Analysis of Multi Drug Resistant Mycobacterium tuberculosis Clinical Isolates for Susceptibility to Linezolid and Verapamil using MGIT 960

DOI: 10.21276/sjmps.2018.4.10.17 Abstract: Pakistan stands among the top five highest tuberculosis burden countries. Emergence of multi drug resistant Mycobacterium tuberculosis limited the spectrum of drugs of choice to treat tuberculosis. Among several, the activation of efflux pumps is one of mechanisms that mediate drug resistance in M. tuberculosis. Here, we tested efflux pump inhibitor verapamil and third line tuberculosis drug linezolid for antimicrobial activity against locally isolated multi drug resistant M. tuberculosis isolates using MGIT 960. M. tuberculosis isolates were collected from two tertiary care hospitals based in Lahore. Out of 100 isolates, 56 % (n=56) were found to be multi drug resistant (MDR). Out of MDR-TB, 5.36% (n=3) were additionally resistant to linezolid and 41.07% (n=17) were resistant to amikacin. One moxifloxacin resistant isolate was identified. In linezolid resistant strains, rplC gene was sequenced where rplC T640C mutation was identified in two of three linezolid resistant strains. The minimum inhibitory concentration of verapamil in 84.5% isolates was 256 μg/ml and the growth of remaining 16.5% isolates was inhibited by verapamil at the concentration of 512 μg/ml. Assessment of synergism between verapamil and other drugs including rifampicin, isoniazid, linezolid, amikacin and moxifloxacin revealed that verapamil at the concentration of 256 μg/ml inhibited the growth of MDR-TB isolates in presence of respective drugs. Our findings suggest that linezolid resistance have started emerging in local isolates. Further studies are required at higher level to identify the exact mechanism.