title: Mupirocin-induced mutations in ileS in various genetic backgrounds of methicillin-resistant Staphylococcus aureus.
abstract: Topical mupirocin is widely used for the decolonization of methicillin-resistant Staphylococcus aureus (MRSA) carriers. We evaluated the capacity of various MRSA clonotypes to develop mutations in the ileS gene associated with low-level mupirocin resistance. Twenty-four mupirocin-sensitive MRSA isolates from a variety of genotypes (determined by a multilocus variable-number tandem-repeat assay) were selected. Mupirocin MICs were determined by Etest. The isolates were then incubated in subinhibitory concentrations of mupirocin for 7 to 14 days. Repeat MIC determinations and sequencing of the ileS gene were then performed. Doubling times of isolates exposed to mupirocin and of unexposed isolates were compared. We found that exposure to mupirocin led to rapid induction of low-level resistance (MICs of 8 to 24 μg/ml) in 11 of 24 (46%) MRSA isolates. This phenomenon was observed in strains with diverse genetic backgrounds. Various mutations were detected in 18 of 24 (75%) MRSA isolates. Acquisition of mutations appeared to be a stepwise process during prolonged incubation with the drug. Among the five isolates exhibiting low-level resistance and the highest MICs, four tested sensitive after incubation in the absence of mupirocin but there was no reversion to the susceptible wild-type primary sequence. Resistance was not associated with significant fitness cost, suggesting that MRSA strains with low-level mupirocin resistance may have a selective advantage in facilities where mupirocin is commonly used. Our findings emphasize the importance of the judicious use of this topical agent and the need to closely monitor for the emergence of resistance.
authors.affiliation: Infection Control Programme, Department of Internal Medicine, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland Departments of Infectious Diseases and Microbiology, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Andie S
authors.initials: AS
authors.lastname: Lee
authors.affiliation: Genomic Research Laboratory, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Yann
authors.initials: Y
authors.lastname: Gizard
authors.affiliation: Department of Epidemiology and Clinical Microbiology, National Medicines Institute, Warsaw, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Empel
authors.affiliation: Genomic Research Laboratory, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Eve-Julie
authors.initials: EJ
authors.lastname: Bonetti
authors.affiliation: Infection Control Programme, Department of Internal Medicine, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Stephan
authors.initials: S
authors.lastname: Harbarth
authors.affiliation: Genomic Research Laboratory, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland patrice.francois@genomic.ch.
authors.forename: Patrice
authors.initials: P
authors.lastname: François
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D006801:Humans; D007533:Isoleucine-tRNA Ligase / Q000235:genetics*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D016712:Mupirocin / Q000494:pharmacology*; D020125:Mutation, Missense; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D016712:Mupirocin; D007533:Isoleucine-tRNA Ligase