Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a Tokyo hospital in 2000.

*Corresponding author: Mailing address: International Medical Center of Japan, Toyama 1-21-1, Shinjuku-ku, Tokyo 162-8655, Japan. Fax: +81-3-3202-7181, E-mail: [email protected] Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important nosocomial pathogens in healthcare facilities. Epidemiological analysis is therefore indispensable for assessing infection control measures (1-3). In October 2003, 241 MRSA isolates were obtained from 72 inpatients in a hospital with 24 wards and 925 beds in Tokyo. Among the samples, 65 were derived from a single patient and were analyzed in terms of the following: chromosomal DNA typing with a contour-clamped homogeneous electric field system (CHEF Mapper: Bio-Rad Laboratories, Hercules, Calif., USA), antibiotic resistance (WalkAway: Dade Behring, Greefield, Ill., USA), enterotoxin serotyping (SET-RPLA: Denka Seiken Co., Tokyo), toxic shock syndrome toxin-1 (TSST-1) production (TST-RPLA: Denka Seiken), and coagulase serotyping (Denka Seiken). Isolates showing the same pulsed-field gel electrophoresis (PFGE) patterns were probably of the same origin. Thirty-eight different PFGE patterns of SmaI DNA digests were detected (Fig. 1). A band-based cluster analysis (Molecular Analyst: Bio-Rad), in which PFGE-band similarity exceeding 70% was used as the criterion for cluster formation, revealed the following 15 clusters: A, AT, Y, AU, AV, AB, AW, AE, AX, J, AY, AZ, BA, BB, and BC (Fig. 2A). The frequency distribution of these different PFGE-pattern isolates of MRSA is shown in Fig. 2B. Cluster A was the cluster type of 50% of the total isolates, and the most frequent pattern was A1, which represented 17% of the isolates. The distribution of MRSA isolates in this study is shown in Table 1. Isolates belonging to cluster A were found in 14 of 24 wards; more specifically, PFGE pattern A1 was identified in 10 wards, pattern A3 in four wards, and patterns A4 and A29 in two wards, respectively. Pattern Y4 was found in two wards. The sensitivity to antibiotics is shown in Table 2. Fifteen different patterns were identified. The isolates were found to be resistant to 8 -13 of 18 tested drugs. None of the isolates were resistant to vancomycin, teicoplanin, nor sulfamethoxazole/trimethoprim. All of the 11 isolates with pattern A1 had an antibiotic pattern of j, k, or ab. No correlation was found between the antibiotic patterns and PFGE patterns. Among 65 isolates, 61 produced coagulase type II, three isolates produced coagulase type IV, and one produced coagulase type III. Forty-four isolates produced enterotoxin type C, nine isolates enterotoxin type B, four isolates enterotoxin types B and C, and one isolate enterotoxin type A, while the remaining seven isolates produced no enterotoxins. Fifty isolates produced TSST-1, but 15 did not. Collectively, among 65 MRSA isolates, 44 produced coagulase type II, enterotoxin type C, and TSST-1.