Mechanisms and clinical significance of resistance to new beta-lactam antibiotics.

The newer beta-lactam antibiotics, including various ureidopenicillins, second- and third-generation cephalosporins, carbapenems and monobactams, are active against many bacteria that are resistant to older penicillins, such as ampicillin and ticarcillin. Nonetheless, resistance to the newer agents can arise, and in this article the mechanisms whereby it does so are reviewed and their clinical significance is discussed.