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Antimicrobial Agents and Chemotherapy, August 2008, p. 2890-2897, Vol. 52, No. 8
0066-4804/08/$08.00+0     doi:10.1128/AAC.00185-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

First Molecular Characterization of Group B Streptococci with Reduced Penicillin Susceptibility {triangledown}

Kouji Kimura,1 Satowa Suzuki,1 Jun-ichi Wachino,1 Hiroshi Kurokawa,1 Kunikazu Yamane,1 Naohiro Shibata,1 Noriyuki Nagano,1,2 Haru Kato,1 Keigo Shibayama,1 and Yoshichika Arakawa1*

Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Disease, Tokyo, Japan,1 Medical Microbiology Laboratory, Funabashi Medical Center, Chiba, Japan2

Received 9 February 2008/ Returned for modification 8 March 2008/ Accepted 5 May 2008

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 µg/ml, 2 to 8 µg/ml, and 4 to 128 µg/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 β-lactam-insusceptible GBS from a phenotypic standpoint.

* Corresponding author. Mailing address: Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan. Phone: 81-42-561-0771, ext. 500. Fax: 81-42-561-7173. E-mail: yarakawa{at}nih.go.jp

{triangledown} Published ahead of print on 19 May 2008.

Antimicrobial Agents and Chemotherapy, August 2008, p. 2890-2897, Vol. 52, No. 8
0066-4804/08/$08.00+0     doi:10.1128/AAC.00185-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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  • Murayama, S. Y., Seki, C., Sakata, H., Sunaoshi, K., Nakayama, E., Iwata, S., Sunakawa, K., Ubukata, K., and the Invasive Streptococcal Disease Working Gro, (2009). Capsular Type and Antibiotic Resistance in Streptococcus agalactiae Isolates from Patients, Ranging from Newborns to the Elderly, with Invasive Infections. Antimicrob. Agents Chemother. 53: 2650-2653 [Abstract] [Full Text]  
  • Nagano, N., Nagano, Y., Kimura, K., Tamai, K., Yanagisawa, H., Arakawa, Y. (2008). Genetic Heterogeneity in pbp Genes among Clinically Isolated Group B Streptococci with Reduced Penicillin Susceptibility. Antimicrob. Agents Chemother. 52: 4258-4267 [Abstract] [Full Text]  
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