Gallstones
Research has shown that Salmonella species form biofilms on the surfaces of gallstones, where the bacteria in them are protected from high concentrations of bile and antibiotics.
Salmonella enterica serovar Typhi, which causes typhoid fever in humans, crosses the gut and invades macrophages. The macrophages carry the organism to the liver, pancreas and spleen, where the bacteria are thought to replicate. From the liver, they are shed into the gallbladder, where they either cause an active infection (cholecystitis) or a chronic infection (carrier state). The carrier state occurs in 3 – 5% of infected people and is frequently associated with gallbladder abnormalities, such as gallstones. This infection is often asymptomatic and can last for many years with little or no serious effect on the infected person. Furthermore, it has been shown that the chronic carrier state is the single most important risk factor for development of hepatobiliary carcinomas, as evidenced by the finding that Salmonella carriers with gallstones have an 8-fold-greater risk for developing cancer of the gallbladder.
Individuals with gallstones are more likely to become typhoid carriers, and antibiotic treatments are less effective against Salmonella enterica serovar Typhi in carriers with gallstones.
It is interesting that Salmonella are found in the gallbladder, considering that it is also the storage site for bile. Bile is produced in the liver and consists of many components, including bile salts, cholesterol and bilirubin. Bile salts are like detergents that aid degradation and dispersion of fats, making bile a good antimicrobial agent. Salmonella, however, is resistant to high concentrations of bile and bile salts.
Antibiotic treatment can be ineffective in Salmonella carriers with gallstones, and elimination of gallbladder infection in these individuals usually requires gallstone removal. However, this option is less likely in several developing countries where S. enterica serovar Typhi is prevalent.
Further reading on biofilms and gallstones
Prouty, A. M., Schwesinger, W. H., & Gunn, J. S. (2002). Biofilm formation and interaction with the surfaces of gallstones by Salmonella spp. Infection and immunity, 70(5), 2640–2649. https://doi.org/10.1128/IAI.70.5.2640-2649.2002.
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