Prevalence and molecular characterization of enterotoxin-producing strains of Staphylococcus aureus isolated from Serbian dairy cows

Abstract

Staphylococcus aureus is known worldwide as a frequent cause of mastitis in dairy cattle. Due to the production of heath resistant enterotoxins, this pathogen is also a major cause of food poisoning among humans, with symptoms of often severe vomiting and diarrhea. The aim of our study was to determine the prevalence of enterotoxinproducing strains of S. aureus originating from samples of cows with subclinical and clinical mastitis in the Republic of Serbia. Furthermore, we analyzed the type of staphylococcal enterotoxin they produce and phylogenetic relatedness among the S. aureus isolates recovered from milk in this study. Production of staphylococcal enterotoxins A, B, C, D and E was determined by commercial immunoenzyme assay VIDAS® SET2, and presence of corresponding genes encoding enterotoxin synthesis in positive isolates confirmed by Polymerase Chain Reaction. Enterotoxin production was determined in 5 out of 75 (6.67%) isolates of S. aureus and all of them produced staphylococcal enterotoxins C. After analyzing the nucleotide sequence of the gene encoding the synthesis of staphylococcal protein A, S. aureus isolates were assigned into 2 phylogenetic groups, including 7 clusters. All S. aureus isolates with the presence of sec gene formed one cluster even dough they originated from milk samples from different farms.

Širom sveta S. aureus poznat je kao čest uzročnik mastitisa krava. Takođe predstavlja i glavni uzrok trovanja hranom nakon konzumiranja hrane kontaminirane njegovim enterotoksinima. Cilj ovog istraživanja bio je da se ispita prevalencija enterotoksinprodukujućih sojeva S. aureus poreklom iz vimena krava sa subkliničkim i kliničkim mastitisom u Srbiji, da se odredi tip enterotoksina koji produkuju i da se odredi filogenetska srodnost ovih izolata. Za određivanje sposobnosti sinteze stafilokoknih enterotoksina A, B, C, D i E korišćen je VIDAS® SET2 immunoenzimski test i utvrđeno je da 5 od 75 (6,67%) izolata S. aureus sintetiše enterotoksine. Lančanom reakcijom polimeraze na prisustvo odgovarajućih gena, utvrđeno je da svih 5 izolata poseduju gen za sintezu enterotoksina C. Analizom nukleotidnih sekvenci gena za sintezu stafilokoknog proteina A, izolati S. aureus grupisani su filogenetski u 2 grupe, odnosno u 7 klastera. Svi izolati S. aureus kod kojih je dokazano prisustvo gena za sintezu enterotoksina spadaju u isti klaster.