Successful interventions for gram-negative resistance to extended-spectrum beta-lactam antiobiotics.

Antibiotic resistance among nosocomial pathogens in this country's hospitals adds significantly to patient morbidity and mortality, and the cost of health care. Optimism for identifying antimicrobial agents that would "solve the problem" of resistance has been replaced by a much more guarded and realistic view of the battle between humans and pathogenic microorganisms. Efforts now are more appropriately directed toward limiting, rather than completely eliminating, resistance, generally by either infection control or antibiotic control measures, and sometime combinations of the two. Methicillin-oxacillin resistance in Staphylococcus aureus (MRSA) results from the expression of an acquired penicillin-binding protein (PBP 2a) that is not transferable in vitro. In most hospitals, even those with high percentages of MRSA, relatively few resistant clones are identified, suggesting transmission of individual strains throughout the hospital population. Because person-to-person spread is so important in transmission of MRSA, strategies aimed at preventing transmission of the resistant strains are remarkably effective when strictly enforced. Ceftazidime resistance in Enterobacteriaceae results from point mutations within genes that encode widely prevalent and often transferable plasmid-mediated enzymes. In addition, mutations of these genes that allow hydrolysis of cephalosporins usually result in decreased activity against other drugs, including the penicillins and beta-lactamase inhibitors. Effective measures to control ceftazidime-resistant Enterobacteriaceae have as their cornerstone limiting administration of antibiotics that select for the emergence and spread of these mutations, especially ceftazidime. The importance of infection-control techniques in limiting the prevalence of ceftazidime-resistant Enterobacteriaceae is less well established. Methods that are informed by a detailed understanding of the molecular mechanisms of resistance and resistance spread offer the best hope for limiting dissemination of antibiotic-resistant bacteria in a cost-effective manner.