Phenotypic and genotypic characterization of Staphylococcus aureus strains isolated from a familial foodborne outbreak

Abstract

Although Staphylococcus aureus is frequently reported among the common causative agents of foodborne diseases in Europe, very little is known about the strains involved in staphylococcal food-poisoning outbreaks in our region. Therefore, the aim of this study was to characterize the staphylococcal strains recovered from an autochthonous food-poisoning familial outbreak through phenotypic and genotypic methods. Ten S. aureus strains from food and human sources, submitted to the reference laboratory, were tested for susceptibility to 18 antibiotics by disk diffusion and production of enterotoxins A, B, C, D using a reversed passive latex-agglutination assay, and further analyzed by multiplex PCR-based assays for the detection of sea, seb, sec, sed, see, seh, sei, sej, sem, and sen genes. Phage typing, pulsed-field gel electrophoresis (PFGE) and spa typing were performed for evaluating the clonal relatedness of the isolates. Isolates from stool samples and food displayed a similar antibiotic resistance profile, produced enterotoxin B, were PCR-positive for seb, sei and sem genes, and revealed an indistinguishable SmaI macrorestriction pattern at PFGE analysis, suggesting that incriminated food was most likely the source of this food poisoning outbreak. The isolate which expressed a different antibiotic susceptibility profile and tested negative at the screening for enterotoxin production carried seh gene and was discriminated by a nine-band different PFGE profile from the rest. Combined phenotypic and genotypic profiles by multiple typing are necessary to explore key features of epidemic strains and start to lead to a better understanding of the local epidemiology of infections due to toxigenic S. aureus strains.