A new strain of methicillin-resistant Staphylococcus aureus (MRSA) occurring in human and dairy cows has been identified in Europe (Garcia-Alvarez L et al. Lancet Infect
Dis. doi:10.1016/S1473-3099(11)70126-8 [published online ahead of print June 3, 2011]).
Researchers in the United Kingdom isolated the novel strain in milk from sick cows. The antibiotic growth test revealed the novel MRSA strain; standard molecular tests that work by identifying the presence of the gene, mecA, which is responsible for methicillin resistance, did not detect it. Sequencing the genome of the new strain revealed that it carried a much altered form of the mecA gene, allowing it to elude standard molecular tests.
Friedrich MJ. New MRSA Strain. JAMA. 2011;306(3):257. doi:10.1001/jama.2011.964