Name: a high-throughput compatible assay to evaluate drug efficacy against macrophage passaged mycobacterium tuberculosis
Uploaded: 2017-03-24T15:00:00
Description: Watch this Scientific Journal Video about A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis at JoVE.com

We thank Dr. Frank Wolschendorf for access to the Cytation 3 automated imaging plate reader. This work was funded in part by NIH grant R01-AI104499 to OK. Parts of the work were performed in the UAB CFAR facilities and by the UAB CFAR Flow Cytometry Core/Joint UAB Flow Cytometry Core, which are funded by NIH/NIAID P30 AI027767 and by NIH 5P30 AR048311.

NOTE: As M. tuberculosis mc26206 is an avirulent strain17,18, all work in this protocol can be performed in a Biosafety Level 2 facility (BSL-2).
1. Culture Conditions for Green Fluorescent Protein Expressing M. tuberculosis mc26206 (Mtb-GFP)
NOTE: The M. tuberculosis H37Rv derived auxotroph strain mc26206 (&#916;panCD, &#916;leu...

<ol>
	<li>Barry, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lessons+from+seven+decades+of+antituberculosis+drug+discovery.">Lessons from seven decades of antituberculosis drug discovery.</a> Curr Top Med Chem. 11 (10), 1216-1225 (2011).</li><li>Bass, J. B., 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=Treatment+of+tuberculosis+and+tuberculosis+infection+in+adults+and+children.+American+Thoracic+Society+and+The+Centers+for+Disease+Control+and+Prevention.">Treatment of tuberculosis and tuberculosis infection in adults and children. American Thoracic Society and The Centers for Disease Control and Prevention.</a> Am J Respir Crit Care Med. 149 (5), 1359-1374 (1994).</li><li>Koul, A., Arnoult, E., Lounis, N., Guillemont, J., Andries, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+challenge+of+new+drug+discovery+for+tuberculosis.">The challenge of new drug discovery for tuberculosis.</a> Nature. 469 (7331), 483-490 (2011).</li><li>Palomino, J. C., Martin, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TMC207+becomes+bedaquiline,+a+new+anti-TB+drug.">TMC207 becomes bedaquiline, a new anti-TB drug.</a> Future Microbiol. 8 (9), 1071-1080 (2013).</li><li>Zuniga, E. S., Early, J., Parish, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+future+for+early-stage+tuberculosis+drug+discovery.">The future for early-stage tuberculosis drug discovery.</a> Future Microbiol. 10 (2), 217-229 (2015).</li><li>Evangelopoulos, D., Fonseca, d. a., D, J., Waddell, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+anti-tuberculosis+drug+efficacy:+rethinking+bacterial+populations+and+how+we+model+them.">Understanding anti-tuberculosis drug efficacy: rethinking bacterial populations and how we model them.</a> Int J Infect Dis. 32, 76-80 (2015).</li><li>Ekins, 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=Looking+back+to+the+future:+predicting+in+vivo+efficacy+of+small+molecules+versus+Mycobacterium+tuberculosis.">Looking back to the future: predicting in vivo efficacy of small molecules versus Mycobacterium tuberculosis.</a> J Chem Inf Model. 54 (4), 1070-1082 (2014).</li><li>Christophe, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+content+screening+identifies+decaprenyl-phosphoribose+2'+epimerase+as+a+target+for+intracellular+antimycobacterial+inhibitors.">High content screening identifies decaprenyl-phosphoribose 2' epimerase as a target for intracellular antimycobacterial inhibitors.</a> PLoS Pathog. 5 (10), e1000645 (2009).</li><li>Hartkoorn, R. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+drug+susceptibility+of+intracellular+and+extracellular+tuberculosis,+and+the+impact+of+P-glycoprotein.">Differential drug susceptibility of intracellular and extracellular tuberculosis, and the impact of P-glycoprotein.</a> Tuberculosis (Edinb). 87 (3), 248-255 (2007).</li><li>Queval, C. 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+microscopic+phenotypic+assay+for+the+quantification+of+intracellular+mycobacteria+adapted+for+high-throughput/high-content+screening.">A microscopic phenotypic assay for the quantification of intracellular mycobacteria adapted for high-throughput/high-content screening.</a> J Vis Exp. (83), e51114 (2014).</li><li>Sorrentino, F., 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=Development+of+an+intracellular+screen+for+new+compounds+able+to+inhibit+Mycobacterium+tuberculosis+growth+in+human+macrophages.">Development of an intracellular screen for new compounds able to inhibit Mycobacterium tuberculosis growth in human macrophages.</a> Antimicrob Agents Chemother. 60 (1), (2015).</li><li>Sarathy, J., Dartois, V., Dick, T., Gengenbacher, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduced+drug+uptake+in+phenotypically+resistant+nutrient-starved+nonreplicating+Mycobacterium+tuberculosis.">Reduced drug uptake in phenotypically resistant nutrient-starved nonreplicating Mycobacterium tuberculosis.</a> Antimicrob Agents Chemother. 57 (4), 1648-1653 (2013).</li><li>Dutta, N. K., Karakousis, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Can+the+duration+of+tuberculosis+treatment+be+shortened+with+higher+dosages+of+rifampicin?.">Can the duration of tuberculosis treatment be shortened with higher dosages of rifampicin?.</a> Front Microbiol. 6, 1117 (2015).</li><li>van Ingen, 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=Why+Do+We+Use+600+mg+of+Rifampicin+in+Tuberculosis+Treatment?.">Why Do We Use 600 mg of Rifampicin in Tuberculosis Treatment?.</a> Clin Infect Dis. 52 (9), e194-e199 (2011).</li><li>Donald, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cerebrospinal+fluid+concentrations+of+antituberculosis+agents+in+adults+and+children.">Cerebrospinal fluid concentrations of antituberculosis agents in adults and children.</a> Tuberculosis (Edinb). 90 (5), 279-292 (2010).</li><li>Schaaf, K., 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+Macrophage+Infection+Model+to+Predict+Drug+Efficacy+Against+Mycobacterium+Tuberculosis.">A Macrophage Infection Model to Predict Drug Efficacy Against Mycobacterium Tuberculosis.</a> Assay Drug Dev Technol. 14 (6), 345-354 (2016).</li><li>Sampson, S. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protection+elicited+by+a+double+leucine+and+pantothenate+auxotroph+of+Mycobacterium+tuberculosis+in+guinea+pigs.">Protection elicited by a double leucine and pantothenate auxotroph of Mycobacterium tuberculosis in guinea pigs.</a> Infect Immun. 72 (5), 3031-3037 (2004).</li><li>Jain, 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=Specialized+transduction+designed+for+precise+high-throughput+unmarked+deletions+in+Mycobacterium+tuberculosis.">Specialized transduction designed for precise high-throughput unmarked deletions in Mycobacterium tuberculosis.</a> MBio. 5 (3), e01245-e01214 (2014).</li><li>Davis, J. M., Ramakrishnan, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+the+granuloma+in+expansion+and+dissemination+of+early+tuberculous+infection.">The role of the granuloma in expansion and dissemination of early tuberculous infection.</a> Cell. 136 (1), 37-49 (2009).</li><li>Collins, L., Franzblau, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microplate+alamar+blue+assay+versus+BACTEC+460+system+for+high-throughput+screening+of+compounds+against+Mycobacterium+tuberculosis+and+Mycobacterium+avium.">Microplate alamar blue assay versus BACTEC 460 system for high-throughput screening of compounds against Mycobacterium tuberculosis and Mycobacterium avium.</a> Antimicrob Agents Chemother. 41 (5), 1004-1009 (1997).</li><li>Snewin, V. 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=Assessment+of+immunity+to+mycobacterial+infection+with+luciferase+reporter+constructs.">Assessment of immunity to mycobacterial infection with luciferase reporter constructs.</a> Infect Immun. 67 (9), 4586-4593 (1999).</li></ol>

Here, we have described in detail an alternative Mtb infection model suitable for drug efficacy testing. This model takes into account two key factors that should be given more consideration during the early TB drug development process: the presence of physiologically relevant barriers to drug penetration and metabolic changes of Mtb during infection. While we have previously shown the benefits of our infection model and proposed the possibility of scaling up the infection for throughput compatibility<s...

Tuberculosis (TB) remains a serious global health threat despite the availability of anti-TB chemotherapy regimens for over 40 years1. This is due in part to the requirement for long treatment periods of over 6 months using multiple drug combinations, which leads to patient non-compliance2. The emergence of drug-resistant TB in recent years has further compounded problems in a field where successful development of clinically approved drugs is virtually non-existent3. Indeed, despite exhaustive anti-TB drug development, only a single drug has been FDA approved for clinical use in the past 40 years4. Thus, new generations of anti-TB drugs are urgently needed to address this problem.
A key problem in TB drug discovery is the lack of successful transfer from compounds with in vitro activity to efficacy in the clinical setting5,6,7. Initially, target based approaches were used to screen for anti-Mtb drugs5, which failed to translate into whole bacterial cells. Even when Mtb cells are used, it is often performed using broth grown cultures, which do not accurately predict drug efficacy in vivo8,9. These problems have been recognized and drug screening assays against macrophages containing Mtb or latent Mtb have been successfully established8,10,11,12. However, even these more advanced assays do not give sufficient consideration to the penetration barriers that drugs encounter in the non-vascularized pulmonary lesions, and in the necrotic foci at the site of infection. Indeed, even for the first-line TB drug rifampicin, sub-optimal dosing has been questioned due to inadequate in vivo tissue and cerebral spinal fluid (CSF) penetration13,14,15 as well as decreased efficacy against intracellular Mtb8,9. As such, new models and assays that would take into account these parameters during the early lead development process would undoubtedly improve TB drug discovery efforts.
To address this need, we recently established an inexpensive, rapid, and BSL-2 compatible alternative infection model for Mtb drug efficacy testing16. This infection model produced densely packed Mtb within large macrophage aggregate structures, which recapitulated physiologically relevant cellular penetration barriers and generated macrophage-passaged Mtb with an altered physiological status resembling latent Mtb. Mtb derived from this infection model was combined with the resazurin microtiter assay (REMA) to evaluate drug efficacy, which produced results consistent with other intracellular infection models and correlated well with the reported ability of common TB drugs to achieve high CSF concentrations relative to serum concentrations16.
Here we describe in detail the generation of Mtb/macrophage aggregate structures to produce macrophage-passaged Mtb suitable for drug susceptibility testing using REMA. In particular, we show how this infection system could be adapted to a 96-well format for compatibility with throughput screening of candidate anti-TB drugs.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>7H9</td>
			<td>BD Difco</td>
			<td>271310</td>
			<td>Follow manufacturer&#39;s recommendations</td>
		</tr>
		<tr>
			<td>Middlebrook OADC</td>
			<td>BD Biosciences</td>
			<td>212351</td>
			<td></td>
		</tr>
		<tr>
			<td>Tyloxapol</td>
			<td>Sigma</td>
			<td>T8761</td>
			<td>Prepare 20% stock solution in H2O; filter sterilize</td>
		</tr>
		<tr>
			<td>D-Pantothenic acid hemicalcium salt</td>
			<td>Sigma</td>
			<td>P5710</td>
			<td>Prepare 24 mg/ml&#160; stock solution in H2O; filter sterilize</td>
		</tr>
		<tr>
			<td>L-leucine</td>
			<td>MP Biomedicals</td>
			<td>194694</td>
			<td>Prepare 50 mg/ml&#160; stock solution in H2O; filter sterilize</td>
		</tr>
		<tr>
			<td>Hygromycin B</td>
			<td>EMD Millipore</td>
			<td>400051</td>
			<td>Prepare 200 mg/ml&#160; stock solution in H2O</td>
		</tr>
		<tr>
			<td>Nalgene Square PETG media bottle</td>
			<td>Thermo Fisher</td>
			<td>2019-0030</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI 1640 media</td>
			<td>Hyclone</td>
			<td>SH30027.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Atlanta Biologicals</td>
			<td>S12450H</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamine</td>
			<td>Corning</td>
			<td>MT25005CI</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Hyclone</td>
			<td>SH30237.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Cytation 3 plate reader</td>
			<td>Biotek</td>
			<td></td>
			<td>Interchangable with any fluorescent plate reader and microscope</td>
		</tr>
		<tr>
			<td>Gen5 Software</td>
			<td>Biotek</td>
			<td></td>
			<td>Recording and analysis of rezasurin coversion</td>
		</tr>
		<tr>
			<td>Rifampicin&#160;</td>
			<td>Fisher Scientific</td>
			<td>BP2679250</td>
			<td>Prepare 10 mg/ml stock solution in H2O</td>
		</tr>
		<tr>
			<td>Moxifloxacin Hydrochloride</td>
			<td>Acros Organics</td>
			<td>457960010</td>
			<td>Prepare 10 mg/ml stock solution in H2O</td>
		</tr>
		<tr>
			<td>Resazurin Sodium Salt</td>
			<td>Sigma</td>
			<td>R7017</td>
			<td>Prepare 800 &#956;g/mL stock solution in H2O; filter sterilize</td>
		</tr>
		<tr>
			<td>Tween-80</td>
			<td>Fisher Scientific</td>
			<td>T164500</td>
			<td>Prepare 20% stock solution in H2O; filter sterilize</td>
		</tr>
	</tbody>
</table>

a high-throughput compatible assay to evaluate drug efficacy against macrophage passaged mycobacterium tuberculosis

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to effectiveness in the clinical setting. This is likely due to a lack of consideration for the physiologically relevant cellular penetration barriers that exist in the infected host. We recently established an alternative infection model that generates large macrophage aggregate structures containing densely packed M. tuberculosis (Mtb) at its core, which was suitable for drug susceptibility testing. This infection model is inexpensive, rapid, and most importantly BSL-2 compatible. Here, we describe the experimental procedures to generate Mtb/macrophage aggregate structures that would produce macrophage-passaged Mtb for drug susceptibility testing. In particular, we demonstrate how this infection system could be directly adapted to the 96-well plate format showing throughput capability for the screening of compound libraries against Mtb. Overall, this assay is a valuable addition to the currently available Mtb drug discovery toolbox due to its simplicity, cost effectiveness, and scalability.

To confirm the robustness of adapting this infection model to 96-well plate format, we here examined the drug susceptibility of Mtb derived from our 96-well adapted infection model to rifampicin (RIF) and moxifloxacin (MOXI) according to the template given in Figure 1A. We demonstrate that the generation of Mtb/macrophage aggregate structures key to this assay can be reliably produced in a 96-well plate format (Figure 2), thereby enablin...

Watch this Scientific Journal Video about A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis at JoVE.com

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

New models and assays that would improve the early drug development process for next-generation anti-tuberculosis drugs are highly desirable. Here, we describe a quick, inexpensive, and BSL-2 compatible assay to evaluate drug efficacy against Mycobacterium tuberculosis that can be easily adapted for high-throughput screening.

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to ...

The overall goal of this procedure is to reproducibly generate mycobacterium tuberculosis infected macrophage aggregate structures in 96 well plate format for drug susceptibility testing using a viability dye. This method can improve the early drug development process for anti tuberculosis compounds, which is hindered by the unproductive translation of candidate compounds into the clinical setting. The main advantage of this simple, inexpensive, BSL two compatible infection model is that it recapitulates physiologically relevant cellular penetration barriers, reminiscent of tuberculosis granulomas.This produces drug susceptibility results more predictive of in vivo efficacy. Begin this procedure by preparing green fluorescent protein expressing M.tuberculosis MC squared 6206, hereafter referred to as MTBGFP, for infection. Keep in mind that this is avirulent strain, so all work in the protocol described here can be performed in a biosafety level two facility.For each 96 well plate to be set up centrifuge at 2.8 times 10 to the eighth MTBGFP at 3, 200 times G for five minutes in a swinging bucket centrifuge. After the spin, aspirate the supernatant and add five milliliters of RPMIC to wash the bacteria. Pipette up and down to resuspend the cell.Then centrifuge again. After the second spin pour off the supernatant and resuspend the bacterial cells in seven milliliters of RPMIC, then vortex for 10 seconds. Next, for each 96 well plate to be set up, centrifuge seven times 10 to the sixth THP1 human monocytic cells at 250 times G for five minutes.After the centrifugation pour off the supernatant and resuspend the THP1 cells in seven milliliters of RPMIC. Next prepare a 96 well plate for infection by adding 200 microliters of sterile water to the wells in rows A and H and columns one and 12. This water rim will prevent the evaporation of culture medium.Add 200 microliters of RPMIC to column two, B two to G two, for the background control or blank. To infect the THP1 monocyte use a pipette to transfer the entire prepared MTBGFP bacterial suspension to the THP1 cell suspension and mix will by pipetting up and down. The final THP1 cell density is five times 10 to the fifth per milliliter and the corresponding well duplicity of infection is 40.Next, pour the THP1 MTBGFP suspension into a 25 milliliter reservoir, and then using a multichannel pipette, add 200 microliters of THP1 MTBGFP suspension all of the remaining 96 wells, E three through G 11. Incubate the plate at 37 degrees Celsius, with 5%CO2 for seven to 10 days. Every two days throughout the incubation, use a multichannel pipette to change the medium by slowly removing 100 microliters of spent medium from the top of each well and gently adding 100 microliters of pre warmed RPMIC.When changing the medium it is important to take care not to disturb the MTB macrophage aggregates on the bottom of the wells. Each day visually examine the wells using a fluorescence microscope, equipped with bright field and GFP filter sets with a four to 10 X objective. Note the size of MTB macrophage aggregates and capture images if desired.By day seven to 10 MTB macrophage aggregates should be sufficiently large to proceed for drug efficacy testing, as described later in the video. For drug testing, prepare two anti tuberculosis drugs in triplicate on a new 96 well plate as follows. First, add 125 microliters of 7H9C medium to wells B two through G 10.Next prepare the two drugs at double the highest desired final concentration in one milliliter of 7H9C. Using a pipette add 250 microliters of each drug to wells B, C, and D 11 and then E, F, and G 11 respectively for triplicate treatments. Next, using a multichannel pipette serially dilute the test drugs two fold by moving 125 microliters from B 11 through G 11 into B 10 through G 10.Mix by pipetting five times at each step. Continue to move 125 microliters from column to column right to left across the plate, and stop after column four. After mixing column four discard 125 microliters into a waste container.Columns two and three should not contain any drugs. This will allow them to be used as a background, and for positive growth controls. Next retrieve the 96 well plate containing the MTB infected macrophages from the incubator.Without tilting the plate, use a multichannel pipette to remove 150 microliters of medium from wells B two through G 11. Then tilt the plate as shown here, and insert the pipette tips into the bottom edge of the wells and remove the remaining medium, about 50 microliters. As MTB macrophage aggregates adhere to the bottom of the well, no material should be lost.However, removal of the medium should be as gentle as possible and care must be taken to avoid resuspension during this process. Gently add 100 microliters of 7H9C medium to wells B two through G 11 of the plate, which contain the MTB macrophage aggregates. Using a multichannel pipette transfer 100 microliters of the drug containing 96 well plate to the corresponding wells of the infection plate.Then place the plate in a sealed bag and incubate it for three days at 37 degrees Celsius. The resazurin assay relies on the oxidative species produced by metabolically active MTB to convert the blue resazurin to fluorescent pink resorufin. The change in color and fluorescence can be used as a surrogate marker to determine the amount of bacterial growth.Prepare a stock solution of resazurin at a final concentration of 8 milligrams per milliliter in water. Filter through a 22 micrometer pore size PVDF membrane for sterilization. Prepare a working solution in resazurin by mixing the stock solution, water, and Tween-80 in a two to one to one ratio.Final concentrations are 4 milligrams per milliliter resazurin, and 5%Tween-80. Using a plate reader, set up a program to read the fluorescence at 530 nanometer excitation and 590 nanometer emission for 24 hours every 30 minutes at 37 degrees Celsius. Pre warm the plate reader to 37 degrees Celsius.Using a multichannel pipette, add 20 microliters of resazurin working solution to wells B two through G 11 of the drug treated plate. Place the plate on the reader and start the program. To confirm the robustness of adapting this infection model to 96 well plate format the susceptibility of MTB rifampicin RIF in moxifloxacin moxy was assessed as described in this video.As shown here, MTB macrophage aggregate structures were successfully generated in a 96 well plate format thereby enabling through put compatibility. To quantitatively measure the conversion of resazurin as an indicator of bacterial growth fluorescence of individual wells was monitored kinetically for 24 hours. The presence of viable MTB cells is determined by the conversion of the blue resazurin dye to its pink reduced form, which is quantitatively reflected by the relative fluorescence z nets at the time point of saturation.These representative mini graphs show the resulting fluorescence units shown on the Y axis versus time shown on the X axis. To generate drug susceptibility killing curves rifampicin and moxifloxacin treated wells were normalized to the no drug control maximal MTB growth as 100%survival. Background control blank signals were subtracted from every sample well.The percent survival was plotted for each individual concentration of drug treatment to generate a killing curve. These data show that the minimal inhibitory concentration defines the lowest concentration of the antibiotic at which 90%growth inhibition is observed is greater than two micrograms per milliliter, for both rifampicin and moxifloxacin against MTB derived from our infection model. As such, the minimal inhibitory concentration of these two drugs against MTB using our infection model and assay is more reflective of the activity of these drugs in vivo.After watching this video, you should have a good understanding of how to reliably and reproducibly generate MTB infected macrophage aggregate structures for drug susceptibility testing using the resazurin assay. Following this procedure modifying the drug template from two drugs as shown to a 58 drug library panel is easily performed to enable high through put drug screening.

a-high-throughput-compatible-assay-to-evaluate-drug-efficacy-against

Research

JoVE Journal

Immunology and Infection

Growth of Mycobacterium tuberculosis Biofilms

Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, has an extraordinary ability to survive against environmental stresses including antibiotics. Although stress tolerance of M. tuberculosis is one of the likely contributors to the 6-month long chemotherapy of tuberculosis 1, the molecular mechanisms underlying this characteristic phenotype of the pathogen remain unclear. Many microbial species have evolved to survive in stressful environments by self-assembling in highly organized, surface attached, and matrix encapsulated structures called biofilms 2-4. Growth in communities appears to be a preferred survival strategy of microbes, and is achieved through genetic components that regulate surface attachment, intercellular communications, and synthesis of extracellular polymeric substances (EPS) 5,6. The tolerance to environmental stress is likely facilitated by EPS, and perhaps by the physiological adaptation of individual bacilli to heterogeneous microenvironments within the complex architecture of biofilms 7.
In a series of recent papers we established that M. tuberculosis and Mycobacterium smegmatis have a strong propensity to grow in organized multicellular structures, called biofilms, which can tolerate more than 50 times the minimal inhibitory concentrations of the anti-tuberculosis drugs isoniazid and rifampicin 8-10. M. tuberculosis, however, intriguingly requires specific conditions to form mature biofilms, in particular 9:1 ratio of headspace: media as well as limited exchange of air with the atmosphere 9. Requirements of specialized environmental conditions could possibly be linked to the fact that M. tuberculosis is an obligate human pathogen and thus has adapted to tissue environments. In this publication we demonstrate methods for culturing M. tuberculosis biofilms in a bottle and a 12-well plate format, which is convenient for bacteriological as well as genetic studies. We have described the protocol for an attenuated strain of M. tuberculosis, mc27000, with deletion in the two loci, panCD and RD1, that are critical for in vivo growth of the pathogen 9. This strain can be safely used in a BSL-2 containment for understanding the basic biology of the tuberculosis pathogen thus avoiding the requirement of an expensive BSL-3 facility. The method can be extended, with appropriate modification in media, to grow biofilm of other culturable mycobacterial species.
Overall, a uniform protocol of culturing mycobacterial biofilms will help the investigators interested in studying the basic resilient characteristics of mycobacteria. In addition, a clear and concise method of growing mycobacterial biofilms will also help the clinical and pharmaceutical investigators to test the efficacy of a potential drug.

Growth of Mycobacterium tuberculosis Biofilms

Mycobacterium tuberculosis forms drug tolerant biofilms when cultured in certain conditions. Here we describe methods for culturing M. tuberculosis biofilms and determining the frequency of drug tolerant persisters. These protocols will be useful for further studies into the mechanisms of drug tolerance in M. tuberculosis.

Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, has an extraordinary ability to survive against environmental stresses including ...

An Experimental Model to Study Tuberculosis-Malaria Coinfection upon Natural Transmission of Mycobacterium tuberculosis and Plasmodium berghei

Coinfections naturally occur due to the geographic overlap of distinct types of pathogenic organisms. Concurrent infections most likely modulate the respective immune response to each single pathogen and may thereby affect pathogenesis and disease outcome. Coinfected patients may also respond differentially to anti-infective interventions. Coinfection between tuberculosis as caused by mycobacteria and the malaria parasite Plasmodium, both of which are coendemic in many parts of sub-Saharan Africa, has not been studied in detail. In order to approach the challenging but scientifically and clinically highly relevant question how malaria-tuberculosis coinfection modulate host immunity and the course of each disease, we established an experimental mouse model that allows us to dissect the elicited immune responses to both pathogens in the coinfected host. Of note, in order to most precisely mimic naturally acquired human infections, we perform experimental infections of mice with both pathogens by their natural routes of infection, i.e. aerosol and mosquito bite, respectively.

An Experimental Model to Study Tuberculosis-Malaria Coinfection upon Natural Transmission of Mycobacterium tuberculosis and Plasmodium berghei

Tuberculosis and malaria are two of the most prevalent infections in humans and major causes of morbidity and mortality in impoverished populations in the tropics. We established an experimental model system to study outcome of malaria-tuberculosis coinfection in mice after challenge with both pathogens via their natural route of infection.

Coinfections naturally occur due to the geographic overlap of distinct types of pathogenic organisms. Concurrent infections most likely modulate the ...

Demonstrating a Multi-drug Resistant Mycobacterium tuberculosis Amplification Microarray

Simplifying microarray workflow is a necessary first step for creating MDR-TB microarray-based diagnostics that can be routinely used in lower-resource environments. An amplification microarray combines asymmetric PCR amplification, target size selection, target labeling, and microarray hybridization within a single solution and into a single microfluidic chamber. A batch processing method is demonstrated with a 9-plex asymmetric master mix and low-density gel element microarray for genotyping multi-drug resistant Mycobacterium tuberculosis (MDR-TB). The protocol described here can be completed in 6 hr and provide correct genotyping with at least 1,000 cell equivalents of genomic DNA. Incorporating on-chip wash steps is feasible, which will result in an entirely closed amplicon method and system. The extent of multiplexing with an amplification microarray is ultimately constrained by the number of primer pairs that can be combined into a single master mix and still achieve desired sensitivity and specificity performance metrics, rather than the number of probes that are immobilized on the array. Likewise, the total analysis time can be shortened or lengthened depending on the specific intended use, research question, and desired limits of detection. Nevertheless, the general approach significantly streamlines microarray workflow for the end user by reducing the number of manually intensive and time-consuming processing steps, and provides a simplified biochemical and microfluidic path for translating microarray-based diagnostics into routine clinical practice.

Demonstrating a Multi-drug Resistant Mycobacterium tuberculosis Amplification Microarray

An amplification microarray combines asymmetric PCR amplification and microarray hybridization into a single chamber, which significantly streamlines microarray workflow for the end user. Simplifying microarray workflow is a necessary first step for creating microarray-based diagnostics that can be routinely used in lower-resource environments.

Simplifying microarray workflow is a necessary first step for creating MDR-TB microarray-based diagnostics that can be routinely used in lower-resource ...

Establishment and Optimization of a High Throughput Setup to Study Staphylococcus epidermidis and Mycobacterium marinum Infection as a Model for Drug Discovery

Zebrafish are becoming a valuable tool in the preclinical phase of drug discovery screenings as a whole animal model with high throughput screening possibilities. They can be used to bridge the gap between cell based assays at earlier stages and in vivo validation in mammalian models, reducing, in this way, the number of compounds passing through to testing on the much more expensive rodent models. In this light, in the present manuscript is described a new high throughput pipeline using zebrafish as in vivo model system for the study of Staphylococcus epidermidis and Mycobacterium marinum infection. This setup allows the generation and analysis of large number of synchronous embryos homogenously infected. Moreover the flexibility of the pipeline allows the user to easily implement other platforms to improve the resolution of the analysis when needed. The combination of the zebrafish together with innovative high throughput technologies opens the field of drug testing and discovery to new possibilities not only because of the strength of using a whole animal model but also because of the large number of transgenic lines available that can be used to decipher the mode of action of new compounds.

Establishment and Optimization of a High Throughput Setup to Study Staphylococcus epidermidis and Mycobacterium marinum Infection as a Model for Drug Discovery

This video article describes the high throughput pipeline that has been successfully established to infect and analyze large numbers of zebrafish embryos providing a new powerful tool for compound testing and drug discovery using a whole animal vertebrate organism.

Zebrafish are becoming a valuable tool in the preclinical phase of drug discovery screenings as a whole animal model with high throughput screening ...

A Novel Microdissection Approach to Recovering Mycobacterium tuberculosis Specific Transcripts from Formalin Fixed Paraffin Embedded Lung Granulomas

Microdissection has been used for the examination of tissues at DNA, RNA, and protein levels for over a decade. Laser capture microscopy (LCM) is the most common microdissection technique used today. In this technique, a laser is used to focally melt a thermoplastic membrane that overlies a dehydrated tissue section1. The tissue section composite is then lifted and separated from the membrane. Although this technique can be used successfully for tissue examination, it is time consuming and expensive. Furthermore, the successful completion of procedures using this technique requires the use of a laser, thus limiting its use. A new more affordable and practical microdissection approach called mesodissection is a possible solution to the pitfalls of LCM. This technique employs the MESO-1/MeSectr system to mill the desired tissue from a slide mounted tissue sample while concurrently dispensing and aspirating fluid to recover the desired tissue sample into a consumable mill bit. Before the dissection process begins, the user aligns the formalin fixed paraffin embedded (FFPE) slide with a hematoxylin and eosin stained (H&#38;E) reference slide. Thereafter, the operator annotates the desired dissection area and proceeds to dissect the appropriate segment. The program generates an archived image of the dissection. The main advantage of mesodissection is the short duration needed to dissect a slide, taking an average of ten minutes from set up to sample generation in this experiment. Additionally, the system is significantly more cost effective and user friendly. A slight disadvantage is that it is not as precise as laser capture microscopy. In this article we demonstrate how mesodissection can be used to extract RNA from slides from FFPE granulomas caused by Mycobacterium tuberculosis (Mtb).

A Novel Microdissection Approach to Recovering Mycobacterium tuberculosis Specific Transcripts from Formalin Fixed Paraffin Embedded Lung Granulomas

Microdissection has been extensively employed for the examination of DNA, RNA, and protein within tissue. Laser capture microscopy (LCM) is the most commonly used method, but a new milling technique, mesodissection, is recently available. We demonstrate RNA extraction from mesodissected formalin fixed paraffin embedded tissue slides of Mycobacterium tuberculosis granulomas.

Microdissection has been used for the examination of tissues at DNA, RNA, and protein levels for over a decade. Laser capture microscopy (LCM) is the most ...

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 ...

A 3D Human Lung Tissue Model for Functional Studies on Mycobacterium tuberculosis Infection

Tuberculosis (TB) still holds a major threat to the health of people worldwide, and there is a need for cost-efficient but reliable models to help us understand the disease mechanisms and advance the discoveries of new treatment options. In vitro cell cultures of monolayers or co-cultures lack the three-dimensional (3D) environment and tissue responses. Herein, we describe an innovative in vitro model of a human lung tissue, which holds promise to be an effective tool for studying the complex events that occur during infection with Mycobacterium tuberculosis (M. tuberculosis). The 3D tissue model consists of tissue-specific epithelial cells and fibroblasts, which are cultured in a matrix of collagen on top of a porous membrane. Upon air exposure, the epithelial cells stratify and secrete mucus at the apical side. By introducing human primary macrophages infected with M. tuberculosis to the tissue model, we have shown that immune cells migrate into the infected-tissue and form early stages of TB granuloma. These structures recapitulate the distinct feature of human TB, the granuloma, which is fundamentally different or not commonly observed in widely used experimental animal models. This organotypic culture method enables the 3D visualization and robust quantitative analysis that provides pivotal information on spatial and temporal features of host cell-pathogen interactions. Taken together, the lung tissue model provides a physiologically relevant tissue micro-environment for studies on TB. Thus, the lung tissue model has potential implications for both basic mechanistic and applied studies. Importantly, the model allows addition or manipulation of individual cell types, which thereby widens its use for modelling a variety of infectious diseases that affect the lungs.

A 3D Human Lung Tissue Model for Functional Studies on Mycobacterium tuberculosis Infection

Human tuberculosis infection is a complex process, which is difficult to model in vitro. Here we describe a novel 3D human lung tissue model that recapitulates the dynamics that occur during infection, including the migration of immune cells and early granuloma formation in a physiological environment.

Tuberculosis (TB) still holds a major threat to the health of people worldwide, and there is a need for cost-efficient but reliable models to help us ...

A Robust Pneumonia Model in Immunocompetent Rodents to Evaluate Antibacterial Efficacy against S. pneumoniae, H. influenzae, K. pneumoniae, P. aeruginosa or A. baumannii

Efficacy of candidate antibacterial treatments must be demonstrated in animal models of infection as part of the discovery and development process, preferably in models which mimic the intended clinical indication. A method for inducing robust lung infections in immunocompetent rats and mice is described which allows for the assessment of treatments in a model of serious pneumonia caused by S. pneumoniae, H. influenzae, P. aeruginosa, K. pneumoniae or A. baumannii. Animals are anesthetized, and an agar-based inoculum is deposited deep into the lung via nonsurgical intratracheal intubation. The resulting infection is consistent, reproducible, and stable for at least 48 h and up to 96 h for most isolates. Studies with marketed antibacterials have demonstrated good correlation between in vivo efficacy and in vitro susceptibility, and concordance between pharmacokinetic/pharmacodynamic targets determined in this model and clinically accepted targets has been observed. Although there is an initial time investment when learning the technique, it can be performed quickly and efficiently once proficiency is achieved. Benefits of the model include elimination of the neutropenic requirement, increased robustness and reproducibility, ability to study more pathogens and isolates, improved flexibility in study design and establishment of a challenging infection in an immunocompetent host.

A Robust Pneumonia Model in Immunocompetent Rodents to Evaluate Antibacterial Efficacy against S. pneumoniae, H. influenzae, K. pneumoniae, P. aeruginosa or  A. baumannii

A method for establishing lung infections in immunocompetent rodents is described. With proficiency, this method can be performed quickly and easily to induce stable infection with many isolates of S. pneumoniae, H. influenzae, P. aeruginosa, K. pneumoniae and A. baumannii.

Efficacy of candidate antibacterial treatments must be demonstrated in animal models of infection as part of the discovery and development process, ...

System for Efficacy and Cytotoxicity Screening of Inhibitors Targeting Intracellular Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a leading cause of morbidity and mortality worldwide. With the increased spread of multi drug-resistant TB (MDR-TB), there is a real urgency to develop new therapeutic strategies against M. tuberculosis infections. Traditionally, compounds are evaluated based on their antibacterial activity under in vitro growth conditions in broth; however, results are often misleading for intracellular pathogens like M. tuberculosis since in-broth phenotypic screening conditions are significantly different from the actual disease conditions within the human body. Screening for inhibitors that work inside macrophages has been traditionally difficult due to the complexity, variability in infection, and slow replication rate of M. tuberculosis. In this study, we report a new approach to rapidly assess the effectiveness of compounds on the viability of M. tuberculosis in a macrophage infection model. Using a combination of a cytotoxicity assay and an in-broth M. tuberculosis viability assay, we were able to create a screening system that generates a comprehensive analysis of compounds of interest. This system is capable of producing quantitative data at a low cost that is within reach of most labs and yet is highly scalable to fit large industrial settings.

System for Efficacy and Cytotoxicity Screening of Inhibitors Targeting Intracellular Mycobacterium tuberculosis

We have developed a modular high-throughput screening system for discovering novel compounds against Mycobacterium tuberculosis, targeting intracellular and in-broth growing bacteria as well as cytotoxicity against the mammalian host cell.

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a leading cause of morbidity and mortality worldwide. With the increased spread ...

Imaging Mycobacterium tuberculosis in Mice with Reporter Enzyme Fluorescence

Reporter enzyme fluorescence (REF) utilizes substrates that are specific for enzymes present in target organisms of interest for imaging or detection by fluorescence or bioluminescence. We utilize BlaC, an enzyme expressed constitutively by all M. tuberculosis strains. REF allows rapid quantification of bacteria in lungs of infected mice. The same group of mice can be imaged at many time points, greatly reducing costs, enumerating bacteria more quickly, allowing novel observations in host-pathogen interactions, and increasing statistical power, since more animals per group are readily maintained. REF is extremely sensitive due to the catalytic nature of the BlaC enzymatic reporter and specific due to the custom flourescence resonance energy transfer (FRET) or fluorogenic substrates used. REF does not require recombinant strains, ensuring normal host-pathogen interactions. We describe the imaging of M. tuberculosis infection using a FRET substrate with maximal emission at 800 nm. The wavelength of the substrate allows sensitive deep tissue imaging in mammals. We will outline aerosol infection of mice with M. tuberculosis, anesthesia of mice, administration of the REF substrate, and optical imaging. This method has been successfully applied to evaluating host-pathogen interactions and efficacy of antibiotics targeting M. tuberculosis.

Imaging Mycobacterium tuberculosis in Mice with Reporter Enzyme Fluorescence

We describe the optical imaging of mice infected with Mycobacterium tuberculosis (M. tuberculosis) using reporter enzyme fluorescence (REF). This protocol facilitates the sensitive and specific detection of M. tuberculosis in pre-clinical animal models for pathogenesis, therapeutics and vaccine research.

Reporter enzyme fluorescence (REF) utilizes substrates that are specific for enzymes present in target organisms of interest for imaging or detection by ...