Differentiation of toxigenic Staphylococcus aureus strains isolated from retail meat products

Staphylococcus aureus is a saprophyte and commensal of the skin and mucous membranes in both animals and humans. As a pathogen, it can cause a number of diseases ranging from minor skin infections to fatal sepsis. Toxigenic strains of S. aureus are currently among the leading causes of food-borne intoxication (staphylococcal enterotoxicosis). Food contamination sources can be humans, raw materials, environment, technological equipment, etc. The identification of the origin of S. aureus would be helpful in the detection of the sources and routes of contamination. The aim of our study was to determine the probable origin of the selected S. aureus isolates coming from retail meat products intended for direct consumption with the use of phenotypic and genotypic methods. A set of 45 S. aureus isolates producing staphylococcal enterotoxins (SEs) with the potential to cause food-borne intoxication were selected for the study. These isolates were producers of the following enterotoxins: SEA (n = 10), SEB (n = 8), SEC (n = 10), SED (n = 7), SEH (n = 9), and SEB along with SED (n = 1). The phenotypic method used was based on the assessment of the growth on crystal violet agar (CV agar). A PCR-based genotypic method enabled the screening of the isolates for the sak gene encoding the enzyme staphylokinase typically found in human S. aureus isolates. As can be inferred from the type of growth on CV agar and the presence of the sak gene, all the isolates analysed were probably of human origin. These results confirm that humans are a major source of the bacteria S. aureus in both the food industry and retail sale of food products.