Biotype characterization of Staphylococcus aureus isolated from milk and dairy products of private production in the western regions of Ukraine

Abstract

Prevention of foodborne diseases is a priority for the world health system. In the process of manufacturing milk and dairy products, the most important factor compromising their safety is seeding with a conditionally pathogenic and pathogenic microflora. Salmonella, Escherichia coli, Listeria and other microorganisms that reproduce in dairy products without changing their organoleptic properties are a particular danger. Staphylococcus aureus is an opportunistic, conditionally pathogenic microorganism that often contaminates raw milk and dairy products. The aim of the research presented in this article was to determine the dissemination of S. aureus in milk and milk products of household production in the western regions of Ukraine, to identify the biotypes of S. aureus, production of enterotoxins and the presence of methicillin-resistant strains. S. aureus was isolated on BD Baird-Parker Agar. The biotypes of S. aureus were determined according to Meer. The determination of MRSA was carried out on the chromogenic Agar chromID MRSA ("Biomerioux", Russia). The mecA gene was determined using the LightCycler MRSA Advanced Test with LightCycler 2.0 primer (Roche Molecular Biochemicals, Germany). To determine staphylococcal enterotoxins, the test system RIDASCREENSET A, B, C, D, E (R-Biopharm AG, Darmstadt, Germany) was used. We isolated saprophyte staphylococci from milk of raw and dairy products in western regions of Ukraine in 82.7–97.4% of samples. S. aureus is much more rarely isolated from these dairy products, so it was isolated from sour cream at 62.8 ± 0.9%, from milk at 35.5 ± 1.3% and cottage cheese at 23.0 ± 1.6%. Of the most well known biotypes of S. aureus present in milk of raw and dairy products of domestic production, two ecological types were distinguished: human and cattle. In this case S. aureus var. hominis was isolated more often than in S. aureus var. bovis. This gives grounds to believe that the main source of contamination with milk staphylococci of raw and dairy products of domestic production is people. Enterotoxin type A, which causes foodborne toxemia, was produced by S. aureus in 40.0 ± 0.5% of cases. Consequently, home-produced dairy products can spread staphylococcal toxicity caused by S. aureus var. hominis. It was found that 17.8 ± 0.6% of S. aureus var. hominis were resistant to methicillin, which is 1.8 times greater than that of S. aureus var. bovis. This gives grounds to consider that there is a risk of MRSA infection to consumers of home-produced dairy products. All methicillin-resistant staphylococci studied produced enterotoxins.

Keywords

• staphylococci
• biotypes
• MRSA
• enterotoxins