Timely Detection of Drug-resistant Tuberculosis Using Thin Layer Agar in Nigeria

Background: The global prevalence of drug-resistant tuberculosis poses serious public health challenges which have heightened the need for evaluation and utilization of new tools for the disease diagnosis, especially in developing countries. In order to evaluate the rapidity and accuracy of Thin Layer Agar (TLA) in the diagnosis of drug resistant TB; a comparative study was carried out in Nigeria.

Methods: Concentrated sputum specimens were inoculated onto Lowenstein Jensen (LJ) slopes and quadrant TLA petri-plates containing 0.2 μg/ml of isoniazid, 0.5 μg/ml of rifampicin, 0.5 mg/ml of para-nitrobenzoic acid (PNB), and growth medium without drug served as control. Inoculated TLA plates were sealed, incubated, and examined microscopically at regular intervals for the appearance of microcolonies; and compared with the conventional LJ-proportion method.

Results: The mean time-to–detection of rifampicin-resistant strains of Mycobacterium tuberculosis (MTB) was 13 days and 56 days using TLA and LJ-proportion method respectively. The sensitivity, specificity, overall accuracy, positive and negative predictive values for detection of rifampicin resistance on TLA were 95.2%, 100%, 99.4%, 100% and 99.3% respectively. Using LJ-proportion method as the gold standard, 98.2% of rifampicin-resistant TB was detected on TLA.

Conclusion: TLA method may provide a viable alternative tool for early and accurate detection of TB drug-resistance, and consequent initiation of appropriate treatment for the disease control, particularly at the peripheral level of health services in limited-resource settings.