ailments. Here, we present a novel in vitro murine fluorescent-based lymphocyte assay easily adapted for the identification of new immunomodulatory compounds. This assay uses T or B cells derived from a transgenic mouse, in which the Nur77 promoter drives GFP expression upon T- or B-cell receptor stimulation. As the GFP intensity reflects the activation/transcriptional activity of the target cell, our assay defines a novel tool to study the effect of given compound(s) on cellular/biological responses. For instance, a primary screening was performed using 4,398 compounds in the absence of a &#34;target hypothesis&#34;, which led to the identification of 160 potential hits displaying immunomodulatory activities. Thus, the use of this assay is suitable for drug discovery programs exploring large chemical libraries prior to further in vitro/in vivo validation studies.

We present in the current study a novel fluorescence-based assay using lymphocytes derived from a transgenic mouse. This assay is suitable for high-throughput screening (HTS) of small molecules endowed with the capacity of either inhibiting or promoting lymphocyte activation.

High-throughput screening (HTS) is currently the mainstay for the identification of chemical entities capable of modulating biochemical reactions or ...

Cell-free Biochemical Fluorometric Enzymatic Assay for High-throughput Measurement of Lipid Peroxidation in High Density Lipoprotein

Low high-density lipoprotein cholesterol (HDL-C) levels are one of the most powerful independent negative predictors of atherosclerotic cardiovascular disease (CVD). The structure and function of HDL rather than HDL-C may more accurately predict atherosclerosis. Several HDL protein and lipid compositional changes that impair HDL function occur in inflammatory states such as atherosclerosis. HDL function is usually determined by cell based assays such as cholesterol efflux assay but these assays have numerous drawbacks lack of standardization. Cell-free assays may give more robust measures of HDL function compared to cell-based assays. HDL oxidation impairs HDL function. HDL has a major role in lipid peroxide transport and high amount of lipid peroxides is related to abnormal HDL function. Lipid-probe interactions should be considered when interpreting the results of non-enzymatic fluorescence assays for measuring the lipid oxidative state. This motivated us to develop a cell-free biochemical enzymatic method to assess HDL lipid peroxide content (HDLox) that contributes to HDL dysfunction. This method is based on the enzyme horseradish peroxidase (HRP) and the fluorochrome Amplex Red that can quantify (without cholesterol oxidase) the lipid peroxide content per mg of HDL-C. Here a protocol is describedfor determination of HDL-lipid peroxidation using the fluorochrome reagent. Assay variability can be reduced by strict standardization of experimental conditions. Higher HDLox values are associated with reduced HDL antioxidant function. The readout of this assay is associated with readouts of validated cell-based assays, surrogate measures of cardiovascular disease, systemic inflammation, immune dysfunction, and associated cardiovascular and metabolic risk phenotypes. This technical approach is a robust method to assess HDL function in human disease where systemic inflammation, oxidative stress and oxidized lipids have a key role (such as atherosclerosis).

We describe here a fluorometric cell-free biochemical assay for determination of HDL-lipid peroxidation. This rapid and reproducible assay can be used to determine HDL function in large scale studies and can contribute to our understanding of HDL function in human disease.

Low high-density lipoprotein cholesterol (HDL-C) levels are one of the most powerful independent negative predictors of atherosclerotic cardiovascular ...

A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.

Fecal-oral transmission of acute gastroenteritis occurs from time to time, especially when people who handled food and water are infected by Salmonella spp./Shigella spp. The gold standard method for the detection of Salmonella spp./Shigella spp. is direct culture but this is labor-intensive and time-consuming. Here, we describe a high-throughput platform for Salmonella spp./Shigella spp. screening, using real-time polymerase chain reaction (PCR) combined with guided culture. There are two major stages: real-time PCR and the guided culture. For the first stage (real-time PCR), we explain each step of the method: sample collection, pre-enrichment, DNA extraction and real-time PCR. If the real-time PCR result is positive, then the second stage (guided culture) is performed: selective culture, biochemical identification and serological characterization. We also illustrate representative results generated from it. The protocol described here would be a valuable platform for the rapid, specific, sensitive and high-throughput screening of Salmonella spp./Shigella spp.

A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.

Salmonella spp./Shigella spp. are common pathogens attributed to diarrhea. Here, we describe a high-throughput platform for the screening of Salmonella spp./Shigella spp. using real-time PCR combined with guided culture.

Fecal-oral transmission of acute gastroenteritis occurs from time to time, especially when people who handled food and water are infected by Salmonella ...

Automated Behavioral Analysis of Large C. elegans Populations Using a Wide Field-of-view Tracking Platform

Caenorhabditis elegans is a well-established animal model in biomedical research, widely employed in functional genomics and ageing studies. To assess the health and fitness of the animals under study, one typically relies on motility readouts, such as the measurement of the number of body bends or the speed of movement. These measurements usually involve manual counting, making it challenging to obtain good statistical significance, as time and labor constraints often limit the number of animals in each experiment to 25 or less. Since high statistical power is necessary to obtain reproducible results and limit false positive and negative results when weak phenotypic effects are investigated, efforts have recently been made to develop automated protocols focused on increasing the sensitivity of motility detection and multi-parametric behavioral profiling. In order to extend the limit of detection to the level needed to capture the small phenotypic changes that are often crucial in genetic studies and drug discovery, we describe here a technological development that enables the study of up to 5,000 individual animals simultaneously, increasing the statistical power of the measurements by about 1,000-fold compared to manual assays and about 100-fold compared to other available automated methods.

Automated Behavioral Analysis of Large C. elegans Populations Using a Wide Field-of-view Tracking Platform

We describe protocols for using the wide field-of-view nematode tracking platform (WF-NTP), which enables high-throughput phenotypic characterization of large populations of Caenorhabditis elegans. These protocols can be used to characterize subtle behavioral changes in mutant strains or in response to pharmacological treatment in a highly scalable fashion.

Caenorhabditis elegans is a well-established animal model in biomedical research, widely employed in functional genomics and ageing studies. To assess the ...

A High-throughput Shigella-specific Bactericidal Assay

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing activity by assessing the ability of antibodies in serum to bind to bacteria and activate complement. This complement activation results in the lysis and killing of the target bacteria. These assays are valuable because they go beyond quantifying antibody production to elucidate the biological functions that these antibodies have, allowing researchers to study the role that antibodies may play in preventing infection. SBAs have been used to study immune responses for many human pathogens, but there is no widely accepted methodology for Shigella at present. Historically, SBAs have been very labor-intensive, requiring many time-consuming steps to accurately quantify surviving bacteria. This protocol describes a simple, robust, and high-throughput assay that measures functional antibodies specific for Shigella in serum in vitro. The method described here offers many advantages over traditional SBAs, including the use of frozen bacterial stocks, 96 well assay plates, a micro-culture system, and automated colony-counting. All of these modifications make this assay less labor-intensive and more high-throughput. This protocol is simpler and faster to perform than traditional SBAs while still using simple technologies and readily available reagents. The protocol has been successfully applied in multiple independent laboratories and the assay is robust and reproducible. The assay can be used to assess immune responses in pre-clinical as well as clinical studies. Quantifying shigellacidal antibody titers both before and after antigen exposure (either by immunization or infection) allows for a broader understanding of how functional antibody responses are generated and their contribution to protective immunity. The development of this standardized, well-characterized assay may greatly facilitate Shigella vaccine design.

A High-throughput Shigella-specific Bactericidal Assay

Here we present a protocol to measure Shigellacidal activity of antibodies in serum. Serum is mixed with bacteria and exogenous complement, incubated, and the reaction mixture is plated on agar plates. Viable bacteria form colonies which are counted, using an automated colony enumerator, and used to determine the bactericidal titer.

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing ...