Prevalence and characterization of mecC MRSA in bovine bulk tank milk in Great Britain, 2017-18

Objectives: To evaluate the current prevalence status of mecC MRSA among dairy farms in England and Wales 5years after a previous survey conducted in 2011-12. Methods: A convenience sample of 697 dairy farms in England and Wales was used for the study, conducted in 2017-18, testing bulk tank milk samples for the presence of mecC MRSA using high salt broth enrichment and chromogenic MRSA agar selection. All putative MRSA isolates were screened by PCR for the presence of mecA and mecC genes and subjected to antimicrobial susceptibility testing using both the disc diffusion method and VITEK (R) 2. MRSA isolates were also sequenced for genomic characterization. Results: mecC MRSA were detected on 4 out of 697 dairy farms in England and Wales (prevalence 0.57%, 95% CI 0.16%-1.46%). Three of the mecC isolates were ST425 and one was ST4652 (in the CC130 lineage). Two mecA MRSA were also isolated: one ST5 and one ST398. Conclusions: These results indicate that there has been a substantial reduction in the prevalence of mecC MRSA in England and Wales with a 72% reduction (2.15% to 0.57%) compared with a previous study. While the levels of mecA MRSA remain very low the continued presence of ST398, a livestock-associated MRSA, suggests that this lineage is established in the UK.

Automated summary

The study found that mecC MRSA prevalence on dairy farms in England and Wales was 0.57%, with a 72% reduction compared to a previous study. While mecA MRSA levels remained low, the presence of ST398 indicates its establishment in the UK.