Comparison of genomic DNA fingerprinting using pulsed-field gel electrophoresis and antibiotic susceptibility of clinical isolates of methicillin-resistant Staphylococcus aureus between Chiang Mai and Tokyo.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen in both Thailand and Japan ( 1 -3)・ Genomic DNA fingerpnntlng uSlng Pulsed-field gel electrophoresis (PFGE) is a powerful tool to investigate the source, transmission, and spread of MRSA infection (4). Nine and sixteen MRSA isolates obtained respectively from patients in a universlty hospital in Chiang Mai, Thailand (January to February 2000) and from patients in a hospital (with about 900 beds) in Tokyo (February 1999 to February 2000) were analyzed for chromosomal DNAtype (Contourclamped homogeneous electriCfield system; CHEF MapperTM: Bio-Rad Laboratories, Hercules, Calif., USA), antibiotic resistance (WalkAwayTM, Dade Behring, Deerfield, Ill., USA), enterotoxin serotype (SET-RPLA: Denka Seiken Cot, Tokyo), toxic shock syndrome toxin-I (TSST-1) production (TSTRPLA: Denka Seiken), and coagulase serotype (Denka Seiken). Isolates &om Chiang Maishowed 5 different PFGE patterns and 7 different antibiotic pattems (Fig. 1 and Table 1). Bandbased clusteranalysis of PFGE pattems (MolecularAnalystTM : BioIRad) revealed a more than 94% simiIarityamongthe five isolates (Fig. 2). Chiang Mai isolates with PFGE pattem A,