Novel homologue meticillin-resistant Staphylococcus aureus

January 01, 0001

Novel homologue meticillin-resistant Staphylococcus aureus

Animals can act as a reservoir and source for the emergence of novel meticillin-resistant Staphylococcus aureus (MRSA) clones in human beings. Here, the researchers from the UK and Denmark 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. 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, the researchers searched for mecA PCR-negative bovine and human S aureus isolates showing phenotypic meticillin resistance. They used whole- genome sequencing to establish the genetic basis for the observed antibiotic resistance.

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.

The researchers concluded: "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."

An important issue regarding antibiotic resistant bacteria.

For the full abstract, click here.

The Lancet Infectious Diseases published online 3 June 2011 © 2011 Elsevier Limited
Meticillin-resistant Staphylococcus aureus with a novel mecA homologue in human and bovine populations in the UK and Denmark: a descriptive study. Laura García-Álvarez, Matthew TG Holden, Heather Lindsay et al. Correspondence to Mark Holmes: [email protected]

Category: T. Endocrine/Metabolic/Nutritional. Keywords: meticillin, resistant, Staphlococcus aureus, novel, homologue, human, bovine, populations, UK, Denmark, descriptive study, journal watch.
Synopsis edited by Dr Stephen Wilkinson, Melbourne, Australia. Posted on Global Family Doctor 17 June 2011

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