A new research suggests that typhoid fever bacteria collect on gallstones to perpetuate the disease.
People who harbour these bacteria in their gallbladders, even without symptoms, can infect others with active typhoid fever, especially in developing areas of the world where sanitation is poor. The disease spreads through fecal-oral contact, such as through poor hand-washing by people who prepare food.
Scientists and physicians have long known that these bacteria, Salmonella enterica serovar Typhi, accumulate in the gallbladder. In fact, the most widely accepted treatment of chronic typhoid infection is removal of the gallbladder.
John Gunn, professor of molecular virology, immunology and medical genetics at Ohio State University and senior author of the study, said: "We're trying to get to the heart of why this is. Why does Salmonella sit in a pool of highly concentrated detergent, which is what bile is, but not die?
"It's got to survive in some way, and a good way to survive is by forming a biofilm."
Biofilms, the collection of bacteria on gallstones, typically do not respond well to antibiotics or the human immune response. But now that the biofilms themselves have been discovered in association with asymptomatic typhoid infection, they present a potential treatment alternative to expensive and invasive gallbladder removal, said Gunn, who is also a vice director of Ohio State's Center for Microbial Interface Biology.
In particular, targeting a sugar polymer on the bacterial surface that promotes development of the biofilm might be a strategy to prevent biofilm formation in the first place, he said.
Gunn and his team analysed this biofilm formation in mice infected with a strain of Salmonella bacteria similar to the strain that causes typhoid fever in humans. The scientists also detected these biofilms on gallstones in about 5 percent of humans in a Mexican hospital who had their gallbladders removed because of complications from gallstones.
Gunn said: "The mouse data coupled with the human data suggest strongly that biofilms lay a foundation that allows for establishment and maintenance of chronic typhoid infection."
The research has been published in the online early edition of the Proceedings of the National Academy of Sciences.