APPLICATION OF PULSED-FIELD GEL-ELECTROPHORESIS TO THE EPIDEMIOLOGIC CHARACTERIZATION OF STAPHYLOCOCCUS-INTERMEDIUS IMPLICATED IN A FOOD-RELATED OUTBREAK

Bn outbreak of food intoxication involving over 265 cases in western U nited States occurred in October 1991. Staphylococcus intermedius was implicated as the aetiologic agent. Representative outbreak isolates ( five clinical and ten from foods) produced type A enterotoxin. DNA fra gments generated by four restriction endonucleases and analysed by pul sed-field gel electrophoresis (PFGE) provided definitive evidence that all isolates from nine different counties in California and Nevada we re derived from a single strain. The PFGE pattern of these outbreak is olates was distinct from those of a heterogeneous collection of seven S. intermedius strains of veterinary origin and five unrelated S. aure us laboratory strains. The data show a significant PFGE pattern hetero geneity not only among members of different Staphylococcus species but also within members of the same species and even the same enterotoxin type. The results indicate that PFGE is a valuable strain-specific di scriminator for the epidemiological characterization of S. intermedius . To our knowledge, this represents the first documented foodborne out break caused by S. intermedius. These findings suggest that the presen ce of S. intermedius and other species such as S. hyicus in food shoul d be reason for concern.