EMERGENCE OF ANTIMICROBIAL RESISTANCE IN GRAM-NEGATIVE BACILLI CAUSING BACTEREMIA DURING THERAPY

Treatment of serious infections caused by gram-negative bacilli with b eta-lactam antimicrobial agents can induce Class I beta-lactamase prod uction. This phenomenon can result in resistant microorganisms, and ha s been postulated to be a cause of therapeutic failure. The charts of patients bacteremic with Pseudomonas aeruginosa, Serratia marcescens, Enterobacter cloacae, Citrobacter freundii, Proteus vulgaris, and Prov idencia species (n=120) during a 3-year period were reviewed to determ ine how common the emergence of resistance was, and to determine if in vitro susceptibility testing was a reliable therapeutic guide. Emerge nce of resistance was believed to occur when a subsequent bacteremic i solate showed at least a fourfold increase in minimum inhibitory conce ntration accompanied by a change of interpretive susceptibility catego ry. In the group of patients who survived at least 48 hours that recei ved beta-lactam therapy (n=76), one case of emergence of resistance wa s identified (1.3%). Emergence of resistance to beta-lactam antimicrob ial agents did not commonly cause therapeutic failure at our instituti on, and susceptibility testing of gram-negative bacilli by usual metho ds was a reliable guide to antimicrobial therapy.