title: Altered Competitive Fitness, Antimicrobial Susceptibility, and Cellular Morphology in a Triclosan-Induced Small-Colony Variant of Staphylococcus aureus.
abstract: Staphylococcus aureus can produce small-colony variants (SCVs) that express various phenotypes. While their significance is unclear, SCV propagation may be influenced by relative fitness, antimicrobial susceptibility, and the underlying mechanism. We have investigated triclosan-induced generation of SCVs in six S. aureus strains, including methicillin-resistant S. aureus (MRSA). Parent strains (P0) were repeatedly passaged on concentration gradients of triclosan using a solid-state exposure system to generate P10. P10 was subsequently passaged without triclosan to generate X10. Susceptibility to triclosan and 7 antibiotics was assessed at all stages. For S. aureus ATCC 6538, SCVs were further characterized by determining microbicide susceptibility and competitive fitness. Cellular morphology was examined using electron microscopy, and protein expression was evaluated through proteomics. Triclosan susceptibility in all SCVs (which could be generated from 4/6 strains) was markedly decreased, while antibiotic susceptibility was significantly increased in the majority of cases. An SCV of S. aureus ATCC 6538 exhibited significantly increased susceptibility to all tested microbicides. Cross-wall formation was impaired in this bacterium, while expression of FabI, a target of triclosan, and IsaA, a lytic transglycosylase involved in cell division, was increased. The P10 SCV was 49% less fit than P0. In summary, triclosan exposure of S. aureus produced SCVs in 4/6 test bacteria, with decreased triclosan susceptibility but with generally increased antibiotic susceptibility. An SCV derived from S. aureus ATCC 6538 showed reduced competitive fitness, potentially due to impaired cell division. In this SCV, increased FabI expression could account for reduced triclosan susceptibility, while IsaA may be upregulated in response to cell division defects.
authors.affiliation: Manchester Pharmacy School, The University of Manchester, Manchester, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Forbes
authors.affiliation: Manchester Pharmacy School, The University of Manchester, Manchester, United Kingdom.
authors.forename: Joe
authors.initials: J
authors.lastname: Latimer
authors.affiliation: Manchester Pharmacy School, The University of Manchester, Manchester, United Kingdom.
authors.forename: Abdulrahman
authors.initials: A
authors.lastname: Bazaid
authors.affiliation: Manchester Pharmacy School, The University of Manchester, Manchester, United Kingdom andrew.mcbain@manchester.ac.uk.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McBain
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests / Q000379:methods; D010641:Phenotype; D040901:Proteomics / Q000379:methods; D013203:Staphylococcal Infections / Q000188:drug therapy; D014260:Triclosan / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D014260:Triclosan