Occurrence and characterization of enterotoxigenic staphylococci isolated from soft cheeses in Serbia

Abstract

A total of 415 cheese samples produced with raw or cooked milk collected from local markets were analysed for the presence of coagulase-positive staphylococci. In 85 (20.48%) samples the presence of coagulase positive staphylococci was detected. The ELFA technique VIDAS SET2 (BioMerieux, France) was used for testing coagulasepositive staphylococci strains to produce classical enterotoxins (SEA, SEB, SEC, SED, SEE), and to determine the enterotoxins in cheese samples. The number of coagulasepositive staphylococci in cheese samples ranged from 1-5.79 log CFU g-1. Out of 85 coagulase-positive strains 26 (30.59%) produced enterotoxins. The presence of genes for the synthesis of staphylococcal enterotoxins (SE) in the obtained extracts of DNA from 26 enterotoxigenic strains was detected by conventional multiplex PCR technique (for genes sea and seb) i.e. the Real-Time PCR technique for genes sec, sed and see. In all 26 strains of coagulase-positive staphylococci (originating from cheeses produced from raw or cooked milk, which were enterotoxin producers) sea was present, and in 24 strains in addition to sea gene, seb was detected. None of the isolates possessed genes for the synthesis of enterotoxin C (SEC), D (SED) and E (SEE). Out of 26 tested cheese samples positive for enterotoxigenic coagulase-positive staphylococci, enterotoxin was detected in 2 (7.69%) samples of sweet-coagulating cheese, in which the number of enterotoxigenic coagulase-positive staphylococci exceeded 5 log CFU g-1. In sweetcoagulating cheeses in which the number of coagulase-positive staphylococci exceeds 5 log CFU g-1 and the pH value was higher than 5.0, enterotoxins may be present in amounts sufficient to cause intoxication.

Ukupno 415 uzoraka sireva proizvedenih od sirovog ili kuvanog mleka, prikupljenih sa pijaca ispitano je na prisustvo koagulaza pozitivnih stafilokoka. U 80 (20,48%) uzoraka je dokazano prisustvo koagulaza pozitivnih stafilokoka. Za ispitivanje sposobnosti koagulaza pozitivnih stafilokoka da stvaraju enterotoksine (SEA, SEB, SEC, SED, SEE) i dokazivanje enterotoksina u uzorcima sireva korišćena je ELFA tehnika VIDAS SET 2 (BioMerieux, Francuska). Broj koagulaza pozitivnih stafilokoka u zorcima sireva se kretao od 1-5,79 log CFU g-1. Od 85 izolata koagulaza pozitivnih stafilokoka 26 (30,59) je stvaralo enterotoksine. Prisustvo gena za sintezu enterotoksina (SE) u dobijenim ekstraktima DNK iz 26 enterotosogenih izolata je dokazano konvencionalnom multipleks PCR tehnikaom (za gene sea i seb), dok je za genes sec, sed i see korišćena Real-Time PCR tehnika. Kod svih 26 izolata koagulaza pozitivnih stafilokoka (poreklom iz sireva proizvedenih od sirovog ili kuvanog mleka, koji su stvarali enterotoksine) dokazano je prisustvo sea, i kod 24 izolata pored sea gena dokazan je i seb. Nijedan izolat nije imao gene za sintezu C (SEC), D (SED) i E (SEE). Od 26 uzoraka sireva pozitivnih na prisustvo enterotoksogenih koagulaza pozitivnih stafilokoka,enterotoksin je dokazan u 2 (7,69%) uzorka kiselo-koagulišućeg sira u kojima je broj enterotoksogenih koagulaza pozitivnih stafilokoka bio više od 5 log CFU g-1. U kiselo-koagulišućim sirevima u kojima je broj koagulaza pozitivnih stafilokoka veći od 5 log CFU g-1 i pH viši od 5, enterotoksin može biti prisutan u količini dovoljnoj da izazove intoksikaciju.