Rapid detection of Mycobacterium tuberculosis in sputum samples by microscopic observation methods

Background: Rapid diagnosis of pulmonary tuberculosis is essential for treatment as well as control. This study evaluated two microcolony observation techniques based on liquid and solid media, for their effectiveness in the diagnosis of pulmonary TB compared with a standard culture (BACTEC 460 and LJ medium).Results: Middlebrook7H9 (M7H9) broth based on microcolony determination detected 57/61 positives cultures (n=200) with a sensitivity of 93% and a specificity of 87%. M7H11 agar detected 57/62 positive cultures (n=198) with a sensitivity of 92% and a specificity of 90%. These methods were rapid with average time to positivity of 7.8 days as compared to standard cultures (14 days for BACTEC and 25 days for LJ). Both microcolony detection methods were 33% costs effective in comparison with the culture (BACTEC 460 & LJ).The contamination rate was high i.e. 8% and 12% for M7H9 broth and M7H11 agar respectively.Conclusion: Both microcolony methods are rapid and cost effective, therefore can be used along with conventional LJ cultures in laboratories with low to medium workload for rapid presumptive diagnosis. However, both methods need the adjustment/ addition of antibiotics to prevent growth of contaminants.