Effect of five irreversible inhibitors on beta-lactamase from Shigella flexneri UCSF-129.

: The effect of five irreversible inhibitors on purified enzyme from Shigella flexneri USCF-129 and also in vitro, was investigated. The I50 was 0.091, 0.30, 0.40 and 0.87 microgram/ml for 6 beta-iodopenicillanic, clavulanic, olivanic and 6 beta-bromopenicillanic acids, respectively, and 255 micrograms/ml for sulbactam. The synergic responses of these inhibitors (10 micrograms/ml) were studied with ampicillin and cephradin on S. flexneri. The MIC of ampicillin was reduced by 128 times using 6 beta-iodopenicillanic, 6 beta-bromopenicillanic and clavulanic acids. This indicates that the beta-lactamase of S. flexneri is a penicillinase. Since these inhibitors have a strong action against the beta-lactamase and last for at least 6 h, further work is expected to reveal their medical value.