Molecular typing of enterotoxigenic strains of Staphylococcus aureus by pulsed-field gel electrophoresis, ribotyping and random amplified polymorphic DNA anaylsis

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Staphylococcus aureus coagulase type VII strains have been the strains most frequently isolated from staphylococcal food poisoning outbreaks in Japan. We applied pulsed-field gel electrophoresis (PFGE) of chromosomal DNA digested with Smal to characterize 129 coagulase type VII strains. These were isolated from 129 cases occurring in outbreaks in 35 districts of Tokyo during a 16-year period (1980-1995). The 129 outbreak strains were classified into three types, designated A(n=115), B(n=10), and C(n=4). Types A and C were further divided into 33(A1 to A33) and 4(C1 to C4) subtypes, respectively. Strains of the same subtypes were isolated from food poisoning cases in the same districts at time intervals of 1 or 2 to 5 years. PFGE typing appears to be a useful method for subdividing strains of S.aureus coagulase type VII.A combination of coagulase typing and PFGE typing would provide more detailed information than the former method alone in epidemiologic investigations of staphylococcal food poisoning. During the period from January to June in 1998, a total of 180 raw meat samples comprising 100 chicken and 80 pork samples purchased from a supermarket in Hyogo Prefecture were examined for the presence of S.aureus. It was found that 70 (70%) chicken and 29(36%) pork samples were contaminated with S.aureus. PFGE was applied for epidemiological analysis of the isolates. Seventy chicken isolates produced 15 (A-O) different patterns. Various genotypes of S.aureus were found in the chicken. Twenty-nine pork isolates produced 3(A, O, Q) patterns. Interestingly, S.aureus showing the same pattern A was detected most frequently in both the chicken (n=18) and the pork (n=24). In addition, pattern A was isolated repeatedly from the chicken and pork throughout the investigation.