Although coagulase-positive staphylococci are considered to be the main factor responsible for food poisoning, an increasing role for the coagulase-negative staphylococci in the production of enterotoxins has been observed in recent years. This study was conducted to assess the occurrence of genes responsible for the production of staphylococcal enterotoxins (SE), enterotoxin-like toxins (SEI) and toxic shock syndrome toxin-1 (TSST-1) in coagulase-negative staphylococci (CoNS) isolated from ready-to-eat food from bars and restaurants. One hundred and eighteen CoNS strains were tested using polymerase chain reaction (PCR) to five superantigenic toxin genes, including five different types of classical enterotoxins (sea, seb, sec, sed and see) and the toxic shock syndrome toxin-1 (tsst-1) as well as to supertoxin-like genes. PCR-positive isolates were then tested using immunoenzymatic methods (SET-RPLA, Vidas SET 2) for toxin expression. Out of 118 CoNS strains, the presence of staphylococcal enterotoxins was confirmed in 72% of them. The most frequently found enterotoxin-like genotype was ser, selu. Two of the tested strains had up to ten different enterotoxin genes in the genome at the same time. Although no production of enterotoxins was detected in the CoNS, which means that their possible role in the epidemiology of food-borne diseases is minimal, the data demonstrated that the toxigenic capacity of the CoNS should not be ignored, and that this group of microorganisms should be continuously monitored in food.

The capacity for biofilm formation is one of the crucial factors of staphylococcal virulence. The occurrence of biofilm-forming staphylococci in raw milk may result in disturbances in technological processes in dairy factories as well as the contamination of finished food products. Therefore, this study aimed to determine the prevalence and characteristics of staphylococcal biofilm formation in raw milk samples and to explore the genetic background associated with biofilm formation in those isolates. The material subjected to testing included 30 cow’s milk samples acquired from farms in the central part of Poland. A total of 54 staphylococcal strains were isolated from the samples, of which 42 were classified as coagulase-negative (CoNS) staphylococci belonging to the following species: S. haemolyticus, S. simulans, S. warneri, S. chromogenes, S. hominis, S. sciuri, S. capitis, S. xylosus and S. saprophyticus, while 12 were classified as S. aureus. The study examined the isolates’ capacity for biofilm formation and the staphylococcal capacity for slime production and determined the presence of genetic determinants responsible for biofilm formation, i.e., the icaA, icaD, bap and eno and, additionally, among coagulase-negative staphylococci, i.e., the aap, bhp, fbe, embP and atlE. Each tested isolate exhibited the capacity for biofilm formation, of which most of them (79.6%) were capable of forming a strong biofilm, while 5.6% formed a moderate biofilm, and 14.8% a weak biofilm. A capacity for slime production was demonstrated in 51.9% isolates. Most of the tested staphylococcal strains (90.7%) had at least one of the tested genes. Nearly half (47.6%) of the CoNS had the eno gene, while for S. aureus, the eno gene was demonstrated in 58.3% isolates. The frequency of the bap gene occurrence was 23.8% and 25% in CoNS strains and S. aureus, respectively. The fbe gene was demonstrated in only three CoNS isolates. The presence of the icaA was only demonstrated in CoNS strains (24.1%), while the icaD was found in both CoNS strains (21.4%) and S. aureus (100%). Among the CoNS, the presence of the embP (16.7%), aap (28.6%) and atlE (23.8%) was demonstrated as well. The obtained study results indicate that bacteria of the Staphylococcus spp. genus have a strong potential to form a biofilm, which may pose a hazard to consumer health.

The findings of this study indicate that Enterococcus isolated from ready-to-eat food is able to horizontally transfer genes encoding various antibiotic resistance mechanisms. © 2018 Society of Chemical Industry.

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Cheeses produced from unpasteurized milk by traditional production methods may contain many groups of microorganisms, including Staphylococcus aureus. The aim of this study was to determine the occurrence of S. aureus in the artisanal cheese production chain from unpasteurized milk. We investigated the prevalence of S. aureus strains isolated from various stages of artisanal cheese of unpasteurized milk production from farms in the northeastern and southern parts of Poland and characterized them. Characterization included antimicrobial susceptibility by microbroth dilution and biofilm formation by in vitro assay. Among all strains, the presence of enterotoxigenic genes and genes involved with biofilm formation and antibiotic resistance were screened by PCR-based methods. A total of 180 samples were examined. A high percentage of strains were resistant to penicillin (54/58.1%) and tobramycin (32/34.4%). Some tested isolates also showed resistance to the macrolide class of antibiotics: azithromycin, clarithromycin, and erythromycin at 17/18.3%, 15/16.1%, and 21/22.6%, respectively. Among tested isolates, we also found phenotypic resistance to oxacillin (9/9.7%) and cefoxitin (12/12.9%). The blaZ gene encoding penicillin resistance was the most common gene encoding antibiotic resistance among the tested strains. All isolates showing phenotypic resistance to cefoxitin possessed the mecA gene. The study also evaluated the prevalence of biofilm-associated genes, with eno the most frequently associated gene. Eighty-nine out of 93 S. aureus isolates (95.7%) possessed at least one enterotoxin-encoding gene. The results of this study showed that production of raw milk cheeses may be a source of antibiotic resistance and virulent S. aureus. Our results suggest that artisanal cheese producers should better control production hygiene.