FRIDAY, SEPTEMBER 30, 2016

Researchers track animal-borne drug-resistant bacteria with genome sequencing

Researchers used whole genome sequencing to determine if drug-resistant bacteria moved from animals to humans in two Denmark disease outbreaks, according to a study published on Monday in EMBO Molecular Medicine.

The researchers determined the outbreaks were caused by animal-to-human transmission of methicillin-resistant Staphylococcus aureus that carries the mecC gene. The gene gives the bacteria resistance to the antibiotic methicillin. Drug-resistant bacterial infections can cause severe and fatal consequences.

Costs of whole genome sequences are dropping and the speed of analysis has increased. As a result, scientists are more able to use whole genome sequencing to conduct disease-related investigations.

"We used whole genome sequencing to see if we could determine if the two disease outbreaks were caused by the same bacterium and to investigate if the pathogens were transmitted from animal to humans or the other way around," Mark Holmes, the senior author of the paper, said. "At first glance, it seems reasonable to expect the same pathogen to be the source of the two outbreaks at the two geographically close locations. By looking at the single differences in nucleotides or SNPs in the DNA sequences of each isolate, it became obvious that two different strains of bacteria were responsible for the two disease outbreaks. In one case, the results also clearly showed that the most likely direction of transmission was from animal to human."

The researchers used an Illumina HiSeq sequencing system to examine the nucleotide sequence of each pathogen. They compared single differences in nucleotides in the two sequences and determined the identity of the pathogens and their routes of infection.

"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," Ewan Harrison, a lead author on the study, said.

The researchers said that whole genome sequencing cannot replace other more traditional methods of disease analysis, though it can give scientists an increased ability to distinguish between different pathogens as causes of disease.

MRSA can cause debilitating soft tissue and skin infections, pneumonia and bacteremia.