TAILIEUCHUNG - Chapter 122. Acute Infectious Diarrheal Diseases and Bacterial Food Poisoning (Part 2)

Pathogenic Mechanisms Enteric pathogens have developed a variety of tactics to overcome host defenses. Understanding the virulence factors employed by these organisms is important in the diagnosis and treatment of clinical disease. Inoculum Size The number of microorganisms that must be ingested to cause disease varies considerably from species to species. For Shigella, enterohemorrhagic Escherichia coli, Giardia lamblia, or Entamoeba, as few as 10–100 bacteria or cysts can produce infection, while 105–108Vibrio cholerae organisms must be ingested orally to cause disease. The infective dose of Salmonella varies widely, depending on the species, host, and food vehicle. . | Chapter 122. Acute Infectious Diarrheal Diseases and Bacterial Food Poisoning Part 2 Pathogenic Mechanisms Enteric pathogens have developed a variety of tactics to overcome host defenses. Understanding the virulence factors employed by these organisms is important in the diagnosis and treatment of clinical disease. Inoculum Size The number of microorganisms that must be ingested to cause disease varies considerably from species to species. For Shigella enterohemorrhagic Escherichia coli Giardia lamblia or Entamoeba as few as 10-100 bacteria or cysts can produce infection while 105-108 Vibrio cholerae organisms must be ingested orally to cause disease. The infective dose of Salmonella varies widely depending on the species host and food vehicle. The ability of organisms to overcome host defenses has important implications for transmission Shigella enterohemorrhagic E. coli Entamoeba and Giardia can spread by person-to- person contact whereas under some circumstances Salmonella may have to grow in food for several hours before reaching an effective infectious dose. Adherence Many organisms must adhere to the gastrointestinal mucosa as an initial step in the pathogenic process thus organisms that can compete with the normal bowel flora and colonize the mucosa have an important advantage in causing disease. Specific cell-surface proteins involved in attachment of bacteria to intestinal cells are important virulence determinants. V. cholerae for example adheres to the brush border of small-intestinal enterocytes via specific surface adhesins including the toxin-coregulated pilus and other accessory colonization factors. Enterotoxigenic E. coli which causes watery diarrhea produces an adherence protein called colonization factor antigen that is necessary for colonization of the upper small intestine by the organism prior to the production of enterotoxin. Enteropathogenic E. coli an agent of diarrhea in young children and enterohemorrhagic E. coli which causes hemorrhagic

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