GI infections Flashcards
Predisposing factors for GI infections (5)
- Travel to area with poor hygiene- direct exposure to sewerage
- Fecal contaminated food or water
- Food products not properly cleaned or cooked
- Previous, prolonged antimicrobial treatment
- Immunosuppressed patients suffer disseminated infections
Anatomy of the GI tract
Alimentary canal- includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, anus
Functions of the GI tract (2)
- Absorption of nutrients
- Excretion of waste products
GI host defense mechanisms (6)
- Peristalsis
- pH
- Mucus, lysozyme, proteases, lipases
- Secretory IgA
- Phagocytes
- Normal flora
Upper GI tract infections
Impact the stomach and duodenum. Infections include gastritis and peptic ulcerative disease
Lower GI tract infections
Impacts the small and large intestines. Symptoms- diarrhea, dysentery (purulent, mucous, bloody), cramping and abdominal pain
Normal flora of the upper small intestine (2)
- Streptococci
- Lactobacilli
10 - 1000 organisms/mL
Normal flora of the distal ileum (2)
- Enterobacterales
- Bacteroides sp.
106 - 107 organisms/mL
Normal flora of the large bowel (5)
Newborn: human epithelial flora, mostly gram-positive. Adult: mostly anaerobic (1000:1), approximately 1010-11 bugs/mL
1. Bacteroides sp.
2. Clostridium sp.
3. Peptostreptococcus sp.
4. Bifidobacterium sp.
5. Eubacterium sp., etc.
aerobe: Escherichia coli & other Enterobacterales, enterococci & other streptococci
Nosocomial pathogens (5)
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Antimicrobial-resistant gram-negative rods
- Clostridioides difficile
- Candida albicans
Pathogenic mechanisms of enteric pathogens (3)
- Adherence to intestinal mucosa
- Toxigenic
- Invasion of the mucosal epithelium
Adherence to intestinal mucosa
Pathogens would have this mechanism prevent normal absorption and normal secretory function
Toxigenic infection mechanism
Intoxication- organisms growing in the GI tract produce toxins. Enterotoxins act primarily in the small intestine and produce a profuse and watery stool. WBCs and RBCs are not a prominent feature
Pathogenic invasion of mucosal epithelium
Cell destruction. There is occasional invasion of the bloodstream and systemic disease
Gram positive pathogens (5)
- S. aureus
- Bacillus cereus
- Clostridium perfringens Type A
- Clostridium botulinum
- Clostridioides difficile
S. aureus
Gram positive. Produces an enterotoxin. Severe nausea and vomiting begin 2 to 8 h after ingestion, typically followed by abdominal cramps and diarrhea, often lasting < 12 h.
Bacillus cereus
Gram positive. Produces an emetic toxin and an enterotoxin. The emetic toxin is heat and pH stable. Onset of symptoms takes 1-6 hours, and they last for less than 24 hours. There is nausea and vomiting but no fever, and diarrhea is rarely found. The toxin is pre-formed and is on food- found on contaminated rice, noodles, pasta, and cakes. The enterotoxin requires ingestion of 10^6 organisms/gram. Onset of symptoms takes 8-24 hours, and they last approximately 24 hours. Symptoms include abdominal pain and diarrheal disease. Found in cream sauces, cooked meat, poultry, vegetables, and desserts
Clostridium perfringens Type A
Gram positive. This is a common cause of food poisoning and causes mild, self limited disease. The bacteria produces a toxin after the organism is ingested. Symptom onset is 8-12 hours after ingestion. Includes large numbers of neutrophils, positive for occult blood. symptoms: pain, cramps, tenesmus. The organism is found in meats and gravies
Clostridium botulinum
Gram positive. Produces a neurotoxin that may cause death by respiratory paralysis. Adults experience intoxication, the microorganism is infrequently recovered from the stool. Infant botulism is not intoxication- the organism is ingested and multiplies, producing toxin
Clostridioides difficile
Gram positive. Antibiotic-associated pseudomembranous colitis, as the organism is usually suppressed by normal flora. There are hospital acquired and community acquired infections. Toxin mediated infection- toxin A is a tissue damaging enterotoxin, toxin B can be detected by CPE in cell culture
Gram negative pathogens
- Salmonella
- Shigella
- Yersinia species
- Escherichia coli
Salmonella species (3)
- Salmonella Typhi - serotype D1, typhoid (enteric fever)
- Salmonella Enteritidis - serotype group D
- Salmonella Typhimurium - serogroup B
Order Enterobacterales, more than 2400 serovars
Shigella species (4)
- S. dysenteriae, group A
- S. flexneri, group B
- S. boydii, group C
- S.sonnei, group D
Order Enterobacterales
Yersinia species (2)
- Y. enterocolitica
- Y. pseudotuberculosis
Motile at 22-30C, NON-MOTILE at 37C.