Low occurrence of safety hazards in coagulase negative staphylococci isolated from fermented foodstuffs

Abstract

Some coagulase negative staphylococci (CNS) species play an important role in the fermentation of meat and milk products and are considered as food-grade. However, the increasing clinical significance of CNS and the presence of undesirable and unsafe properties in CNS question their presence or use in food. Our goal was to assess the safety of CNS by developing a diagnostic microarray targeting 268 genes corresponding to safety hazards in a food context i.e. toxins (especially enterotoxins) and determinants of antibiotic resistance and biogenic amine production. Target genes were selected among staphylococci and Gram-positive species that may be in contact with CNS in foodstuffs. The diagnostic microarray was used to screen 129 strains belonging to the 2 dominant species isolated from foodstuffs (S. equorum and S. xylosus) and the 2 main species isolated both in foodstuffs and clinical samples (S. epidermidis and S. saprophyticus). Microarray data were further completed by antibiograms and measurement of biogenic amine production. Safety hazards associated with CNS were mostly limited to the presence of antibiotic resistance. Seventy-one percent of the strains possessed at least one gene encoding antibiotic resistance, while only one strain carried an enterotoxin gene. Most strains did not carry any genes encoding staphylococcal toxins (68%), non-staphylococcal toxins (95%) or decarboxylases involved in biogenic amine production (78%). Food safety hazards were more pronounced in S. epidermidis than in the three other species regardless the food or clinical origin of the strains. Seventy-six percent of the strains carrying genes encoding staphylococcal toxin and 69% of strains carrying 5 or more antibiotic determinants belonged to S. epidermidis species. The dominant antibiotic resistance targeted erythromycin, tetracycline and penicillin and were generally traced back to the presence of tetK and blaZ in the two latest cases. Six percent of the food-related strains produced significant amounts of biogenic amines in vitro without any of the corresponding genes detected, reflecting a lack of knowledge on genetic determinants of such production in staphylococci. This work gives a first picture of safety hazards within four species of CNS frequently isolated from food or clinical environment.