In-vitro susceptibility of Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium kansasii to amoxycillin and ticarcillin in combination with clavulanic acid.

The in-vitro susceptibility of Mycobacterium tuberculosis, M. bovis, and M. kansasii to amoxycillin alone and in combination with 2 mg/l of clavulanic acid was evaluated by broth dilution. The MIC90 of amoxycillin plus clavulanic acid was 4 mg/l compared with greater than 32 mg/l for amoxycillin alone when tested against M. tuberculosis (n = 27). M. bovis (n = 8) was the most susceptible species with an MIC90 of amoxycillin 8 mg/l, compared with 0.5 mg/l for the combination. M. kansasii (n = 6), with an MIC90 of 16 mg/l for amoxycillin plus clavulanic acid was more resistant than either M. tuberculosis or M. bovis. Ticarcillin plus clavulanic acid with an MIC90 of 32 mg/l was less active against M. tuberculosis (n = 28) than amoxycillin plus clavulanic acid. The addition of clavulanic acid to amoxycillin greatly improves its in-vitro activity against M. tuberculosis and M. bovis.