A new strain of methicillin-resistant Staphylococcus aureus (MRSA) has been identified in both humans and dairy cows.
Scientists at the University of Cambridge made the discovery while researching the S. aureus bacterium, which causes an infection in cows' udders called bovine mastitis.
They say that the new strain, which is documented in the Lancet Infectious Diseases journal, only accounts for a small proportion of all MRSA infections, but that numbers appear to be on the increase.
It cannot be detected by tests currently used to identify MRSA, as it is genetically very different to previous strains.
First author Dr Laura Garcia-Alvarez, from the University of Cambridge's Veterinary School, said: 'To find the same new strain in both humans and cows is certainly worrying. However, pasteurisation of milk will prevent any risk of infection via the food chain.
'Workers on dairy farms may be at higher risk of carrying MRSA, but we do not yet know if this translates into a higher risk of infection.'
A Food Standards Agency spokesman told the Daily Mail that the risk of contracting the new strain of MRSA through cow's milk is 'extremely low', as most milk is pasteurised.