Occurrence and antimicrobial resistance of Staphylococcus aureus in bulk tank milk and milk filters

This work is focused on the monitoring of Staphylococcus aureus prevalence in raw milk and milk filters, its antibiotic resistance and detection of methicillin resistant Staphylococcus aureus (MRSA). Samples of raw cow´s milk and milk filters were collected in the period from 2012 till 2014, from 50 dairy farms in the Czech Republic. The total of 261 samples (164 samples of raw milk and 97 milk filters) were cultivated on Baird-Parker agar. Both the typical and atypical colonies were examined by plasmacoagulase test and PCR method was used for detection of species specific fragment SA442 and mec A gene. Standard disk diffusion method was used to determinate resistance to antimicrobial agents. The bacterium Staphylococcus aureus was detected on 25 farms (50%). The antimicrobial resistance showed differences between the farms. Total of 58 samples were positive for Staphylococcus aureus , of which were 37 (14.2%) isolated from raw milk samples and 21 (8.1%) from milk filters. From these samples we isolated 62 Staphylococcus aureus strains, 41 isolates bacteria S. aureus from raw milk (66.1%) and 21 isolates S. aureus from milk filters (33.9%). The presence of antibiotic resistance in  Staphylococcus aureus isolates was low, most of them were resistant to amoxicilin. According to the results obtained by the PCR method for the methicillin - resistant S. aureus (MRSA), the mec A gene was present in 6 strains (9.7%), 4 isolates obtained from milk samples (6.5%) and 2 isolates from milk filters (3.2%).  These isolates can be considered as a possible source of resistance genes, which can be spread through the food chain. Nowadays, a globally unfavourable increasing trend of prevalence of methicillin resistant staphylococci strains especially Staphylococcus aureus is being observed worldwide. The improper hygiene and poor farm management practices contributed to the presence of S. aureus in the milk. This may have contributed to the high level of S. aureus isolated. Improving the hygienic conditions of the milking environment and utensils may reduce the prevalence of S. aureus in milk. Objective of this study was monitoring of Staphylococcus aureus prevalence and determine the prevalence rate of antimicrobial resistance of S. aureus isolated from raw milk and milk filters in the Czech Republic.