The Sphincter of Oddi is a Boundary for Bacterial Colonisation in the Feline Biliary Tract

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Abstract
The autochthonous microbial flora of the gastrointestinal and biliary system were studied in ten cats using standard bacteriological cultures and electron microscopic techniques. The most common organisms isolated from the gastrointestinal tract were streptococci, anaerobes and coliform bacteria. A spiral organism was identified in the feline stomach and duodenum. The bile and the biliary system were entirely sterile except in one cat. Bacteria were isolated from the sphincter of Oddi. Electron microscopy confirmed that bacteria had colonised in the thick mucous layer in the gastrointestinal tract and the sphincter of Oddi. No bacteria could be found above the sphincter by electron microscopy. The sphincter of Oddi is hence the natural boundary and probably serves as a physical barrier to the upward migration of bacteria from the colonised gastrointestinal tract to the uncolonised biliary system. The cat may be a suitable animal model for bacteriological studies of the biliary system in the human.