Institute of Anaerobic Bacteriology, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8705, Japan
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Abstract |
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Introduction |
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CS-834 is an oral carbapenem newly synthesized by Sankyo Co., Ltd (Tokyo, Japan). R-95867 is the active metabolite of this compound. Here we compared the in vitro activity of R-95867 with other oral agents against a variety of anaerobic bacteria. The stability of R-95867 to hydrolysis by ß-lactamases produced by anaerobic strains was also examined.
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Materials and methods |
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A total of 513 clinical isolates of strictly anaerobic bacteria were tested for antimicrobial susceptibility. The clinical isolates were randomly collected from numerous clinical laboratories in Japan between 1992 and 1996. All strains were identified by a combination of standard methods and the RapID ANA II (Innovative Diagnostic Systems, Atlanta, GA, USA) or Rapid ID 32A (bioMérieux, Marcy-l'Etoile, France).
NCCLS guidelines for agar dilution susceptibility testing of anaerobes3 were used throughout the studies, with a few exceptions. Brucella HK agar (Kyokuto Pharmaceutical Co., Tokyo, Japan) supplemented with 5% laked sheep blood was used as test medium. B. fragilis ATCC 25285 and GAI 5562 were used as quality control strains. Plates were incubated for 2 days at 37°C in an anaerobic chamber (Hirasawa, Tokyo, Japan) with an atmosphere consisting of 82% N2, 10% CO2 and 8% H2.
Effect of medium pH on in vitro activity
A broth microdilution method recommended by NCCLS3 was used to study the effect of medium pH on in vitro activity. Anaerobe broth MIC medium (Difco Laboratories, Detroit, MI, USA) was adjusted with 0.2 M 3-[morpholino]-propanesulphonic acid to pH 7.5, 7.0, 6.5, 6.0 or 5.5. Strains used were ATCC 25285 and seven clinical isolates of B. fragilis. Inoculated microtitre plates were incubated for 2 days at 37°C in the anaerobic conditions described above. The concentration where the most significant reduction of growth was observed was read as the end point.
Crude ß-lactamases were prepared from four strains of B. fragilis, two strains of Prevotella bivia and one strain of Prevotella intermedia. These strains produce ß-lactamase group 2e, except for a single B. fragilis strain that produces ß-lactamase group 3 (carbapenemase); ß-lactamases were categorized using the scheme of Bush.4 The antimicrobial agents used were cephaloridine (Shionogi & Co., Osaka, Japan), R-95867 (Sankyo), imipenem (Banyu Pharmaceutical Co., Tokyo, Japan), cefditoren (Meiji Seika Kaisha) and cefdinir (Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan). ß-Lactamase hydrolysis assay was performed by a spectrophotometric technique as described previously.5 The relative hydrolysis rate of each compound was expressed as a percentage of the hydrolysis rate of cephaloridine.
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Results and discussion |
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The decrease in the pH of the medium was accompanied by an increase in the activity of R-95867 (2- to 8-fold decrease in MICs) but also a gradual decrease in the activity of clindamycin (4- to 8-fold increase in MICs) against B. fragilis strains. R-95867 was 2- to 4-fold more active than clindamycin against seven of the eight strains of B. fragilis tested at pH 6.5. Intra-abdominal abscesses were found to have a wide pH range of 5.56.8.7 This may be an advantage for the in vivo activity of R-95867.
R-95867 and imipenem were stable to hydrolysis by ß-lactamase type 2e but not carbapenemase (Table II). ß-Lactamase-producing Prevotella and Porphyromonas strains showed poor susceptibility to many ß-lactam antibiotics. Our results demonstrated that R-95867 was not hydrolysed at all by ß-lactamases produced by P. bivia and P. intermedia strains.
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CS-834 warrants clinical trials to evaluate its efficacy against infections with which anaerobic and aerobic bacteria are associated.
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Notes |
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Present address. Department of Bacteriology, School of Medicine, Kanazawa University, 13 Takara-machi, Kanazawa 920-8640, Japan.
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References |
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2 . Appelbaum, P. C., Spangler, S. K. & Jacobs, M. R. (1993). Susceptibility of 539 Gram-positive and Gram-negative anaerobes to new agents, including RP59500, biapenem, trospectomycin and piperacillin/tazobactam. Journal of Antimicrobial Chemotherapy 32, 22331.[Abstract]
3 . National Committee for Clinical Laboratory Standards. (1993). Methods for Antimicrobial Susceptibility Testing of Anaerobic BacteriaThird Edition: Approved Standard M11-A3. NCCLS, Villanova, PA.
4 . Bush, K. (1989). Classification of ß-lactamases: groups 2c, 2d, 2e, 3, and 4. Antimicrobial Agents and Chemotherapy 33, 2716.[ISI][Medline]
5 . Bandoh, K., Muto, Y., Watanabe, K., Katoh, N. & Ueno, K. (1991). Biochemical properties and purification of metallo-ß-lactamase from Bacteroides fragilis. Antimicrobial Agents and Chemotherapy 35, 3712.[ISI][Medline]
6 . Fukuoka, T., Ohya, S., Utsui, Y., Domon, H., Takenouchi, T. & Koga, T. (1997). In vitro and in vivo antibacterial activities of CS-834, a novel oral carbapenem. Antimicrobial Agents and Chemotherapy 41, 265263.[Abstract]
7 . Bryant, R. E. (1984). Effect of the suppurative environment on antibiotic activity. In New Dimensions of Antimicrobial Therapy (Root, R. K. & Sande, M. A., Eds), pp. 31357. Churchill Livingstone, New York.
8 . Umemura, K., Ikeda, Y., Kondo, K., Nakashima, M., Naganuma, H. & Hisaoka, M. (1997). Safety and pharmacokinetics of CS-834, a new oral carbapenem antibiotic, in healthy volunteers. Antimicrobial Agents and Chemotherapy 41, 26649.[Abstract]
Received 28 June 1999; returned 23 September 1999; revised 20 October 1999; accepted 16 November 1999