TDK conference 2019

Staphylococcus aureus (SA) causes an array of infections in humans and in economically important livestock animals. At the same time SA mastitis is a major economic burden on the global dairy industry. Since first documented in 1972, livestock associated (LA-)MRSA of clinical and subclinical mastitis origin has been reported from numerous countries across Europe. Some genetic variants of MRSA have the potential to switch host species and colonise or even cause infection in the new host. As MRSA may also enter the food-chain and sporadically can be isolated from retail dairy products, consequently – depending on the genotype – it poses risk to human health as well. Due to lack of data, the occurrence and risk of LA-MRSA of dairy origin in Hungary can only be assumed.

To elucidate prevalence and genetic variability of MRSA in dairy production, we performed both retrospective and prospective investigations in the frame of a recently started monitoring programme. First, we analysed the conserved bovine MRSA isolates of the Veterinary Diagnostic Directorate (VDD), Budapest from the past 15 years. Secondly, we screened 455 individual SA isolates of milk origin by PCR between July 2017 and July 2018 provided by two milk-hygiene laboratories. Detailed characterisation of both conserved and newly recovered MRSA isolates was carried out by means of selected molecular biological methods (spa-typing, MLST, SCCmec-typing) and by antimicrobial susceptibility testing. Results were evaluated regarding the supplementary data of the isolates.

Between 2003 and 2018 overall 26 MRSA strains originating from 10 dairy farms have been deposited in the culture collection of the VDD. In case of two farms, isolates of the ST1-t127-IV genotype occurred several times causing subclinical mastitis outbreaks. From other farms variable genotypes were registered sporadically. The screening of 455 individual SA isolates originating from 33 dairy farms resulted in only 4 MRSA strains. The 4 strains originated from 3 farms and all of them belonged to the ST398 sequence type. Resistance to ciprofloxacin, clindamycin, streptomycin and tetracycline is common among the examined isolates, while phenotypic resistance to different antimicrobials of human medical interest seems to be rare.

Although MRSA of milk origin has appeared to be sporadic in Hungary in the past 15 years, some cases raise the possibility of mastitis outbreaks caused by specific genotypes of the pathogen. At the same time genotypes with low host specificity, like ST1 and ST398 may also occur and, according to previous reports, they can colonise humans as well, posing occupational hazard to dairy workers and veterinarians. The wide spectrum of antimicrobial resistance in most of the examined MRSA strains of milk origin highlights the role of animal breeding as a possible source of microbial resistance genes.