The influence of beta-lactamases on minimal inhibitory concentrations.

The stability towards hydrolysis by beta-lactamases is commonly used as a major criterion for the quality of a beta-lactam antibiotic. The activity of a beta-lactam compound is influenced by many factors, however. After the introduction of third generation cephalosporins, evidence arose that beta-lactamases can be the only reason for resistance, although the drug is not or only slightly hydrolyzed by the corresponding enzyme. Here it seems as if binding of the antibiotic to the beta-lactamase is the main factor which influences the drug's activity. But, in fact, the situation is much more complicated, as at least several different factors must be considered in combination with beta-lactamase activity.