In a high tuberculosis burdened country like India, rapid, cost-effective, and reliable diagnostic tools for tuberculosis are an urgent need of the hour to prevent inappropriate treatment strategies and further spread of resistance. This study aimed to estimate the proportion of new smear-positive tuberculosis cases with primary resistance to rifampicin and/or isoniazid as well as identify the common mutations associated with it. Sputum of 200 newly diagnosed smear-positive cases of 1+ score and above was directly subjected to Line Probe Assay using the GenoType MTBDRplus assay kit. All samples were inoculated onto solid media and 61 samples were inoculated in automated liquid culture also. The Line Probe Assay gave hundred percent interpretable results with 2.5% of the study population showing resistant pattern. Only 1% of the cases were primary multidrug resistant tuberculosis and 1.5% showed isoniazid monoresistance. S531L and C15T were the most common genetic mutations seen for rifampicin and isoniazid resistance, respectively. 40% had absent rpoB wild type 8 band indicating probable silent mutation after clinical correlation. The average turnaround time for Line Probe Assay was far less (3.8 days) as compared to solid and liquid cultures (35.6 days and 13.5 days, resp.).

Introduction:The identification of smear negative pulmonary and extrapulmonary tuberculosis continues to remain a diagnostic challenge. This study was conducted in a tertiary care setup in north Kerala to isolate and identify mycobacteria by culture from radiologically and clinically suspected cases of smear negative pulmonary and extrapulmonary tuberculosis.Methods:A total of 200 samples (100 pulmonary and 100 extrapulmonary) were processed and cultured by automated (MB/BacT) and conventional methods. Heat stable catalase test, nitrate reduction test and detection of MPT 64 antigen were done to aid species identification.Results:Overall culture positivity was 7% (14 isolates - 8 pulmonary and 6 extrapulmonary) of which 92.9% (13) of the isolates were Mycobacterium tuberculosis and 7.1% (1) was Mycobacterium fortuitum (identified by molecular typing). Detection rate by automated method was 7% (14) and by conventional method was only 1.5% (3).Conclusion:Despite its shortcomings and low positivity, culture still remains the gold standard for the diagnosis of EPTB and SNPT. However, automated liquid cultures have better isolation rates than the conventional LJ culture. Subjecting these isolates to rapid diagnostic tests like antigen detection and LPA can aid in the early institution of appropriate treatment regimen.