title: Acquired resistance of Nocardia brasiliensis to clavulanic acid related to a change in beta-lactamase following therapy with amoxicillin-clavulanic acid.
abstract: Previous studies have demonstrated that Nocardia brasiliensis is susceptible to amoxicillin-clavulanic acid and that its beta-lactamases are inhibited in vitro by clavulanic acid. A cardiac transplant patient with disseminated infection caused by N. brasiliensis was treated with this drug combination with good response, but relapsed while still on therapy. The relapse isolate was found to be identical to the initial isolate by using genomic DNA restriction fragment patterns obtained by pulsed field gel electrophoresis, but it was resistant to amoxicillin-clavulanic acid. On isoelectric focusing, the beta-lactamase from the relapse isolate exhibited a shift in the isoelectric point (pI) of its major band from 5.10 to 5.04 compared with the enzyme from the pretreatment isolate. As determined by using values of the amount of beta-lactamase inhibitor necessary to give 50 +/- 5% inhibition of beta-lactamase-mediated hydrolysis of 50 microM nitrocefin, the beta-lactamase of the relapse isolate was also 200-fold more resistant than the enzyme from the pretreatment isolate to clavulanic acid and was more resistant to sulbactam, tazobactam, cloxacillin, and imipenem. The beta-lactamase of the relapse isolate exhibited a 10-fold decrease in hydrolytic activity for cephaloridine and other hydrolyzable cephalosporins compared with that for nitrocefin. Acquired resistance to amoxicillin-clavulanic acid in this isolate of N. brasiliensis appears to have resulted from a mutational change affecting the inhibitor and active site(s) in the beta-lactamase.
authors.affiliation: Department of Microbiology, University of Texas Health Center, Tyler 75710.
authors.forename: V A
authors.initials: VA
authors.lastname: Steingrube
authors.forename: R J
authors.initials: RJ
authors.lastname: Wallace
authors.forename: B A
authors.initials: BA
authors.lastname: Brown
authors.forename: Y
authors.initials: Y
authors.lastname: Pang
authors.forename: B
authors.initials: B
authors.lastname: Zeluff
authors.forename: L C
authors.initials: LC
authors.lastname: Steele
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000658:Amoxicillin / Q000627:therapeutic use*; D019980:Amoxicillin-Potassium Clavulanate Combination; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D019818:Clavulanic Acid; D002969:Clavulanic Acids / Q000494:pharmacology* / Q000627:therapeutic use*; D004352:Drug Resistance, Microbial; D004359:Drug Therapy, Combination / Q000627:therapeutic use; D006801:Humans; D007525:Isoelectric Focusing; D008826:Microbial Sensitivity Tests; D009615:Nocardia / Q000187:drug effects* / Q000201:enzymology; D009617:Nocardia Infections / Q000188:drug therapy* / Q000378:metabolism; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002969:Clavulanic Acids; D065093:beta-Lactamase Inhibitors; D019818:Clavulanic Acid; D019980:Amoxicillin-Potassium Clavulanate Combination; D000658:Amoxicillin; D001618:beta-Lactamases