# Detecting heteroresistant M. tuberculosis infections using SuperSelective PCR

> **NIH NIH R21** · RBHS-NEW JERSEY MEDICAL SCHOOL · 2020 · $196,250

## Abstract

PROJECT SUMMARY
A primary objective of tuberculosis (TB) treatment is to prevent the emergence of drug-resistant disease.
Standardized treatment regimens that include isoniazid, rifampin, pyrazinamide, and ethambutol are the
backbone of the directly observed therapy-short course strategy for global TB control. The emergence of drug
resistance during anti-TB therapy presents a major challenge to these efforts. Treatment of multidrug resistant
TB requires the use of more toxic and less effective second-line drugs, and thus the prevention of emergence of
drug resistance is a key aspect of TB elimination efforts. Our ability to study the development of drug resistance
during M. tuberculosis infection is severely limited by insensitive tools to detect rare drug-resistant mutants in
mixed populations. Conventional drug susceptibility testing using the agar proportion method defines phenotypic
drug resistance at a threshold of 1% colony growth on drug-containing media. Traditionally, heteroresistant TB
has been defined as between 1-99% colony growth on drug-containing media, with 100% defined as full
resistance. Importantly, M. tuberculosis isolates display molecular heteroresistance when mutant M. tuberculosis
DNA- conferring drug resistance- is simultaneously detected alongside wild-type (i.e. drug-susceptible) DNA.
However, a major limitation of conventional polymerase chain reaction (PCR) methodology is the inability to
amplify rare mutant sequences in a background of abundant wild-type DNA. Our long-term goal is to develop a
new tool (“SuperSelective” PCR methods) to detect and monitor heteroresistant M. tuberculosis infections during
the course of treatment. The objectives of this application are to develop and test SuperSelective PCR methods
for the detection of rare mutations in genes encoding isoniazid or rifampin resistance, despite an abundant
background of wild-type M. tuberculosis DNA. This work will directly lead to clinical studies of patient factors that
contribute to the emergence of rare drug-resistant mutants during anti-TB treatment. With this new
understanding, we can direct interventions towards preventing anti-TB drug resistance.

## Key facts

- **NIH application ID:** 9987509
- **Project number:** 5R21AI146820-02
- **Recipient organization:** RBHS-NEW JERSEY MEDICAL SCHOOL
- **Principal Investigator:** Salvatore A.E. Marras
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $196,250
- **Award type:** 5
- **Project period:** 2019-08-01 → 2022-07-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9987509

## Citation

> US National Institutes of Health, RePORTER application 9987509, Detecting heteroresistant M. tuberculosis infections using SuperSelective PCR (5R21AI146820-02). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/9987509. Licensed CC0.

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