title: Mutations are involved in emergence of aminoglycoside-induced small colony variants of Staphylococcus aureus.
abstract: Staphylococcus aureus small colony variants (SCVs) occur frequently after local treatment with aminoglycosides and cause persistent as well as recurrent infections. So far, the molecular mechanism of the emergence of SCVs is not understood and regulatory as well as genetic mechanisms seem conceivable. To screen for possible mutations, the hemin biosynthetic gene cluster of a gentamicin-induced SCV was sequenced and was found to contain a deletion in the gene hemH. To further assess the influence of a high mutation rate on the development of SCVs, we tested the emergence of SCVs in a strain that had been inactivated in the DNA proofreading enzyme MutS. In the mutant, spontaneous SCVs emerged 556-fold more frequently than in the parent strain. By incubation in the presence of subinhibitory concentrations of gentamicin, the SCV frequency in the parent strain could be increased to 9.7 x 10(-6), whereas it remained rather stable in the mutant (1.8 x 10(-5)). Eighty percent of the gentamicin-induced SCVs were hemin auxotrophic in contrast to only 20% of the spontaneous SCVs which may explain the large proportion of hemin auxotrophs among clinical SCVs from patients previously treated with aminoglycosides. Additionally, a clinical S. aureus SCV isolate with a mutator phenotype, indicated by the generation of rifampicin-resistant mutants at a 16-fold higher frequency than in the reference strain S. aureus NCTC 8325, was characterized. The results demonstrate that a high mutation rate favours the emergence of SCVs, and suggest that mutations in general play an important role in the development of SCVs.
authors.affiliation: Institute of Medical Microbiology and Immunology, University of Bonn, Bonn, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Schaaff
authors.forename: Gabriele
authors.initials: G
authors.lastname: Bierbaum
authors.forename: Nicole
authors.initials: N
authors.lastname: Baumert
authors.forename: Peter
authors.initials: P
authors.lastname: Bartmann
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Sahl
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D015169:Colony Count, Microbial; D003470:Culture Media; D005839:Gentamicins / Q000494:pharmacology*; D006427:Hemin / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003470:Culture Media; D005839:Gentamicins; D006427:Hemin