A genetic fingerprint study has provided strong evidence of the MRSA superbug spreading from farm animals to hospitals and baby clinics in the UK.
Scientists identified three samples of the drug-resistant bacteria from a hospital and neonatal unit in Scotland that closely matched a specific strain found in livestock.
Generally, people and animals harbour different forms of the potent MRSA strain CC398 investigated by the researchers.
But the new evidence suggests that the livestock version is capable of being transmitted from animals to humans, and has found its way into hospitals.
Study leader Dr Melissa Ward, from the University of Edinburgh, said: "Our findings emphasise the need for strict biosecurity practices in the food production industry, as well as continued surveillance and infection control of MRSA in hospitals.
"Responsible use of antibiotics in healthcare settings and agriculture is of utmost importance."
MRSA, or methicillin-resistant Staphylococcus aureus, is a serious hazard in hospitals and nursing homes. The CC398 strain is known to cause serious and sometimes life-threatening infections in both humans and animals. In dairy herds, it has been linked to cases of bovine mastitis.
Dr Ward's team unravelled the full genetic codes of British CC398 samples and compared them with published genetic data on the same bugs from humans and livestock around the world.
The research showed that the strain had entered the UK on several occasions since the mid-1940s, but the original source of the bacteria remained unclear.
The most significant evidence of animal-to-human transmission came from three genetic sequences of MRSA collected in Scotland.
Two were from samples taken six months apart from a neonatal ward in the Greater Glasgow and Clyde area. The third was obtained from a cleaning project at a Glasgow hospital.
All three were a genetic match for MRSA CC398 strains in livestock.
Writing in the journal Applied and Environmental Microbiology, the scientists concluded: "It is possible that this finding represents the persistence of the livestock-associated strain of CC398 in hospital settings in the United Kingdom, with onward transmission between humans. Such a scenario should be investigated with more intensive sampling."