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Genome analysis of methicillin resistance in Macrococcus caseolyticus from dairy cattle in England and Wales

Alison C MacFadyen1, Elizabeth A Fisher2, Ben Costa2

  • 11​Royal (Dick) School of Veterinary Studies and The Roslin Institute, University of Edinburgh, Edinburgh, UK.

Microbial Genomics
|June 20, 2018
PubMed

Insights

Methicillin-resistant Macrococcus caseolyticus, a potential veterinary pathogen, was found in UK milk. These bacteria carry mecB or mecD genes, contributing to the spread of antibiotic resistance in animals.

Area of Science:

  • Veterinary Microbiology
  • Antimicrobial Resistance
  • Molecular Epidemiology

Background:

  • Macrococcus species are common in animals but increasingly recognized as veterinary pathogens.
  • These bacteria can carry methicillin resistance genes, potentially spreading them to more harmful staphylococci.
  • Methicillin-resistant Macrococcus caseolyticus (MRM) poses a growing concern in animal health.

Purpose of the Study:

  • To identify and characterize methicillin-resistant Macrococcus caseolyticus (MRM) from bovine milk in England and Wales.
  • To investigate the molecular epidemiology and genetic basis of methicillin resistance in these isolates.
  • To assess the prevalence and distribution of MRM in the UK dairy sector.

Main Methods:

  • Isolation and antimicrobial susceptibility testing (Vitek2, disc diffusion, Etest) of Macrococcus caseolyticus from bovine bulk tank milk.
  • Whole-genome sequencing to determine phylogenetic relationships and identify methicillin resistance genes (mecA-D).
  • Phenotypic confirmation of methicillin resistance using cefoxitin disc diffusion and Etest.

Main Results:

  • 33 methicillin-resistant Macrococcus caseolyticus isolates were identified.
  • Twenty-seven isolates carried the mecD gene, and six carried the mecB gene; mecA and mecC were absent.
  • Phylogenetic analysis revealed a heterogeneous population of MRM with a wide geographical distribution.
  • All isolates showed phenotypic resistance to methicillin, though only one was flagged by the Vitek2 cefoxitin screen.

Conclusions:

  • Methicillin-resistant Macrococcus caseolyticus is present in bovine milk in England and Wales, carrying diverse resistance genes (mecB, mecD).
  • The heterogeneous nature and widespread distribution of these isolates highlight their potential role in the spread of antimicrobial resistance.
  • Increased awareness and epidemiological study are needed for veterinary microbiology laboratories to manage MRM effectively.
Keywords:
macrococcimec genesmethicillin resistancestaphylococciveterinary microbiology

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