ABSTRACT
Background: staphylococcus enterotoxins [SEs] are super antigenic toxins responsible for food poisoning in human and lead to high incidence of food poisoning outbreaks. The only previously known toxins were the five major classical types SEA to SEE. New types have been identified such as SEG and SEH. Objective: The aim of this work was to evaluate the percentage of S. aureus and enterotoxin productivity in milk and some dairy products, and to characterize the genes encoding some of the classical and the most newly described types of SEs
Materials and methods: 400 samples [200 milk, 100 ice-cream and 100 kariesh cheese samples] in addition to 50 human nasal swabs from handlers of these products were collected from different localities in Assiut Governorate, Egypt and were examined for the presence of S. aureus strains using Baird-Parker agar[BP-A]. Suspected colonies were confirmed as S. aureus by tube coagulase test and detection of clumping factor, protein A and capsular polysaccharides by latex agglutination test. Confirmed S. aureus isolates were examined for the production of SEs by using sodium dodecyl sulphate-polyacrylamide gel electrophoresis [SDS-PAGE]. Enterotoxigenic strains were examined for the presence of SE genes by polymerase chain reaction [PCR] using specific primers for SEA, SEB, SEC, SED, SEG and SHE
Results: confirmed S. aureus isolates were detected in 50% of raw milk, 35% of ice-cream and 65% of kariesh cheese samples and 40% of nasal swabs. Collectively, 50% of S. aureus isolates were enterotoxigenic and the highest percentages were detected in milk taken directly from animals [68. 7%] and kariesh cheese from street distributers [65. 7%]. In milk and dairy products, the major classical enterotoxin genotype was SEA which was detected in 29.3% of toxigenic isolates. SEC was detected in 16.1% and SED in 10.1%. SEB could not be detected. For the newly described genes, SEG was detected in 10.1% and SEH in 7.1%. Mixed forms were found in 2 3.2% of toxigenic isolates and four strains [4. 04%] carried undescribed genes. In nasal swabs, the most common type of SEs was SEA [40%] other types except SEB were detected separately in 10% of toxigenic isolates. The mixed forms were found in 20% of toxigenic isolates
Conclusions: a large proportion of raw milk and some dairy products [especially kariesh cheese] exposed for sale in Assuit City, Egypt are contaminated with enter toxigenic S. aureus. The most common type in both milk and dairy products as well as in nasal swabs was SEA which is known to be less common among strains from animal origin than from human. Nasal carriage in human food handlers is considered a primary source of contamination of milk and dairy products