Suppression of the growth of six potentially-pathogenic mycobacteria by beta-lactam/beta-lactamase-inhibitors.

Drug-resistant tuberculosis and opportunistic infections by mycobacteria in immunocompromised subjects are not readily controlled with the antimycobacterial drugs now available. beta-Lactam antibiotics, the most widely used antibacterial agents, are ineffective against mycobacteria since they synthesize beta-lactamases. The beta-lactam/beta-lactamase-inhibitor combinations are used at present to treat infections caused by other beta-lactamase-positive organisms. Six potentially-pathogenic mycobacteria: Mycobacterium avium, M. chelonei, M. haemophilum, M. microti, M. scrofulaceum and M. simiae, were cultured in 7H9 medium (containing Tween 80 and albumin, dextrose, catalase) at 37 degrees C for 10-14 days, with or without various concentrations (2-100 micrograms/ml) of ampicillin/sulbactam, amoxicillin/clavulanate and piperacillin/tazobactam. More than 50-80% inhibition of the mycobacterial growth was observed at drug levels of 40-100 micrograms/ml in the medium; the drugs were active even when the detergent (Tween 80) was omitted. Against four of the mycobacteria, ampicillin/sulbactam proved to be the most active. The beta-lactam/beta-lactamase-inhibitor combinations may be of use as rational therapeutic agents against mycobacterial infections.