Salmonella variants found in pigs pose different threats to human and animal health, a DNA study found.
Two closely related variants of Salmonella Typhimurium – a major cause of gastroenteritis worldwide – have significantly different effects on pig health, a study has found.
The two variants, termed U288 and ST34, are particularly dominant in pigs and differed in colonisation of the intestine and surrounding tissues and the severity of disease they produced, scientists from the Roslin and the Quadram Institutes found.
A unique set of genetic changes was found in the U288 variant, which probably occurred between 1980 and 2000, that may hold the key to understanding how this variant interacts differently with pigs during infections and in the food chain, the researchers suggest.
Findings from the study could help to predict the risk of Salmonella variants to animals and people, and aid the design of strategies to prevent or control infections.
The study analysed the genetic makeup of Salmonella strains isolated from pigs and people over many years, to identify variants and understand how they evolved and behave.
The ST34 variant accounts for more than half of all S. Typhimurium infections in people, while the U288 variant is rarely associated with human infection.
Samples were collected from human clinical infections during routine diagnosis and from animals during routine surveillance. The U288 variant evolved to acquire genes associated with antimicrobial resistance and variations in molecules linked to virulence. This variant grew more slowly in the lab and was more sensitive to stress associated with dehydration, scientists observed.
The study, published in the journal Communications Biology, involved collaboration with the Earlham Institute, Public Health England and the Animal and Plant Health Agency. It was funded by the Biotechnology and Biological Sciences Research Council, part of UK Research and Innovation.
Understanding how variants of Salmonella emerge and pinpointing the genetic signatures responsible for adaptation to different hosts and the ability to produce disease will provide opportunities to improve diagnostics and surveillance. In turn this will help to predict the risk that Salmonella variants pose to animal health and food safety.
We have seen these types of changes before in variants of Salmonella that have become adapted to specific host species and cause a more invasive disease, including the type of Salmonella that causes typhoid fever in people but does not affect other species.