Evolution and clinical importance of extended-spectrum beta-lactamases

In the process of evolution, bacteria have acquired well-developed mechanis ms of resistance to an extensive array of hostile substances. This time-tem pered system of defense is so intricate and adaptable that contemporary med icine has been hard-pressed to maintain an advantage. In this article, the processes responsible for bacterial resistance to extended-spectrum cephalo sporins are reviewed. Particular emphasis is placed on the extended-spectru m beta -lactamases that have emerged to provide bacteria with formidable re sistance to modern drugs. Avoidance of this problem requires limitations on extended-spectrum cephalosporin usage. While carbapenems are clearly the t reatment 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 resis tance.