Staphylococcus aureus is a very important pathogen for dairy farms and milk processing plants. Subclinical mastitis is often caused by this species, and it can contaminate bulk tank milk when milking cows are suffering from mastitis. Additionally, thermostable enterotoxins (SE) produced by some types of this bacterium can cause food poisoning.<...br>The aim of our research was to examine the number of S. aureus in bulk tank milk in two dairy farms and the enterotoxin-producing ability, genetic relation (pulsotype) and antibiotic resistance of S. aureus strains from different sources (bulk tank milk, udder quarter milk and environment).
The results show that the mean number of S. aureus of bulk tank milk of two farms significantly differed (P<0.05). Fourteen isolates were selected for further molecular genetic studies (five isolates were from bulk tank milk and nine isolates were from udder quarter milk). S. aureus was not recovered from the environmental samples. Three of the fourteen isolates (21.4%) tested by multiplex PCR were positive for SE genes. Two isolates carried one gene (seb) and one isolate carried two genes (seg and sei). The fourteen strains were classified into three pulsotypes and two subtypes at 86% similarity level. Isolates from bulk tank milk (n=5), were divided into 2 pulsotypes (A, C) and one subtype (C1). The isolates from udder quarter milk (n=9) belonged to three different pulsotypes (A, B, C) and two subtypes (A1, C1). The distribution of pulsotypes in the present study revealed genetic relationship between S. aureus isolated from udder quarter milk and bulk tank milk. This could be explained by the fact that in farms with a high number of infected cows, these cows could represent the main source of contamination. The results of the antibiotic resistance investigations show, that all strains were susceptible to methicillin, cefoxitin, lincomycin, tetracycline, erythromycin and sulfamethoxazole/trimethoprim. Thirteen out of fourteen strains were resistant to penicillin (A and C pulsotypes, A1 and C1 subtypes) and just one isolate was susceptible (B pulsotype) to all antibiotics tested.
For dairy farms, it is of great importance to insure the appropriate hygienic status of milk and to examine it regularly. Escherichia coli, belonging to the coliform bacteria type of, is a good indicator of contamination, and therefore suitable for characterising the hygienic condition of milk production.
The aim of our research was to exami
Analysing the connection between the E. coli count and the farm size we found no significant difference between the farms. On the basis of the mean values of the E. coli count, we can say that the hygienic conditions are appropriate for mid-sized farms, and tolerable for large farms. We found differences in the hygienic status among the small farms. Half of the eight small farms, had no adequate hygiene. The results of the analysis of the quality categories show that the probability of inadequate quality milk was the largest on small farms (37.5%).
Comparing the various housing and milking methods with each other, there were numerical differences in the E. coli count, but these differences were not significant. We got higher E. coli count values on those farms using tied stall barn and bucket milking installation. The reason for this could be that in cases of farms using bucket milking installation, it is harder to meet the requirements.
After forming groups by farm size, housing and milking methods, we found that the E. coli counts are adequate on mid-size farms using various housing and milking methods; and tolerable on those large farms using loose housing stable and a milking parlour. At the same time, we found inadequate E. coli counts on the smaller farms using tied stall barns and bucket milking installation.
The results show that if there is suitable attention, independent of farm size, housing and milking procedure, it is possible to produce milk with low E. coli counts, and to insure appropriate hygienic conditions.
Further detailed examinations are needed to decide which factors of housing and milking technologies influence the E. coli count of bulk tank milk.