Meticillin-resistant Staphylococcus aureus with a novel mecA homologue in human and bovine populations in the UK and Denmark: a descriptive study

Laura Garcia-Alvarez, Matthew Thomas Geoffrey Holden, Heather Lindsay, Cerian R. Webb, Derek F. J. Brown, Martin D. Curran, Enid Walpole, Karen Brooks, Derek J. Pickard, Christopher Teale, Julian Parkhill, Stephen D. Bentley, Giles F. Edwards, E. Kirsty Girvan, Angela M. Kearns, Bruno Pichon, Robert L. R. Hill, Anders Rhod Larsen, Robert L. Skov, Sharon J. PeacockDuncan J. Maskell, Mark A. Holmes*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

596 Citations (Scopus)

Abstract

Background Animals can act as a reservoir and source for the emergence of novel meticillin-resistant Staphylococcus aureus (MRSA) clones in human beings. Here, we report the discovery of a strain of S aureus (LGA251) isolated from bulk milk that was phenotypically resistant to meticillin but tested negative for the mecA gene and a preliminary investigation of the extent to which such strains are present in bovine and human populations.

Methods Isolates of bovine MRSA were obtained from the Veterinary Laboratories Agency in the UK, and isolates of human MRSA were obtained from diagnostic or reference laboratories (two in the UK and one in Denmark). From these collections, we searched for mecA PCR-negative bovine and human S aureus isolates showing phenotypic meticillin resistance. We used whole-genome sequencing to establish the genetic basis for the observed antibiotic resistance.

Findings A divergent mecA homologue (mecA(LGA251)) was discovered in the LGA251 genome located in a novel staphylococcal cassette chromosome mec element, designated type-XI SCCmec. The mecA(LGA251) was 70% identical to S aureus mecA homologues and was initially detected in 15 S aureus isolates from dairy cattle in England. These isolates were from three different multilocus sequence type lineages (CC130, CC705, and ST425); spa type t843 (associated with CC130) was identified in 60% of bovine isolates. When human mecA-negative MRSA isolates were tested, the mecA(LGA251) homologue was identified in 12 of 16 isolates from Scotland, 15 of 26 from England, and 24 of 32 from Denmark. As in cows, t843 was the most common spa type detected in human beings

Interpretation Although routine culture and antimicrobial susceptibility testing will identify S aureus isolates with this novel mecA homologue as meticillin resistant, present confirmatory methods will not identify them as MRSA. New diagnostic guidelines for the detection of MRSA should consider the inclusion of tests for mecA(LGA251).

Original languageEnglish
Pages (from-to)595-603
Number of pages9
JournalLancet Infectious Diseases
Volume11
Issue number8
DOIs
Publication statusPublished - Aug 2011

Keywords

  • CASSETTE CHROMOSOME MEC
  • LIVESTOCK-ASSOCIATED MRSA
  • TIME PCR ASSAY
  • METHICILLIN-RESISTANT
  • RAPID IDENTIFICATION
  • MULTIPLEX PCR
  • PREVALENCE
  • ELEMENT
  • NETHERLANDS
  • GUIDELINES

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