title: Emergence of resistance in gram-negative bacteria during therapy with expanded-spectrum cephalosporins.
abstract: To assess the clinical importance of emergence of beta-lactam resistance caused by stable derepression of chromosomal beta-lactamases, sequential cultures from patients treated with expanded-spectrum cephalosporins were monitored for the persistence of bacteria possessing these enzymes. Antibiotic susceptibilities and beta-lactamase production before and after cefoxitin induction were determined in sequential isolates of individual bacterial strains. Of 49 strains isolated from 44 patients, 25 strains (51%) were eradicated by cephalosporin therapy, 17 strains (35%) persisted with unchanged susceptibility in sequential cultures, and 7 strains (14%) from 7 patients developed multiple beta-lactam resistance during cephalosporin therapy. In 6 of the 7 strains, resistance was associated with stable derepression of beta-lactamases. In the patient group whose strains developed resistance, subsequent use of non-beta-lactam antibiotics was more frequent and mortality was higher.
mesh_terms: D001424:Bacterial Infections / Q000188:drug therapy* / Q000382:microbiology; D002511:Cephalosporins / Q000494:pharmacology* / Q000627:therapeutic use; D004352:Drug Resistance, Microbial; D004790:Enzyme Induction; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D001618:beta-Lactamases / Q000096:biosynthesis*
chemical_list: D002511:Cephalosporins; D001618:beta-Lactamases