[Evaluation of Tetrazolium Violet and Resazurin Assays for Ciprofloxacin Susceptibility Testing of Resistant Mycobacterium tuberculosis Isolates].

Tuberculosis, caused by Mycobacterium tuberculosis, is still a serious public health concern. Antimycobacterial drug resistance which is in an increasing trend worldwide aids to the importance of tuberculosis problem. Fluoroquinolones which exhibit in vitro and in vivo anti-mycobacterial activity, are being recommended by World Health Organization as alternative drugs particularly for the treatment of multidrug resistant tuberculosis. Rapid detection of antimycobacterial resistance is of great importance for the effective treatment of patients with tuberculosis. In this study, we evaluated the efficiency of tetrazolium violet (TV) and resazurin (RES) assays in terms of rapid detection of bacterial growth and ciprofloxacin resistance in M.tuberculosis clinical isolates. Thirty M.tuberculosis isolates which were resistant to at least one of the first-line anti-tuberculosis drugs were tested using TV and RES assays in addition to gold standard agar proportion test. Standard strain M.tuberculosis H37Ra was also included in each run. The tests were performed in four sets as TV and RES were added on day 5, 7, 10 and 12. For the TV assay, any change in colour from yellow to dark purple was recorded as bacterial growth. For the RES assay, any change in colour from blue to pink was recorded as bacterial growth. The optimal incubation period for detection of growth and resistance was 7 days for 25 of 30 bacteria. However, results for five isolates with low inoculum rates were detected on 10th and 12th days. Any change in colour in drug containing media was recorded as resistance to ciprofloxacin. All the susceptibility results were consistent with those obtained from agar proportion method. As indicated by our results, TV and RES assays are rapid and simple tests which could be used for detection of bacterial growth and ciprofloxacin resistance in M.tuberculosis clinical isolates. Widespread use of such colorimetric tests will help to minimize the need of sophisticated expensive susceptibilty test systems particularly in low income countries.