New MRSA Strain Detected in Cow's Milk

Variant is genetically different from existing strains

FRIDAY, June 3 (HealthDay News) -- Researchers have identified a novel methicillin-resistant Staphylococcus aureus (MRSA) strain in cow's milk that is genetically different from existing MRSA strains; their research has been published online June 3 in The Lancet Infectious Diseases.

Laura Garcia-Alvarez, Ph.D., of the University of Cambridge in the United Kingdom, and colleagues obtained isolates of bovine MRSA from the Veterinary Laboratories Agency in the United Kingdom, and isolates of human MRSA from diagnostic or reference laboratories (two in the United Kingdom and one in Denmark). The investigators assessed phenotypic resistance and used whole genome sequencing to establish the genetic basis for antibiotic resistance.

The investigators found a MRSA strain with a new mecA gene that was not detected by the standard confirmatory tests for mecA, including polymerase chain reaction or monoclonal antibody methods. The investigators also found indirect evidence that cows could serve as an important reservoir of this new variant of MRSA infection in humans.

"Such evidence suggests that a bovine reservoir exists, from which mecALGA251 MRSA is transmitted to people," the authors write. "The discovery of this previously undetected mecA homologue is potentially of public health importance. Diagnostic protocols, whether for clinical or epidemiological purposes, should consider the ramifications of not detecting S. aureus strains that carry this new mecA homologue."

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