title: Amino acid substitutions in mosaic penicillin-binding protein 2 associated with reduced susceptibility to cefixime in clinical isolates of Neisseria gonorrhoeae.
abstract: The molecular mechanisms of reduced susceptibility to cefixime in clinical isolates of Neisseria gonorrhoeae, particularly amino acid substitutions in mosaic penicillin-binding protein 2 (PBP2), were examined. The complete sequence of ponA, penA, and por genes, encoding, respectively, PBP1, PBP2, and porin, were determined for 58 strains isolated in 2002 from Japan. Replacement of leucine 421 by proline in PBP1 and the mosaic-like structure of PBP2 were detected in 48 strains (82.8%) and 28 strains (48.3%), respectively. The presence of mosaic PBP2 was the main cause of the elevated cefixime MIC (4- to 64-fold). In order to identify the mutations responsible for the reduced susceptibility to cefixime in isolates with mosaic PBP2, penA genes with various mutations were transferred to a susceptible strain by genetic transformation. The susceptibility of partial recombinants and site-directed mutants revealed that the replacement of glycine 545 by serine (G545S) was the primary mutation, which led to a two- to fourfold increase in resistance to cephems. Replacement of isoleucine 312 by methionine (I312M) and valine 316 by threonine (V316T), in the presence of the G545S mutation, reduced susceptibility to cefixime, ceftibuten, and cefpodoxime by an additional fourfold. Therefore, three mutations (G545S, I312M, and V316T) in mosaic PBP2 were identified as the amino acid substitutions responsible for reduced susceptibility to cefixime in N. gonorrhoeae.
authors.affiliation: Pharmaceutical Research Center, Meiji Seika Kaisha, Ltd., 760 Morooka-cho, Kohoku-ku, Yokohama 222-8567, Japan. sho_takahata@meiji.co.jp
authors.forename: Sho
authors.initials: S
authors.lastname: Takahata
authors.forename: Nami
authors.initials: N
authors.lastname: Senju
authors.forename: Yumi
authors.initials: Y
authors.lastname: Osaki
authors.forename: Takuji
authors.initials: T
authors.lastname: Yoshida
authors.forename: Takashi
authors.initials: T
authors.lastname: Ida
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics; D020682:Cefixime / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D003001:Cloning, Molecular; D024881:Drug Resistance, Bacterial / Q000235:genetics; D006069:Gonorrhea / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009344:Neisseria gonorrhoeae / Q000187:drug effects* / Q000235:genetics*; D046915:Penicillin-Binding Proteins / Q000235:genetics; D018272:Porins / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014170:Transformation, Genetic
chemical_list: D001426:Bacterial Proteins; D002511:Cephalosporins; D046915:Penicillin-Binding Proteins; D018272:Porins; C057699:porin protein, Neisseria; D020682:Cefixime