Evolution and clinical importance of extended-spectrum beta-lactamases.

In the process of evolution, bacteria have acquired well-developed mechanisms of resistance to an extensive array of hostile substances. This time-tempered system of defense is so intricate and adaptable that contemporary medicine has been hard-pressed to maintain an advantage. In this article, the processes responsible for bacterial resistance to extended-spectrum cephalosporins are reviewed. Particular emphasis is placed on the extended-spectrum beta-lactamases that have emerged to provide bacteria with formidable resistance to modern drugs. Avoidance of this problem requires limitations on extended-spectrum cephalosporin usage. While carbapenems are clearly the treatment of choice for infections caused by these pathogens, empirical use of beta-lactam/beta-lactamase inhibitors such as piperacillin/tazobactam has been associated with reduction in the prevalence of cephalosporin resistance.