title: Exposure of Staphylococcus aureus to subinhibitory concentrations of β-lactam antibiotics induces heterogeneous vancomycin-intermediate Staphylococcus aureus.
abstract: Glycopeptides are known to select for heterogeneous vancomycin-intermediate Staphylococcus aureus (h-VISA) from susceptible strains. In certain clinical situations, h-VISA strains have been isolated from patients without previous exposure to glycopeptides, such as cystic fibrosis patients, who frequently receive repeated treatments with beta-lactam antibiotics. Our objective was to determine whether prolonged exposure to beta-lactam antibiotics can induce h-VISA. We exposed 3 clinical vancomycin-susceptible methicillin-resistant Staphylococcus aureus (MRSA) strains to ceftazidime, ceftriaxone, imipenem, and vancomycin (as a control) at subinhibitory concentrations for 18 days in vitro. Population analyses showed progressive increases in vancomycin resistance; seven of the 12 derived strains obtained after induction were classified as h-VISA according to the following criteria: area under the curve (AUC) on day 18/AUC of Mu3 of ≥90% and/or growth on brain heart infusion (BHI) agar with 4 mg/liter vancomycin. The derived isolates had thickened cell walls proportional to the level of glycopeptide resistance. Genes known to be associated with glycopeptide resistance (vraSR, yvqF, SA1703, graRS, walKR, and rpoB) were PCR sequenced; no de novo mutations were observed upon beta-lactam exposure. To determine whether trfA, a gene encoding a glycopeptide resistance factor, was essential in the selection of h-VISA upon beta-lactam pressure, a trfA-knockout strain was generated by allelic replacement. Indeed, beta-lactam exposure of this mutated strain showed no capacity to induce vancomycin resistance. In conclusion, these results showed that beta-lactam antibiotics at subinhibitory concentrations can induce intermediate vancomycin resistance in vitro. This induction required an intact trfA locus. Our results suggest that prior use of beta-lactam antibiotics can compromise vancomycin efficacy in the treatment of MRSA infections.
authors: International Center for Infectiology Research, Université de Lyon, Lyon, France INSERM U1111, Lyon, France Ecole Normale Supérieure de Lyon, Lyon, France Université Lyon 1, Lyon, France CNRS, UMR5308, Lyon, France Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Mélanie
authors: M
authors: Roch
authors: Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Perrine
authors: P
authors: Clair
authors: Service of Infectious Diseases, Geneva University Hospitals, Geneva, Switzerland.
authors: Adriana
authors: A
authors: Renzoni
authors: Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Marie-Elisabeth
authors: ME
authors: Reverdy
authors: International Center for Infectiology Research, Université de Lyon, Lyon, France INSERM U1111, Lyon, France Ecole Normale Supérieure de Lyon, Lyon, France Université Lyon 1, Lyon, France CNRS, UMR5308, Lyon, France Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Olivier
authors: O
authors: Dauwalder
authors: International Center for Infectiology Research, Université de Lyon, Lyon, France INSERM U1111, Lyon, France Ecole Normale Supérieure de Lyon, Lyon, France Université Lyon 1, Lyon, France CNRS, UMR5308, Lyon, France Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Michèle
authors: M
authors: Bes
authors: Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Annie
authors: A
authors: Martra
authors: Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Anne-Marie
authors: AM
authors: Freydière
authors: International Center for Infectiology Research, Université de Lyon, Lyon, France INSERM U1111, Lyon, France Ecole Normale Supérieure de Lyon, Lyon, France Université Lyon 1, Lyon, France CNRS, UMR5308, Lyon, France Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Frédéric
authors: F
authors: Laurent
authors: Hospices Civils de Lyon, Centre de Référence Mucoviscidose, Lyon, France.
authors: Philippe
authors: P
authors: Reix
authors: International Center for Infectiology Research, Université de Lyon, Lyon, France INSERM U1111, Lyon, France Ecole Normale Supérieure de Lyon, Lyon, France Université Lyon 1, Lyon, France CNRS, UMR5308, Lyon, France Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France.
authors: Oana
authors: O
authors: Dumitrescu
authors: International Center for Infectiology Research, Université de Lyon, Lyon, France INSERM U1111, Lyon, France Ecole Normale Supérieure de Lyon, Lyon, France Université Lyon 1, Lyon, France CNRS, UMR5308, Lyon, France Hospices Civils de Lyon, Centre National de Référence des Staphylocoques, Lyon, France francois.vandenesch@univ-lyon1.fr.
authors: François
authors: F
authors: Vandenesch
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002442:Ceftazidime / Q000008:administration & dosage / Q000494:pharmacology; D002443:Ceftriaxone / Q000008:administration & dosage / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D015378:Imipenem / Q000008:administration & dosage / Q000494:pharmacology; D016106:Methicillin Resistance / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D046529:Microscopy, Electron, Transmission; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000648:ultrastructure; D014640:Vancomycin / Q000008:administration & dosage / Q000494:pharmacology; D020713:Vancomycin Resistance / Q000187:drug effects*; D047090:beta-Lactams / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D014640:Vancomycin; D015378:Imipenem; D002443:Ceftriaxone; D002442:Ceftazidime