Animal link to salmonella in humans may be “overstated”

Animals may not be the cause of a drug-resistant type of salmonella, despite previous beliefs.

According to a new study, genetic profiles examined in both animals and humans are very different, and the contribution from animals to drug-resistant salmonella infections in humans “may previously have been overstated”.

It also found the bacteria in the samples, taken mainly from Scotland, remained within their original host populations and that there were more varied combinations of drug resistance in the human-infecting bacteria.

A total of 373 salmonella samples were studied by the Wellcome Trust Sanger Institute over 22 years and “researchers found that distinguishable bacterial populations exist in human and animal populations living side by side”, according to the institute.

Head of industry development with Quality Meat Scotland (QMS) Andy McGowan said: “The results of this study confirm our long-held view that - while it is very important that antibiotics are administered to animals responsibly - agriculture has been disproportionately blamed as the source of drug-resistant salmonella. This report makes it clear there are other potential sources of resistance which need to be explored in parallel.”

The researchers are currently speculating that international travel and imported foods could be the major sources of the drug-resistant strains, but more research will be needed for this to be confirmed.

First author of the study Dr Alison Mather said: “For the first time we’ve determined in detail and on a large scale how salmonella strains taken from humans and animals in the same setting and over the same time period relate to each other. Our genomic data reveal how the salmonella bacteria spread during the course of a long-term epidemic. We found that people have a more diverse source of infection and antibiotic resistance than just the local animals, pointing towards alternative sources.”

The new research is vital as antibiotic resistance in humans is considered as one of the most important dangers to human health.

Senior author from the Wellcome Trust Sanger Institute Professor Nicholas Thomson said: “This is a study that uses the latest genomic approaches and a unique collection of samples to address a significant public health problem. Our data provide a very simple message, challenging the established view that local animals are the predominant source of salmonella infections in Scotland. This finding will reinvigorate discussions on the sources of antibiotic-resistant salmonella infections in humans in other environments.”