Cambridge scientists have linked two human cases of infection with the antibiotic- resistant superbug MRSA to farms in Denmark. The results of the study, published today in the journal EMBO Molecular Medicine, suggest the methicillin-resistant Staphylococcus aureus (MRSA) bacteria was transmitted from the livestock to the farmers.

The type of MRSA which was found in both of the human cases was only discovered two years ago by Dr Mark Holmes and his colleagues from the University of Cambridge. The new strain’s genetic makeup differs greatly from previous strains, which means that the ‘gold standard’ molecular tests currently used to identify MRSA - a polymerase chain reaction technique (PCR) and slide agglutination testing - do not detect it.

For this study, the scientists used whole genome sequencing to investigate two cases of the new MRSA where the patients lived on farms to see if the same strain could be found in the animals on the farm.

Dr Holmes, from Cambridge’s Department of Veterinary Medicine and the senior author on the paper, said: “Having found this new MRSA in both people and animals on the same farm it was likely that it is being transmitted between animals and people.

“By looking at the single differences in nucleotides, or SNPs, in the DNA sequences of each isolate, it became obvious that in both farms we looked at the human and animal MRSA were almost identical. In one case, the results also clearly showed that the most likely direction of transmission was from animal to human.”

The study raises questions about whether cows could be a reservoir for new strains of MRSA. It was previously not clear whether MRSA was transmitted to cows from humans or to humans from cows, but the new research indicates that the livestock is the likely source of these new strains.

“Our findings demonstrate that the MRSA strains we studied are capable of transmission between animals and humans, which highlights the role of livestock as a potential reservoir of antibiotic resistant bacteria,” remarked Dr Ewan Harrison, a post-doctoral research associate at the University of Cambridge’s Department of Veterinary Medicine and co-author of the paper.

For more information about this story, please contact: Genevieve Maul, Office of Communications, University of Cambridge. Email: Genevieve.Maul@admin.cam.ac.uk; Tel: 01223 765542.