Anna Zadernowska

This study aimed to genotypic and phenotypic analyses of the enterotoxigenic potential of Staphylococcus spp. isolated from raw milk and raw milk cheeses. The presence of genes encoding staphylococcal enterotoxins (SEs), including the classical enterotoxins (sea-see), non-classical enterotoxins (seg-seu), exfoliative toxins (eta-etd) and toxic shock syndrome toxin-1 (tst-1) were investigated. Isolates positive for classical enterotoxin genes were then tested by SET-RPLA methods for toxin expression. Out of 75 Staphylococcus spp. (19 Staphylococcus aureus and 56 CoNS) isolates from raw milk (49/65.3%) and raw milk cheese samples (26/34.7%), the presence of enterotoxin genes was confirmed in 73 (97.3%) of them. Only one isolate from cheese sample (1.3%) was able to produce enterotoxin (SED). The presence of up to eight different genes encoding enterotoxins was determined simultaneously in the staphylococcal genome. The most common toxin gene combination was sek, eta present in fourteen isolates (18.7%). The tst-1 gene was present in each of the analyzed isolates from cheese samples (26/34.7%). Non-classical enterotoxins were much more frequently identified in the genome of staphylococcal isolates than classical SEs. The current research also showed that genes tagged in S. aureus were also identified in CoNS, and the total number of different genes detected in CoNS was seven times higher than in S. aureus. The obtained results indicate that, in many cases, the presence of a gene in Staphylococcus spp. is not synonymous with the ability of enterotoxins production. The differences in the number of isolates with genes encoding SEs and enterotoxin production may be mainly due to the limit of detection of the toxin production method used. This indicates the need to use high specificity and sensitivity methods for detecting enterotoxin in future studies.

Staphylococcus aureus is one of the most important foodborne pathogens. S. aureus has the capability to produce a variety of toxins, including staphylococcal enterotoxins (SEs). The aim of this study was to evaluate the survival rate of S. aureus cells and analyze enterotoxins gene expression after exposure to osmotic stress and acidic/alkaline stress. To determine survival rates, the traditional plate counting method and flow cytometry were used. The expression levels of the enterotoxin genes were performed by quantitative reverse transcription PCR (RT-qPCR). Expression changes differed depending on the stressors chosen. The obtained results in this study showed the effect of critical food-related stress conditions on SE gene expression in S. aureus. The study showed different expression levels of the tested enterotoxins genes depending on the stress. The most tested enterotoxin genes (seg, sei, and selo) after exposure to pH = 4.5 stress have similar expression as in the optimal condition. After alkaline treatment (pH = 9.6), a similar expression gene value as for the optimal condition was observed. The analysis of gene expression in response to stress caused by NaCl, showed that the expression of selp decreased, whereas selu, selm, and selo genes increased. A significantly decreased expression of the sea gene was observed.