Application of pulsed-field gel electrophoresis to the epidemiological characterization ofStaphylococcus intermediusimplicated in a food-related outbreak

Abstract

SUMMARYAn outbreak of food intoxication involving over 265 cases in western United States occurred in October 1991.Staphylococcus intermediuswas implicated as the aetiologic agent. Representative outbreak isolates (five clinical and ten from foods) produced type A enterotoxin. DNA fragments generated by four restriction endonucleases and analysed by pulsed-field gel electrophoresis (PFGE) provided definitive evidence that all isolates from nine different counties in California and Nevada were derived from a single strain. The PFGE pattern of these outbreak isolates was distinct from those of a heterogeneous collection of sevenS. intermediusstrains of veterinary origin and five unrelatedS. aureuslaboratory strains. The data show a significant PFGE pattern heterogeneity not only among members of differentStaphylococcusspecies but also within members of the same species and even the same enterotoxin type. The results indicate that PFGE is a valuable strain-specific discriminator for the epidemiological characterization ofS. intermedius. To our knowledge, this represents the first documented foodborne outbreak caused byS. intermedius. These findings suggest that the presence ofS. intermediusand other species such asS. hyicusin food should be reason for concern.