Week 5: Gastrointestinal Infections

Hello everyone, this week we discussed gastrointestinal tract infections.  One of the key points made during this lecture was the mechanisms of pathogenicity of the various bacteria that cause GI infections.  I have decided to make a chart of the different modes of pathogenicity to as study aid for everyone for our upcoming test.  Hope you all find it helpful!

Mechanism of Pathogenicity	Description	Symptoms	Bacterial agents
Toxin production – enterotoxin	No invasion, toxin acts on adenylate cyclase enzyme to catalyze conversion of ATP to cAMP, cells secrete more ions into the lumen of the intestine which is followed by water, causes watery diarrhea	Non-bloody, watery stools, vomiting, abdominal cramps, stool negative for RBCs and PMNs	Enterotoxigenic E. coli, Vibrio cholerae, Vibrio parahemolyticus (other vibrios), Clostridium perfringens, Clostridium difficile (toxin A), Bacillus cereus, others
Toxin production – cytotoxins	Cytotoxins act to disrupt the structure of the intestinal epithelial cells, causing cells to slough off from the mucosa causing inflammation	Dysentery – blood and PMNs in the stool, accompanied by pain, cramps and tenesmus	Enterohemorrhagic E. coli, C. difficile, (toxin B), others
Toxin production – neurotoxins	Usually preformed in food and ingested, emetic toxin causes vomiting indpedent of of other actions on the mucosa, and the neurotoxin produced by Clostridium botulinum prevents the release of acetocholine at nerve junctions, resulting in flaccid paralysis	Vomiting, paralysis	S. aureus, Bacillus cereus, Clostridium botulinum
Invasion	Invasion of GI mucosal cells by bacteria, resulting in inflammation and dysentery	Blood and PMNs in stool	Shigella, Salmonella, Enteroinvasive E. coli, Campylobacter jejuni
Invasion of full bowel wall with lymphatic spread	Diarrhea not often presenting symptom		Salmonella typhi - bacteremia (typhoid fever); Yersinia enterocolitica - mesenteric lymphadenitis
Attachment	Adhere to, destroy, and interfere with normal function of cells of the bowel	Malabsorption problems, diarrhea	Enteropathogenic E. coli, Giardia lamblia