title: First molecular characterization of group B streptococci with reduced penicillin susceptibility.
abstract: Group B streptococci (GBS; Streptococcus agalactiae) are the leading cause of neonatal invasive diseases and are also important pathogens for adults. Penicillins are the drugs of first choice for the treatment of GBS infections, since GBS have been regarded to be uniformly susceptible to penicillins so far. Here we characterize the first strains of GBS with reduced penicillin susceptibility (PRGBS) identified in Japan. Fourteen PRGBS strains were clinically isolated from the sputa of elderly patients from 1995 to 2005; and the MICs of penicillin, oxacillin, and ceftizoxime ranged from 0.25 to 1 microg/ml, 2 to 8 microg/ml, and 4 to 128 microg/ml, respectively. Moreover, some strains were also insusceptible to ampicillin, cefazolin, cefepime, and cefotaxime. All the PRGBS isolates tested possessed a few amino acid substitutions adjacent to the conserved SSN and KSG motifs (amino acids 402 to 404 and 552 to 554, respectively) of PBP 2X, and the amino acid substitutions could be classified into two types, Q557E and V405A. Western blotting analysis of the 14 clinical isolates with anti-PBP 2X-specific serum suggested that the amount of PBP 2X among the 14 PRGBS isolates was reduced, although the 2 ATCC strains produced a significant amount of PBP 2X. The introduction of PRGBS-derived PBP 2X genes into penicillin-susceptible strains through allelic exchange elevated their penicillin insusceptibility, suggesting that these altered PBP 2X genes are responsible for the penicillin insusceptibility in PRGBS strains. In this study, we characterized for the first time PRGBS strains on a molecular basis, although several reports have so far mentioned the existence of beta-lactam-insusceptible GBS from a phenotypic standpoint.
authors.affiliation: Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan.
authors.forename: Kouji
authors.initials: K
authors.lastname: Kimura
authors.forename: Satowa
authors.initials: S
authors.lastname: Suzuki
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Wachino
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kurokawa
authors.forename: Kunikazu
authors.initials: K
authors.lastname: Yamane
authors.forename: Naohiro
authors.initials: N
authors.lastname: Shibata
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nagano
authors.forename: Haru
authors.initials: H
authors.lastname: Kato
authors.forename: Keigo
authors.initials: K
authors.lastname: Shibayama
authors.forename: Yoshichika
authors.initials: Y
authors.lastname: Arakawa
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D000077723:Cefepime; D002439:Cefotaxime / Q000494:pharmacology; D015296:Ceftizoxime / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007564:Japan; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010068:Oxacillin / Q000494:pharmacology; D010403:Penicillin Resistance / Q000235:genetics; D046915:Penicillin-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D010406:Penicillins / Q000494:pharmacology*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013290:Streptococcal Infections / Q000382:microbiology; D013292:Streptococcus agalactiae / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D000667:Ampicillin; D000077723:Cefepime; D015296:Ceftizoxime; D002439:Cefotaxime; D010068:Oxacillin