Evaluation of a microcolony detection method and phage assay for rapid detection of Mycobacterium tuberculosis in...

Early and rapid diagnosis of tuberculosis is necessary for both treatment and control of the disease. This study evaluated two microcolony observation techniques based on liquid and solid media and a mycobacteriophage assay, to evaluate their effectiveness in the diagnosis of pulmonary TB compared with a standard culture (BACTEC 460 and LJ medium). Middlebrook7H9 (M7H9) broth based on microcolony determination detected 57/61 positives cultures (n = 200) with a sensitivity of 93.4% and a specificity of 87.1%. M7H11 agar detected 57/62 positive cultures (n = 198) with a sensitivity of 91.9% and a specificity of 89.7%. The mycobacteriophage assay detected 98/143 (68.5%) of positive samples. The time to positivity was 48 hours in the mycobacteriophage assay versus 7 days in both the M7H9 broth and M7H11 agar. The costs in comparison with the culture (BACTEC 460 and LJ) were 33% and 48% for the microcolony and mycobacteriophage methods, respectively. Microcolony methods were rapid and cost effective compared to standard cultures. The mycobacteriophage assay, despite its lower sensitivity, has a short turn around time, and may be recommended as a screening test in countries with a low prevalence of tuberculosis.