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

Cheng Cui,Mark A Holmes,Xiaoliang Ba

doi:10.1093/jacamr/dlaa125

Abstract

ObjectivesTo evaluate the current prevalence status of mecC MRSA among dairy farms in England and Wales 5 years after a previous survey conducted in 2011–12.MethodsA 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® 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.ConclusionsThese 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.

Highlights

MRSA represent a significant healthcare problem causing infections in both people and animals
The mecC gene was initially found among bovine and human isolates from the UK and Denmark in 2011.2 mecC MRSA was first isolated from cattle and humans, it has a wide range of host species, including other livestock species, companion animals and wildlife.[3]
Agglutination assays for mecA encoded PBP2a will misidentify mecC MRSA as being susceptible.[4]

Summary

Introduction

MRSA represent a significant healthcare problem causing infections in both people and animals. The resistance to b-lactams in staphylococci most commonly results from expression of a blaZ gene (encoding a b-lactamase) and/or a mec gene (mecA, mecC or mecB encoding an alternative PBP2, the target of b-lactams).[1]. MecC MRSA test negative when using molecular detection methods based on the mecA gene. Agglutination assays for mecA encoded PBP2a (using latex beads coated with monoclonal antibodies) will misidentify mecC MRSA as being susceptible.[4] A number of PCR assays[5] have been developed or adapted to include detection of the mecC gene. Phenotypic testing for MRSA based on antimicrobial susceptibility fails to discriminate between mecA and mecC MRSA and severe and fatal cases of mecC MRSA infections have been described in the literature.[6]

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