S. epidermidis strains from artisanal cheese made from unpasteurized milk in Poland - Genetic characterization of antimicrobial resistance and virulence determinants

Abstract

In Poland artisanal cheese production is an important local economic activity. Artisanal cheese is usually produced using raw cow's milk, animal rennet and salt, without the addition of starter cultures. Coagulase negative staphylococci (CoNS) are often present in artisanal cheeses. Pathogenic potential of some CoNS species, especially S. epidermidis, suggests that they could correspond to emerging pathogens. The identified risk factors correspond to virulence, antibiotic resistance and biofilm formation. Therefore, we aimed to characterize S. epidermidis isolated along the artisanal raw milk production chain. Seventy artisanal cheeses samples from unpasteurized cow milk purchased in Podlasie and Warmia and Mazury region in Poland, were included in this study. A total of 26 S. epidermidis isolates were obtained. Most of them were antimicrobial resistant, such as to penicillin (84,6%), clindamycin (46,2%), tetracycline (42,3%), erythromycin (42,3%) and cefoxitin (26,9%). Only one isolate was susceptible to all antibiotics used in the study. All methicillin resistant S. epidermidis strains (26,9%) harbored mecA gene. Isolates, phenotypic resistant to tetracycline, harbored at least one tetracycline resistance determinant on which tet(M) was most frequent. Moreover, all tetracycline resistant strains harbored Tn916-Tn1545-like integrase family gene. In the erythromycin resistant isolates, the macrolide resistance genes ermC, ermB or msrA/B were present. Seven strains demonstrated a strong ability to form biofilm and moderate and weak biofilm was demonstrated by 4 strains, whereas 11 of S. epidermidis isolates were found to be unable to form a biofilm. All strains producing strong biofilm harbored the icaD gene which occurred independently or in combination with the icaA. Insertion element IS256, was identified in 15,4% of S. epidermidis strains, all of which were multidrug resistant. Arginine Catabolic Mobile Element (ACME) was identified in 13 of the 26 examined strains (50%). Most common was ACME type I (26,9%), followed by type III (15,4%) and type II (7,7%). Our data indicate that S. epidermidis are widely present in artisanal cheeses from raw whole cow milk in Poland. Many isolated strains containing more virulence factors and antibiotic resistant and carry mobile genetic elements which represent a potential source of resistance transmission to bacteria in humans.