Livestock-associated methicillin-resistant Staphylococcus aureus epidemiology, genetic diversity, and clinical characteristics in an urban region

Methicillin-resistant Staphylococcus aureus GG0398 on livestock farms and meat in the Netherlands

INTRODUCTION

The objective of this collaborative surveillance project was to investigate the prevalence of MRSA among livestock farms, persons working/living on these farms and on meat.

METHODS

Samples from Dutch broiler-, pig-, veal calf-, dairy cattle- and sheep farms, persons living/working on these farms and retail meat collected between 2018 - 2023 were cultured using (pre-) enrichment and selective plates. Next-generation sequencing of a subset of MRSA was performed to detect mecA/mecC, Panton-Valentine leucocidin (PVL) and to assign genogroups (GGs).

RESULTS

On 113/149 (75.8%) pig farms MRSA was present. The prevalence was lower among veal calf - (44/173; 25.4%), dairy- (11/181; 6.1%), sheep- (7/156; 4.5%), and broilers farms (0/195; 0%). Among 375 persons working/living on the farms, we identified 17 (4.5%) nasal MRSA carriers and all were farmers. All but two isolates from the farms belonged to GG0398 (= CC398). In total, 4529 Dutch retail meat samples were analyzed and 412 (9.1%) were MRSA-positive. Poultry meat was most often contaminated. Most meat isolates (97/148; 65.5%) belonged to GG0398. All but one isolate carried mecA, and all were PVL-negative.

CONCLUSIONS

Despite the reduction of antimicrobial use by >70% in veterinary medicine since 2009, most pig farms are still MRSA positive. Farmers have a higher risk of being nasal MRSA carrier than persons in the general population. Meat is regularly contaminated with MRSA, but this is considered a limited risk for consumers. Almost all MRSA belonged to GG0398 confirming the continuous predominance of this type of MRSA in livestock and on meat.

A look at staphylococci from the one health perspective

Staphylococcus aureus and other staphylococcal species are resident and transient multihost colonizers as well as conditional pathogens. Especially S. aureus represents an excellent model bacterium for the "One Health" concept because of its dynamics at the human-animal interface and versatility with respect to host adaptation. The development of antimicrobial resistance plays another integral part. This overview will focus on studies at the human-animal interface with respect to livestock farming and to companion animals, as well as on staphylococci in wildlife. In this context transmissions of staphylococci and of antimicrobial resistance genes between animals and humans are of particular significance.