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Chapter 10 : The Interaction of Bile Salts with Pathogenic and Nonpathogenic Intestinal Bacteria
Category: Food Microbiology; Applied and Industrial Microbiology
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This chapter provides an overview of bile composition and conjugation mediated by the normal flora and its aforementioned antimicrobial effects. It discusses known molecular mechanisms behind bile resistance and the role bile has in altering the virulence of enteric pathogens. Fasting and malnourishment have been shown to decrease the amount of bile in the intestine and, consequently, leave individuals vulnerable to bacterial pathogens. Similar to commensal enteric bacteria, pathogenic Listeria monocytogenes contains bile salt hydrolases (BSH) genes thought to confer bile resistance and successful colonization and disease manifestation. Probiotics researchers suggest that subsequent limitations to enterohepatic circulation in the presence of unconjugated bile acids cause enhanced fecal loss of bile salts. The chapter talks about the effect of bile on pathogenic bacteria. Adaptability to the harsh effects of bile acids is a critical component of survival for gastrointestinal pathogens. Both conjugated and unconjugated bile salts increased expression of the CmeABC efflux pump, while other antimicrobials, including chloramphenicol, ethidium bromide, and erythromycin, did not affect transcription of cmeABC. Surface plasmon resonance provided evidence that bile salts were capable of inhibiting binding of CmeR to the cmeABC promoter, leading to increased pump expression and elevated bile resistance. Interestingly, the presence of bile salts in culture media enhanced the resistance of Campylobacter to multiple antibiotics, including cefotaxime, novobiocin, and fusidic acid. As long as the integrity of the normal microbial flora is maintained, compounds that are mentioned in the chapter could be manufactured to target known factors contributing to bile resistance.
Bacterial intestinal pathogens discussed in this chapter that are affected by bile. Listed are microbes known to cause acute or chronic disease in the gallbladder or the intestinal tract. Interactions between invading microorganisms and bile, which is produced in the liver and found in the intestine and gallbladder, affect various genes and virulence properties (listed) that enhance colonization and persistence.