The distribution of enterotoxin and enterotoxin-like genes in Staphylococcus aureus strains isolated from nasal carriers and food samples

Staphylococcus aureus strains were examined for the presence of 18 enterotoxin (se) and enterotoxin-like (sel) genes by PCR and four classic enterotoxins SEA to SED by reverse passive latex agglutination. We screened three groups of isolates: 53 recovered from food samples collected in years 2004-2005, 18--from food samples collected in the 1960s and 1970s and 30--from nasal carrier samples collected in the years 2000-2002. Eighty percent of all tested strains were se and sel positive, but the frequency of these genes was higher among nasal carrier strains (93%) than among food samples isolates (circa 76%). The enterotoxin genes cluster (egc) was the most prevalent among carrier strains (18/30-60%) and the least--among food strains isolated in the 1960s and 1970s (6/18 strains--33%). sea coding enterotoxin A, which was recognised as the major cause of staphylococcal food poisoning so far, was more often found among carrier strains than among the years 2004-2005 food strains (27% versus 11%), but it was the most frequent se/sel gene among food strains isolated in the 1960s and 1970s (10/18 strains). Moreover in our results certain se and sel genes coexisted, which was in accordance with current knowledge about movable genetic elements carrying those genes. The exception was for only one strain, which harboured the sole selr gene on a possibly new genetic element not yet described. As we found both types of egc, as well as seh (especially food samples strains) occurred alone in a majority of positive strains for each of those genes. The analysis of the results obtained by SET-RPLA method for the productivities of classical enterotoxins A-D and the results obtained by PCR for the presence of sea-sed genes revealed the correlation between each other. Only three of all sea-sed positive strains had silent genes--sed.