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

OBJECTIVES

The objective of this collaborative surveillance project was to investigate the prevalence of methicillin-resistant Staphylococcus aureus (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 and 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 of 149 (75.8%) pig farms, MRSA was present. The prevalence was lower among veal calf (44/173; 25.4%), and dairy (11/181; 6.1%), sheep (7/156; 4.5%), and broiler 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 analysed 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 a 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 the MRSA belonged to GG0398 confirming the continuous predominance of this type of MRSA in livestock and on meat.

Livestock-associated methicillin-resistant Staphylococcus aureus: Establishing links between animals and humans on livestock holdings

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) represents a concern in both human and veterinary medicine. The aim of this study was to investigate potential LA-MRSA transmission between animals and humans in rural settings. To this aim, a study was designed to include 14 farms in Slovenia, which were selected on the basis of a farmer (initial patient) with confirmed LA-MRSA infection and regular animal contacts. On all farms, the initial patients, their household members, animals and barn environment were analysed for the presence of LA-MRSA. In addition, the epidemiologically linked hospital-related LA-MRSA isolates were included to investigate possible nosocomial transmissions. On five farms, LA-MRSA was discovered both in animals and in humans. In total, 49 LA-MRSA isolates of different origins underwent whole-genome sequencing, antimicrobial susceptibility testing and spa typing. All 49 isolates belonged to the sequence type 398 (ST398), spa types t011 and t034, and harboured staphylococcal chromosomal cassette mec Vc. High levels of concordance between resistance phenotypes and genotypes were observed. No transmission pairs between animals and initial patients were discovered. However, several isolates originating from farm animals and other household members formed clusters with pairwise distances of ≤14 single nucleotide polymorphisms (SNPs), indicating recent transmission events. In addition, three closely related isolates (0 SNP) form hospitalized patients were observed, indicating a possible nosocomial transmission. Two hospital-related isolates harboured the immune evasion cluster genes, which are associated with adaptation to the human host; however, these two isolates differed in >30 SNPs from the remaining isolates. Characteristics of LA-MRSA from Slovenia reflect those observed previously in other European studies. Immune evasion cluster-positive LA-MRSA ST398 suggests its re-adaptation to the human host and calls for a closer monitoring of such emerging LA-MRSA lineages, in addition to monitoring and preventing the introduction of LA-MRSA from farms to hospitals where transmission is highly plausible.