In vitro antimicrobial activities of capuramycin analogues against non-tuberculous mycobacteria

Objectives To determine antibacterial activity of capuramycin analogues SQ997, SQ922, SQ641 and RKS2244 against several non-tuberculous mycobacteria (NTM). Methods In vitro antibiotic activities, i.e. MIC, MBC, rate of killing and synergistic interaction with other antibiotics, were evaluated. Results SQ641 was the most active compound against all the NTM species studied. The MIC of SQ641 was ≤0.06–4 mg/L for Mycobacterium avium complex (MAC; n = 20), 0.125–2 mg/L for M. avium paratuberculosis (MAP; n = 9), 0.125–2 mg/L for Mycobacterium kansasii (MKN;n = 2), 0.25–1 mg/L for Mycobacterium abscessus (MAB; n = 11), 4 mg/L for Mycobacterium smegmatis (MSMG; n = 1), and 1 and 8 mg/L for Mycobacterium ulcerans (MUL; n = 1), by microdilution and agar dilution methods, respectively. SQ641 was bactericidal against NTM, with an MBC/MIC ratio of 1 to 32, and killed all mycobacteria faster than positive control drugs for each strain. In chequerboard titrations, SQ641 was synergistic with ethambutol against both MAC and MSMG, and was synergistic with streptomycin and rifabutin against MAB. Conclusions In vitro, SQ641 was the most potent of the capuramycin analogues against all NTM tested, both laboratory and clinical strains.