title: Clonal relatedness is a predictor of spontaneous multidrug efflux pump gene overexpression in Staphylococcus aureus.
abstract: Increased expression of genes encoding multidrug resistance efflux pumps (MDR-EPs) contributes to antimicrobial agent and biocide resistance in Staphylococcus aureus. Previously identified associations between norA overexpression and spa type t002 meticillin-resistant S. aureus (MRSA), and a similar yet weaker association between mepA overexpression and type t008 meticillin-susceptible S. aureus (MSSA), in clinical isolates are suggestive of clonal dissemination. It is also possible that related strains are prone to mutations resulting in overexpression of specific MDR-EP genes. Exposure of non-MDR-EP-overexpressing clinical isolates to biocides and dyes can select for MDR-EP-overexpressing mutants. spa types t002 and t008 isolates are predominated by multilocus sequencing typing sequence types (STs) 5 and 8, respectively. In this study, non-MDR-EP gene-overexpressing clinical isolates (MRSA and MSSA) representing ST5 and ST8 were subjected to single exposures of ethidium bromide (EtBr) to select for EtBr-resistant mutants. Measurements of active EtBr transport among mutants were used to demonstrate an efflux-proficient phenotype. Using quantitative reverse-transcription PCR, it was found that EtBr-resistant mutants of ST5 and ST8 parental strains predominantly overexpressed mepA (100%) and mdeA (83%), respectively, regardless of meticillin sensitivity. Associations between clonal lineage and MDR-EP gene overexpression differed from those previously observed and suggest the latter is due to clonal spread of efflux-proficient strains. The predilection of in vitro-selected mutants of related strains to overexpress the same MDR-EP gene indicates the presence of a consistent mutational process.
authors.affiliation: The John D. Dingell Department of Veterans Affairs Medical Center, Detroit, MI 48201, USA.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Schindler
authors.affiliation: Department of Internal Medicine, Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, MI 48201, USA.
authors.forename: Pauline L
authors.initials: PL
authors.lastname: Jacinto
authors.affiliation: Department of Internal Medicine, Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, MI 48201, USA.
authors.forename: Joseph Adrian L
authors.initials: JA
authors.lastname: Buensalido
authors.affiliation: The John D. Dingell Department of Veterans Affairs Medical Center, Detroit, MI 48201, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Seo
authors.affiliation: The John D. Dingell Department of Veterans Affairs Medical Center, Detroit, MI 48201, USA; Department of Internal Medicine, Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, MI 48201, USA. Electronic address: gkaatz@juno.com.
authors.forename: Glenn W
authors.initials: GW
authors.lastname: Kaatz
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D001693:Biological Transport, Active; D024901:Drug Resistance, Multiple, Bacterial; D004996:Ethidium / Q000378:metabolism; D015870:Gene Expression; D020869:Gene Expression Profiling; D019450:Genes, MDR; D005838:Genotype; D006801:Humans; D012641:Selection, Genetic; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000635:transmission*; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D004996:Ethidium
keywords: Antibiotic resistance; Efflux; Ethidium bromide; Gene overexpression; Staphylococcus aureus; spa Type