EVALUATION OF VARIOUS BIPHASIC MEDIA FOR ISOLATION OF MYCOBACTERIA FROM SPUTUM SAMPLES IN A TERTIARY CARE HOSPITAL

BACKGROUND: Mycobacterial culture and identification provide a definitive diagnosis of tuberculosis. Culture on Lowenstein-Jensen medium (LJ) is delayed because of the slow growth of Mycobacterium tuberculosis (MTB) on LJ. Automated liquid culture systems are expensive. For early, efficient and inexpensive detection of MTB, various isolation methods have been devised. We evaluated various biphasic media in comparison to LJ. OBJECTIVES: Evaluation of LJ with Middlebrook 7H9 (MB7H9), LJ with MB7H9 and TTC (2, 3,5-Triphenyl-tetrazolium chloride), MB7H10 with MB7H9, MB7H10 with MB7H9 and TTC in comparison to LJ as the gold standard in terms of diagnostic accuracy, turnaround time (TAT), rate of contamination, feasibility and ease of performance. STUDY DESIGN: Comparative cross sectional study. PARTICIPANTS: 244 respiratory samples. METHODS: The media were inoculated with decontaminated samples, incubated at 37oC and observed alternatively for 8 weeks for any visible growth/colour change. The number of days to positivity/contamination was recorded. RESULTS: All the media showed similar sensitivities (65% for LJ with MB7H9, 68.33% for both MB7H10 with MB7H9 and MB7H10 with MB7H9 and TTC) except LJ with MB7H9 medium (35%). Highest specificity was observed for LJ with MB7H9 medium (94.02%), followed by LJ with MB7H9 and TTC (91.30 %), MB7H10 with MB7H9 (80.44%) and MB7H10 with MB7H9 and TTC (79.35%). Highest diagnostic accuracy was observed for LJ with MB7H9 and TTC (85%) followed by LJ with MB7H9 (80%). The lowest mean TAT was 12.9 days for MB7H10 with MB7H9 and TTC followed by 15.8 days for MB7H10 with MB7H9 and 25.14 days for LJ. The contamination rate was higher for MB7H10 with M7H9 and TTC (4.92%) compared to other media (1.6%-4.1%) CONCLUSIONS: Use of Middlebrook containing biphasic media was found to be highly acceptable in terms of cost, diagnostic accuracy, TAT, contamination rate, ease of laboratory work and feasibility. IMPLICATIONS: These media with their good accuracy and ease of performance can be used as an adjunct to conventional LJ medium in routine mycobacteriology laboratory.