Biliary microbiome and gallstones: A silent friendship

Abstract

With increasing evidence, the biliary tract and the gallbladder mucosa are no longer considered sterile environments devoid of bacteria. Rather a profound biofilm of resident bacterial flora is associated with the mucosal surface. The bile too harbors a resident flora. It is when a dysbiotic process ensues, that this bacterial flora either becomes opportunist or is replaced by a pathogenic one that has a strong ability to survive the challenges of the biliary environment. Although once believed a metabolic problem, recent evidence indicates a complex interaction between different species of bacteria and gallbladder mucosa and bile which may culminate in calculus formation. The resident microbiota and its several enzymes dictate the type of gallstone by the mere interplay of the constituting type of bacteria in the biofilm, even without any evidence of infection. Dysbiosis is often mediated by either intestinal dysbiosis or less probably by oral dysbiosis. The gallstones, in turn, provide a haven for the resident microbiota in which they can form their own defined niche enriched with the biofilm that can resist the biliary defense mechanisms and survive the hostile biliary environment in the background of biliary stasis and local infection. However, this process of silent friendship is more complex than said, and further research is needed to define the relationship between the two.

Keywords: Biliary microbiome; Resident flora; Dysbiosis; Gallstones; Β-glucuronidase

Core Tip: The concept of the existence of a resident biliary microbiome has been emerging in recent times. There is a well-established association between this microbiome and gallstone formations. Dysbiosis in the biliary microbiome rather than infection is the key phenomenon responsible for gallstone formation as evident from the emerging metagenomics-based studies.