Antibiotic Susceptibility of Multi-drug resistant Mycobacterium tuberculosis using Flow Cytometry

Increased resistance of Mycobacterium tuberculosis (M. tuberculosis) to antibiotics has emphasized the need for rapid susceptibility testing. BACTEC MGIT 960 system is routinely used for drug susceptibility testing; however, the main drawback is the long incubation time. An alternative flow cytometry-based assay was evaluated for the assessment of drug susceptibility. Thirteen multi-drug resistant (MDR) M. tuberculosis cultures were tested against rifampicin (1 μg/ml), isoniazid (0.2 μg/ml), ethambutol (7.5 μg/ml), and ofloxacin (2 μg/ml) using flow cytometry by staining cells with SYTO16 and propidium iodide. Correlation rates of flow cytometry results with BACTEC MGIT 960 system were 28.5% (rifampicin); 15.4% (isoniazid), 61.5% (ethambutol) and 46.1% (ofloxacin). Findings indicate that while flow cytometry for tuberculosis (TB) drug susceptibility may reduce the length of time taken for diagnosis, there was low correlation with BACTEC MGIT 960. The high cost associated with implementation of the technique in diagnostic laboratories is a further disadvantage. Further studies with larger sample sizes are needed to confirm these data.