An investigation of the antimicrobial impact of drug combinations against Mycobacterium tuberculosis strains

Aim: To investigate the in vitro activity of linezolid and ofloxacin in combination with first-line antituberculosis agents (isoniazid and rifampicin) against M. tuberculosis strains. The use of combinations that include fluoroquinolones and oxazolidinone is now being considered for the treatment of resistant Mycobacterium tuberculosis strains. Materials and methods: The minimum inhibitory concentrations of the test drugs were determined by the standard agar dilution method. The interaction of drug combinations was investigated by time-kill method. Results: A total of 9 M. tuberculosis strains were used in this study, 5 of which were multidrug-resistant (MDR) and 4 of which were not. The studied 2-agent drug combinations were indifferent in 4 MDR and 2 non-MDR M. tuberculosis strains, respectively. Additive interaction was observed between isoniazid and ofloxacin in one MDR M. tuberculosis strain on the eighth day and in one non-MDR strain on the third, fifth, and eighth days, respectively, while rifampicin and linezolid exhibited additive interaction in another non-MDR strain on the eighth day. Conclusion: Although many previous studies have found a synergistic activity with similar drug combinations, only additive interaction was observed in some of the M. tuberculosis strains involved in this study.