Name: demonstrating a multi-drug resistant mycobacterium tuberculosis amplification microarray
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This work was supported by the National Institutes of Health (NIH) under grant RC3 AI089106.
MDR-TB nucleic acids were provided by the United Nations Children&#39;s Fund/United Nations Development Programme/World Bank/World Health Organization Special Programme for Research and Training in Tropical Diseases (TDR), Geneva, Switzerland.
We thank Dr. Tom Shinnick of the U.S. Centers for Disease Control and Prevention for guidance on the specific genes and mutations to include in the prototype assay.

For laboratories that follow universal PCR precautions, it is operationally more efficient to include several amplification microarrays and gaskets per substrate and wash all amplification microarrays simultaneously in a bulk container, as described here. Consumable formats are available for performing post-amplification microarray washing steps in an entirely sealed, closed amplicon test, as reported elsewhere30,33.
1. Setup
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	<li>Extract and purify nucleic acids from the sam...

<ol>
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Infect. Dis. 49, 89-97 (2004).</li><li>Yue, J., Shi, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+rifampin-resistant+Mycobacterium+tuberculosis+strains+by+using+a+specialized+oligonucleotide+microarray.">Detection of rifampin-resistant Mycobacterium tuberculosis strains by using a specialized oligonucleotide microarray.</a> Diagn. Microbiol. Infect. Dis. 48, 47-54 (2004).</li><li>Kim, S. Y., Park, Y. 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The extent of multiplexing with an amplification microarray is ultimately dictated by the efficiency of multiplex asymmetric PCR, not the microarray. In our experience, 10-12 unique primer pairs can be readily multiplexed in an amplification microarray format. Conventional primer and probe design criteria therefore apply to new assays, except that one also needs to consider potential interactions between solution-phase nucleic acids and immobilized microarray probes, the thermal efficiency of the thermal cycler, and prob...

Early case detection and rapid treatment are considered the most effective control strategies to reduce Mycobacterium tuberculosis (MTB) transmission1, and there is now a broad consensus in the TB community that a point of care (POC) or near POC test to simultaneously diagnose TB and drug resistance (DR) is needed. Technologies such as Cepheid&#8217;s GeneXpert&#160;and other nucleic acid amplification tests reduce the time to diagnosis for many TB patients, and provide a rapid read-out indicating resistance to rifampin or selected mutations conferring resistance to other first or second line drugs2. Although real-time and isothermal nucleic acid amplification tests are designed to identify the drug resistance mutations that lead to MDR-TB, the spectrum of mutations they detect is often inadequate to design an individualized drug regimen corresponding to the drug resistance profile of the patient, and technical constraints related to optical cross-talk or the complexity of amplification and reporting chemistries3-7 may limit the number of loci or mutations that are detected. Thus, detection technologies with higher multiplexing capacity are required to address known gaps in MDR-TB POC diagnostics.
Microarrays and the WHO-endorsed Hain line probe assays can address the &#8220;multiple gene, multiple mutations&#8221; challenge of diagnosing MDR-TB8-29. Unfortunately, these hybridization-based, multiplexed detection platforms use multistep, complicated, and open-amplicon protocols that require significant training and proficiency in molecular techniques. The amplification microarray30 was designed to address some of these microarray work-flow and operational concerns. The simplifying fluidic principles are to amplify, hybridize, and detect nucleic acid targets within a single microfluidic chamber. The user introduces the nucleic acid and amplification master mix into a fluidic chamber with a pipette and starts the thermal cycling protocol. For the batch processing method shown here, microarrays are subsequently washed in bulk solution, dried, and imaged. This study demonstrates the functionality of an amplification microarray using an MDR-TB microarray test for rpoB (30 mutations), katG (2 mutations), inhA (4 mutations), rpsL (2 mutations), embB (1 mutation), IS1245, IS6110, and an internal amplification and hybridization control. At least one matched pair of microarray probes (wildtype (WT) and single-nucleotide mutant (MU)) is included for each mutation of interest. Purified nucleic acids from multi-drug resistant M. tuberculosis are from the TDR Tuberculosis Strain Bank31. Gel element microarrays are manufactured on glass substrates by copolymerization essentially as described elsewhere32, except that we use 4% monomer and 0.05 mM each probe in the polymerization mixture. Arrays are surrounded with a 50 ml gasket prior to use. After thermal cycling, hybridization, and wash steps, amplification microarrays are imaged on an Akonni portable analyzer. Background-corrected, integrated signal intensities are obtained from the raw .tif images using a fixed circle algorithm. Noise for each gel element is calculated as three times the standard deviation of the local spot backgrounds. Gene targets are typically considered detectable for signal to noise ratio (SNR) values &#8805;3. In order to determine the presence or absence of a specific mutation in each gene or codon, a discriminant ratio is calculated from the SNR values as (WT-MU)/(WT+MU). Discriminant ratios &#60;0 are indicative of a drug-resistance mutation at the locus, whereas ratios &#62;0 are indicative of the wild-type sequence.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;">MDR-TB amplification microarrays, with applied gasket and pre-cut cover slips</td>
			<td>Akonni Biosystems</td>
			<td>Inquire</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Multiplex PCR kit, containing 2X PCR buffer with HotStar Taq plus</td>
			<td>Qiagen</td>
			<td>#206143</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Taq polymerase</td>
			<td>Qiagen</td>
			<td>#201207</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">RNAse-free water</td>
			<td>Qiagen</td>
			<td>#206143&#160;</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Formamide</td>
			<td>Thermo Fisher Scientific, Inc.</td>
			<td>#BP227-500</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">20 mg mL-1 non-acetlyated bovine serum albumin (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>#3B6917</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">5X concentrated MDR-TB primer mix</td>
			<td>Akonni Biosystems</td>
			<td>Inquire</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">500 fg uL-1 amplification and inhibition control</td>
			<td>Akonni Biosystems</td>
			<td>Inquire</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">20X SSPE</td>
			<td>Thermo Fisher Scientific, Inc.</td>
			<td>#BP1328-4</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Triton X-100</td>
			<td>Thermo Fisher Scientific, Inc.</td>
			<td>#BP151-500</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Disinfecting Spray&#160;</td>
			<td>Current Technologies, Inc.</td>
			<td>#BRSPRAY128</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">70% Isopropyl Alcohol</td>
			<td>Decon Labs, Inc.</td>
			<td>#8416</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Equipment</td>
			<td>Company&#160;</td>
			<td>Catalog Number&#160;</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Microarray imager, with automated image and data analysis software</td>
			<td>Akonni Biosystems</td>
			<td>100-20011</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Thermal cycler with flat block insert</td>
			<td>Akonni Biosystems</td>
			<td>100-10021</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">High-throughput wash station and slide holder</td>
			<td>ArrayIt</td>
			<td>HTW</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Dissecting forceps</td>
			<td>Thermo Fisher Scientific, Inc.</td>
			<td>#10-300</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Mini Vortexer</td>
			<td>VWR</td>
			<td>#3365040</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Mini-centrifuge</td>
			<td>VWR</td>
			<td>#93000-196</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">Airbrush Compressor Kit</td>
			<td>Central Pneumatic</td>
			<td>#95630</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Qualitative image analysis can provide insight into sources of experimental noise or variability that are challenging to identify in data tables generated by automated image analysis software. Thus, it can be useful to visually ascertain that 1) all gel elements are intact and undamaged, 2) the global background is free from fluorescent artifacts that might affect individual signal to noise ratio (SNR) values, 3) there is no evidence for bubble formation or nonuniform amplification/hybridization across the array, and 4) ...

Watch this Scientific Journal Video about Demonstrating a Multi-drug Resistant Mycobacterium tuberculosis Amplification Microarray at JoVE.com

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.

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 ...

Research

JoVE Journal

Immunology and Infection

Antimicrobial Susceptibility Testing of Mycobacterium Tuberculosis Complex for First and Second Line Drugs by Broth Dilution in a Microtiter Plate Format

The rapid detection of antimicrobial resistance is important in the effort to control the increase in resistant Mycobacterium 
tuberculosis (Mtb). ...

Sample Preparation of Mycobacterium tuberculosis Extracts for Nuclear Magnetic Resonance Metabolomic Studies

Sample Preparation of Mycobacterium tuberculosis Extracts for Nuclear Magnetic Resonance Metabolomic Studies

Mycobacterium tuberculosis is a major cause of mortality in human beings on a global scale. The emergence of both multi- (MDR) and extensively-(XDR) ...

Growth of Mycobacterium tuberculosis Biofilms

Growth of Mycobacterium tuberculosis Biofilms

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

Protein Misfolding Cyclic Amplification of Prions

Prions  are infectious agents that cause the inevitably fatal transmissible spongiform  encephalopathy (TSE) in animals and humans9,18. The prion protein ...

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

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 ...

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

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 ...

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

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 ...

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

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 ...

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

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 ...

Analysis of 18FDG PET/CT Imaging as a Tool for Studying Mycobacterium tuberculosis Infection and Treatment in Non-human Primates

Analysis of 18FDG PET/CT Imaging as a Tool for Studying Mycobacterium tuberculosis Infection and Treatment in Non-human Primates

Mycobacterium tuberculosis remains the number one infectious agent in the world today. With the emergence of antibiotic resistant strains, new clinically ...