title: Genomic analysis of reduced susceptibility to tigecycline in Enterococcus faecium.
abstract: Tigecycline (TIG) is approved for use for the treatment of complicated intra-abdominal infections, skin and skin structure infections, as well as pneumonia. Acquired resistance or reduced susceptibility to TIG has been observed in Gram-negative rods, has seldom been reported in Gram-positive organisms, and has not yet been reported in Enterococcus faecium. Using the serial passage method, in vitro mutant AusTig and in vitro mutants HMtig1 and HMtig2 with decreased TIG susceptibility (MICs, 0.25 μg/ml) were obtained from strains E. faecium Aus0004 and HM1070 (MICs, 0.03 μg/ml), respectively. In addition, two vancomycin-resistant E. faecium clinical isolates (EF16 and EF22) with reduced susceptibility to TIG (MICs, 0.5 and 0.25 μg/ml, respectively) were studied. Compared to the wild-type strains, the in vitro mutants also showed an increase in the MICs of other tetracyclines. An efflux mechanism did not seem to be involved in the reduced TIG susceptibility, since the presence of efflux pump inhibitors (reserpine or pantoprazole) did not affect the MICs of TIG. Whole-genome sequencing of AusTig was carried out, and genomic comparison with the Aus0004 genome was performed. Four modifications leading to an amino acid substitution were found. These mutations affected the rpsJ gene (efau004_00094, coding for the S10 protein of the 30S ribosomal subunit), efau004_01228 (encoding a cation transporter), efau004_01636 (coding for a hypothetical protein), and efau004_02455 (encoding the l-lactate oxidase). The four other strains exhibiting reduced TIG susceptibility were screened for the candidate mutations. This analysis revealed that three of them showed an amino acid substitution in the same region of the RpsJ protein. In this study, we characterized for the first time genetic determinants linked to reduced TIG susceptibility in enterococci.
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France CHU de Caen, Service de Microbiologie, Caen, France CNR de la Résistance aux Antibiotiques, Laboratoire Associé Entérocoques, Caen, France cattoir-v@chu-caen.fr.
authors.forename: Vincent
authors.initials: V
authors.lastname: Cattoir
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France CHU de Caen, Service de Microbiologie, Caen, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Isnard
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France.
authors.forename: Thibaud
authors.initials: T
authors.lastname: Cosquer
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France.
authors.forename: Arlène
authors.initials: A
authors.lastname: Odhiambo
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France.
authors.forename: Fiona
authors.initials: F
authors.lastname: Bucquet
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France CHU de Caen, Service de Microbiologie, Caen, France CNR de la Résistance aux Antibiotiques, Laboratoire Associé Entérocoques, Caen, France.
authors.forename: François
authors.initials: F
authors.lastname: Guérin
authors.affiliation: Université de Caen Basse-Normandie, EA4655 U2RM (Équipe Antibio-Résistance), Caen, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Giard
mesh_terms: D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D016680:Genome, Bacterial; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D009154:Mutation; D012269:Ribosomal Proteins / Q000235:genetics; D013753:Tetracycline Resistance / Q000235:genetics; D000078304:Tigecycline
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D012269:Ribosomal Proteins; D000078304:Tigecycline; D008911:Minocycline