No abstract

beta-Lactamases are the principal mechanism of bacterial resistance to beta-lactam antibiotics. In recent years the number and variety of new beta-lactamases detected has risen at an alarming rate, apparently in response to the clinical use of novel classes of beta-lactam antibiotics. This paper reviews the structure and evolution of beta-lactamases in an attempt to understand the pressures that have contributed to their emergence.

Enterococcus faecium strains resistant to ampicillin, high levels of gentamicin, and vancomycin but susceptible to teicoplanin (vanB class vancomycin resistance) were recovered from 37 patients during an outbreak involving a 250-bed university-affiliated hospital. Three isolates with vancomycin MICs ranging from 8 to 256 ,ug/ml all hybridized with a vanB probe. Restriction endonuclease analysis of chromosomal and plasmid DNA suggested that all isolates tested were derived from a single clone. Vancomycin resistance was shown to be transferable. Risk factors for acquiring the epidemic strain included proximity to another case patient (P, 0.0005) and exposure to a nurse who cared for another case patient (P, 0.007). Contamination of the environment by the epidemic strain occurred significantly more often when case patients had diarrhea (P,