Thin-layer agar (TL7H11) for rapid isolation of <i>Mycobacterium tuberculosis</i> in sputum specimens

Abstract

Background: Tuberculosis (TB) remains one of the major causes of death from a single infectious agent worldwide. The early detection of new cases of pulmonary tuberculosis is an important goal in tuberculosis control program.

Objective: 1n this study, thin layer agar (TLA) culture was compared with Lowenstein-Jensen (LJ) culture for rapid detection of pulmonary tuberculosis.

Methods: It was a cross sectional study conducted in National Tuberculosis Reference Labora­tory (NTRL) of National Institute of Disease of Chest and Hospital (NIDCH), Dhaka, from July 2010 to June 2011. A total of 100 sputum smear positive for acid fast bacilli (AFB) by Z-N staining, pulmonary tuberculosis patients were included in this study. Samples were processed by modified Petroff method and then cultured on thin layer 7H11(TL7H11) plates and L-J tubes. TL7H11 plates were observed microscopically for rnicrocolony growth once a week for 6 weeks, and L-J tubes were observed once a week for 8 weeks.

Results: The recovery rates of mycobacteria on only TLA, only LJ and on both media were 90%, 97% and 88% respectively. Overall positivity was 99% in both L-J and TLA media. Mean time for detection of mycobacteria on TLA was 9.04±1.66 days compared to 21.78±6.19 days on L-J media. The rate of contamination was higher (6%) in L-J media than in TLA media (4%).

Conclusion: The TL7H11 media can be used as an alternative to the Lowenstein-Jensen medium for early isolation of mycobacteria in resource constrained settings.