A new strain of methicillin-resistant Staphylococcus aureus (MRSA) that occurs both in human and dairy cow populations has been identified by researchers at the University of Cambridge.

The scientists discovered the antibiotic resistant strain while researching S. aureus, a bacterium known to cause bovine mastitis. When they attempted to use the standard molecular tests identifying the presence of the gene responsible for methicillin resistance (the mecA gene), the tests came back negative for MRSA.

The researchers subsequently sequenced the entire genome (decoding all of the genes in the bacteria’s DNA) and realized that the new strain possessed unconventional DNA for MRSA.  They found that the new strain had a mecA gene, but with only 60% similarity to the original mecA gene.

Subsequent research revealed that the new strain was also present in humans. During the study, the new strain was found in samples from Scotland, England, and Denmark (some from screening tests and others from people with MRSA disease). It has since been identified in Ireland and Germany.

Laura García-Álvarez, et al., Meticillin-resistant Staphylococcus aureus with a novel mecA homologue in human and bovine populations in the UK and Denmark: a descriptive study, The Lancet Infectious Diseases, 2011; [DOI:10.1016/S1473-3099(11)70126-8]