In vitro evaluation of linezolid and meropenem against clinical isolates of multi drug resistant tuberculosis by mycobacterial growth indicator tube [MGIT] 960

ABSTRACT

To evaluate the in vitro effectiveness of multiple breakpoint concentrations of newer antituberculosis agents [Linezolid and Meropenem] against Multi Drug-Resistant Tuberculosis [MDR-TB] isolates. A descriptive cross-sectional study. Microbiology Department, Armed Forces Institute of Pathology [AFIP], Rawalpindi, from September 2011 to August 2013. A total of 100 MDR-TB isolates recovered during the study period were subjected to susceptibility testing against multiple breakpoint concentrations of Linezolid [LZD] and Meropenem [MER]. The breakpoint concentration used for LZD were 0.5, 1.0 and 2.0 microg/ml, while for MER were 4.0, 8.0 and 16 microg/ml. Mycobacterial Growth Indicator Tube [MGIT] 960 system was used to carry out drug susceptibility testing as per recommended protocol. At break point concentration of 0.5 microg/ml, 80 out of 100 [80%] MDR-TB isolates were susceptible to LZD while at breakpoint concentration of 1.0 microg/ml and 2.0 microg/ml, 96/100, [96%] of MDR-TB isolates were susceptible. For MER, at breakpoint concentrations of 4.0 microg/ml no MDR-TB isolate was susceptible, while at 8.0 microg/ml 3/100, [3%] and at 16.0 microg/ml 11/100, [11%] of MDR-TB isolates were susceptible. LZD was found to have excellent in vitro efficacy as 96% of MDR-TB isolates were susceptible at breakpoint concentration of 1.0 microg/ml or more. In case of MER it was found that in vitro susceptibility improved as the break point concentrations were increased