In Vitro Evaluation of Linezolid and Meropenem Against Clinical Isolates of Multi Drug Resistant Tuberculosis By Mycobacterial Growth Indicator Tube (MGIT) 960.

OBJECTIVE 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. STUDY DESIGN A descriptive cross-sectional study. PLACE AND DURATION OF STUDY Microbiology Department, Armed Forces Institute of Pathology (AFIP), Rawalpindi, from September 2011 to August 2013. METHODOLOGY 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 µg/ml, while for MER were 4.0, 8.0 and 16 µg/ml. Mycobacterial Growth Indicator Tube (MGIT) 960 system was used to carry out drug susceptibility testing as per recommended protocol. RESULTS At break point concentration of 0.5 µg/ml, 80 out of 100 (80%) MDR-TB isolates were susceptible to LZD while at breakpoint concentration of 1.0 µg/ml and 2.0 µg/ml, 96/100, (96%) of MDR-TB isolates were susceptible. For MER, at breakpoint concentrations of 4.0 µg/ml no MDR-TB isolate was susceptible, while at 8.0 µg/ml 3/100, (3%) and at 16.0 µg/ml 11/100, (11%) of MDR-TB isolates were susceptible. CONCLUSION LZD was found to have excellent in vitro efficacy as 96% of MDR-TB isolates were susceptible at breakpoint concentration of 1.0 µg/ml or more. In case of MER it was found that in vitro susceptibility improved as the break point concentrations were increased.