title: Dissemination of Novel Antimicrobial Resistance Mechanisms through the Insertion Sequence Mediated Spread of Metabolic Genes.
abstract: The widely used biocide triclosan selectively targets FabI, the NADH-dependent trans-2-enoyl-acyl carrier protein (ACP) reductase, which is also an important target for the development of narrow spectrum antibiotics. The analysis of triclosan resistant Staphylococcus aureus isolates had previously shown that in about half of the strains, the mechanism of triclosan resistance consists on the heterologous duplication of the triclosan target gene due to the acquisition of an additional fabI allele derived from Staphylococcus haemolyticus (sh-fabI). In the current work, the genomic sequencing of 10 of these strains allowed the characterization of two novel composite transposons TnSha1 and TnSha2 involved in the spread of sh-fabI. TnSha1 harbors one copy of IS1272, whereas TnSha2 is a 11.7 kb plasmid carrying TnSha1 present either as plasmid or in an integrated form generally flanked by two IS1272 elements. The target and mechanism of integration for IS1272 and TnSha1 are novel and include targeting of DNA secondary structures, generation of blunt-end deletions of the stem-loop and absence of target duplication. Database analyses showed widespread occurrence of these two elements in chromosomes and plasmids, with TnSha1 mainly in S. aureus and with TnSha2 mainly in S. haemolyticus and S. epidermidis. The acquisition of resistance by means of an insertion sequence-based mobilization and consequent duplication of drug-target metabolic genes, as observed here for sh-fabI, is highly reminiscent of the situation with the ileS2 gene conferring mupirocin resistance, and the dfrA and dfrG genes conferring trimethoprim resistance both of which are mobilized by IS257. These three examples, which show similar mechanisms and levels of spread of metabolic genes linked to IS elements, highlight the importance of this genetic strategy for recruitment and rapid distribution of novel resistance mechanisms in staphylococci.
authors.affiliation: Department of Genetics, University of LeicesterLeicester, UK; Dipartimento di Biotecnologie Mediche, Universita di SienaSiena, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Furi
authors.affiliation: Department of Genetics, University of Leicester Leicester, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Haigh
authors.affiliation: Department of Genetics, University of Leicester Leicester, UK.
authors.forename: Zaaima J H
authors.initials: ZJ
authors.lastname: Al Jabri
authors.affiliation: IHMA Europe Sàrl Epalinges, Switzerland.
authors.forename: Ian
authors.initials: I
authors.lastname: Morrissey
authors.affiliation: State Key Laboratory for Microbial Metabolism and School of Life Sciences and Biotechnology, Shanghai Jiaotong University Shanghai, China.
authors.forename: Hong-Yu
authors.initials: HY
authors.lastname: Ou
authors.affiliation: Departamento de Microbiología, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y CajalMadrid, Spain; Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública (CIBERESP)Spain.
authors.forename: Ricardo
authors.initials: R
authors.lastname: León-Sampedro
authors.affiliation: Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones CientíficasMadrid, Spain; Unidad de Resistencia a Antibióticos y Virulencia Bacteriana (RYC-Consejo Superior de Investigaciones Científicas)Madrid, Spain.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Martinez
authors.affiliation: Departamento de Microbiología, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y CajalMadrid, Spain; Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública (CIBERESP)Spain; Unidad de Resistencia a Antibióticos y Virulencia Bacteriana (RYC-Consejo Superior de Investigaciones Científicas)Madrid, Spain.
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Coque
authors.affiliation: Department of Genetics, University of LeicesterLeicester, UK; Dipartimento di Biotecnologie Mediche, Universita di SienaSiena, Italy.
authors.forename: Marco R
authors.initials: MR
authors.lastname: Oggioni
keywords: IS1182 family; IS5 family; antimicrobial drug resistance; fabI; insertion sequence; metabolism; resistance risk; transposon