[Mechanisms of bacterial resistance to beta-lactams by beta-lactamases]

The beta-lactamases are bacterial enzymes that inactivate beta-lactam antibiotics by catalyzing the hydrolysis of the amide group of the beta-lactam ring. They are the source of much bacterial resistance to those antibiotics. Structural studies on the enzymes, i.e., penicillinases and cephalosporinases, are now well-advanced and the up-to-date knowledge of this research field were explained together with the proposed mechanism of beta-lactam hydrolysis by a cephalosporinase. After the introduction of the beta-lactamase-stable beta-lactams such as oxyimino cephalosporins, R plasmid-mediated penicillinases and a chromosomal cephalosporinase have been found to be adapted to the new drugs by mutation. The characteristics of the mutant beta-lactamases and their importance in the bacterial resistance to the new beta-lactams were explained.