title: Antimicrobial susceptibility and mechanisms of high-level macrolide resistance in clinical isolates of Moraxella nonliquefaciens.
abstract: We investigated antimicrobial susceptibility and the molecular mechanism involved in conferring high-level macrolide resistance in 47 clinical isolates of Moraxella nonliquefaciens from Japan. Antimicrobial susceptibility was determined using Etest and agar dilution methods. Thirty-two erythromycin-non-susceptible strains were evaluated for the possibility of clonal spreading, using PFGE. To analyse the mechanism related to macrolide resistance, mutations in the 23S rRNA gene and the ribosomal proteins, and the presence of methylase genes were investigated by PCR and sequencing. The efflux system was examined using appropriate inhibitors. Penicillin, ampicillin, amoxicillin, cefixime, levofloxacin and antimicrobials containing β-lactamase inhibitors showed strong activity against 47 M. nonliquefaciens isolates. Thirty-two (68.1 %) of the 47 isolates showed high-level MICs to macrolides (MIC ≥128 mg l(-1)) and shared the A2058T mutation in the 23S rRNA gene. The geometric mean MIC to macrolides of A2058T-mutated strains was significantly higher than that of WT strains (P<0.0001). Thirty-two isolates with high-level macrolide MICs clustered into 30 patterns on the basis of the PFGE dendrogram, indicating that the macrolide-resistant strains were not clonal. In contrast, no common mutations of the ribosomal proteins or methylase genes, or overproduction of the efflux system were observed in A2058T-mutated strains. Moreover, of the 47 M. nonliquefaciens strains, 43 (91.5 %) were bro-1 and 4 (8.5 %) were bro-2 positive. Our results suggest that most M. nonliquefaciens clinical isolates show high-level macrolide resistance conferred by the A2058T mutation in the 23S rRNA gene. This study represents the first characterization of M. nonliquefaciens.
authors.affiliation: Department of Microbiology and Immunology, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Shotaro
authors.initials: S
authors.lastname: Nonaka
authors.affiliation: Department of Microbiology and Immunology, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Matsuzaki
authors.affiliation: Department of Microbiology and Immunology, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Kazama
authors.affiliation: Clinical Laboratory Department, Surugadai Nihon University Hospital, Tokyo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nishiyama
authors.affiliation: Department of Clinical Laboratory, Kyorin University Hospital, Tokyo, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Ida
authors.affiliation: Department of Infection Control and Prevention, The University of Tokyo Hospital, Tokyo, Japan.
authors.forename: Saho
authors.initials: S
authors.lastname: Koyano
authors.affiliation: Department of Clinical Laboratory, Nippon Medical School, Tokyo, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Sonobe
authors.affiliation: Department of Microbiology and Immunology, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Noboru
authors.initials: N
authors.lastname: Okamura
authors.affiliation: Department of Microbiology and Immunology, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Saito
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007564:Japan; D018942:Macrolides / Q000494:pharmacology*; D008780:Methyltransferases / Q000235:genetics; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D009016:Moraxella / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D045828:Moraxellaceae Infections / Q000382:microbiology*; D009154:Mutation; D016133:Polymerase Chain Reaction; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D012338:RNA, Ribosomal, 23S; D012269:Ribosomal Proteins; D008780:Methyltransferases; C035181:rRNA (adenosine-O-2'-)methyltransferase