Abstract
In this research, our aim was to assess the occurrence of Staphylococcus aureus in a Hungarian large-scale dairy farm during the S. aureus control program conducted in the course of our studies. Furthermore, the phenotypic and genotypic properties of the isolates (type of haemolysis, antibiotic susceptibility, staphylococcal enterotoxin (SE) gene carrying ability and spa type) were determined. S. aureus was detected in all bulk tank milk samples collected during this study. Two different spa types were identified among the 17 strains isolated in the farm. A total of 14 of the 17 studied strains (82%) showed β-haemolysis on blood agar, 2/17 strains (12%) expressed double zone and 1/17 strains (6%) showed weak β-haemolysis. All strains were susceptible to most antibiotics tested (cefoxitin, chloramphenicol, clindamycin, erythromycin, gentamicin, tetracycline and trimethoprim/sulphamethoxazole), but all strains were resistant to penicillin G. A total of 11 of the 17 strains (65%) were found to harbour seg, sei, selm, seln, selo genes; 4/17 strains (24%) harboured sei, selm, seln, selo genes and 2/17 strains (11%) harboured sei gene. Since the new SEs/SEls can also cause foodborne outbreaks potentially and all strains were found to be resistant to penicillin G, it is essential to decrease and keep the prevalence of S. aureus low in the dairy farm and the implementation of the S. aureus control program is also highly justified. The results showed that the S. aureus count decreased by the end of our studies, so the control program was proved to be effective.
Highlights
In this study the S. aureus count in the samples collected during the sixth sampling was lower (p < 0.05) than in the samples collected during all the other sampling occasions, including the first sampling (3.1 log10 cfu/mL), which was performed in winter (February)
All the strains were found to harbour at least one of these genes; it is essential in the dairy farm to decrease the occurrence and keep the prevalence of S. aureus low, and the implementation of the S. aureus control program is highly justified, as well
The results show that the mean S. aureus count decreased by the end of the year, and the amounts did not exceed the refusal limit in the case of the last two samplings
Summary
53 validly published species and 24 subspecies can be distinguished within the genus Staphylococcus [1]. Staphylococcus aureus is one of the most common pathogens associated with contamination of raw milk and dairy products [2]. Staphylococcus spp. are spherical, non-spore-forming Gram-positive bacteria that are facultative anaerobes [3]. Contamination of raw milk with S. aureus can occur in the dairy farm, for example, from the skin, mucous membranes of dairy animals, milking equipment, milkers’ hands, or the milking parlour environment [4]
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