BIOL 251 Chapter 24

Digestive tract immune defense mechanisms

• Low pH of the stomach

• Peristalsis

• Mucous production

• Normal microbiota

• Peyer’s patches (with M cells)

Gastritis

Stomach inflammation

Enteritis

Intestinal mucosa inflammation

Gastroenteritis

Inflammation of both stomach and intestines

Hepatitis

Liver inflammation

Colitis

Colon inflammation

Dysentery

Severe colon damage causing bloody, mucous-filled stool

Food Poisoning (Staphylococcus aureus)

• Cause: Ingestion of heat-stable exotoxins from contaminated food

• Symptoms: Rapid onset vomiting, diarrhea (within hours); resolves in 24 hrs

• Foods: Often undercooked or kept below 60°C

• Pathogenesis: Toxin survives stomach acid and damages GI cells

Lower digestive tract infection

• Symptoms: Diarrhea, nausea, vomiting, sometimes fever

• Transmission: Fecal-oral; contaminated food, water

• Mechanisms: Invasion, toxin production (enterotoxins cause fluid loss; cytotoxins kill cells)

Salmonellosis Characteristics

• Agent: Salmonella enterica (e.g., Enteritidis, Typhi)

• Symptoms: Diarrhea, nausea, vomiting, fever (lasts days–weeks)

• Pathology: Invasion of small intestine, inflammation causes diarrhea

• Transmission: Undercooked poultry, eggs, reptiles

Salmonella

• Susceptible Groups: Children, immunocompromised

• Virulence Factors: Adhesion to epithelial cells, capsule (Typhi), intracellular survival

• Prevention: Proper cooking, hygiene; typhoid vaccine

• Treatment: Often self-limiting; antibiotics in severe cases

E. Coli Characteristics

• Gram-negative rod, some strains pathogenic

• Symptoms: Ranges from watery to bloody diarrhea, cramps

• Pathology: Adhesion (fimbriae), enterotoxins

• Transmission: Contaminated food, water; unpasteurized drinks

E. Coli

• Susceptible: Infants, travelers

• Pathogenic Groups:

  • ETEC – Traveler’s diarrhea

  • EHEC/STEC – Bloody diarrhea, HUS

  • EPEC – Pediatric diarrhea

  • EIEC – Invasive, dysentery-like illness

• Virulence: Toxins (e.g., Shiga), adhesion molecules

• Prevention: Hygiene, pasteurization

• Treatment: Rehydration; avoid antibiotics in EHEC (can worsen HUS)

Shigella characteristics

• Non-motile Gram-negative rods; four species

• Symptoms: Dysentery, fever, cramps, vomiting, possibly HUS

• Pathology: Invades M cells, escapes macrophages, invades epithelial cells

• Virulence: Shiga toxin (S. dysenteriae), cell invasion

• Transmission: Fecal-oral; low infectious dose

Shigella

• Susceptible: Infants, developing countries

• Treatment: Rehydration; antibiotics (some resistance); no vaccine

Helicobacter pylori

• Spiral Gram-negative, motile, microaerophile

• Survival: Produces urease to neutralize stomach acid

• Disease: Gastritis, peptic ulcers, possibly cancer

• Pathogenesis: Invades mucosa, reduces mucus protection

• Treatment: Antibiotic combo therapy

Clostridium difficle characteristics

• Gram-positive anaerobe, spore-forming

• Symptoms: Diarrhea, colitis, pseudomembranous colitis, toxic megacolon

• Transmission: Fecal-oral; spores resist disinfectants

Clostridium difficile

• Susceptible: Elderly, hospitalized, recent antibiotics

• Virulence: TcdA (enterotoxin), TcdB (cytotoxin)

• Treatment: Stop antibiotics if possible, rehydration, vancomycin or metronidazole, fecal transplants in severe cases

• Prevention: Hand hygiene, careful antibiotic use

Vibrio Cholerae characteristics

• Curved, Gram-negative rod; salt and alkaline tolerant

• Symptoms: Severe watery diarrhea, up to 20L/day, vomiting, cramps

• Transmission: Contaminated water, seafood, vegetables

Vibrio Cholerae

• Virulence: Cholera toxin (A-B toxin increases Cl⁻ secretion)

• Treatment: Rapid rehydration, antibiotics if needed

• Prevention: Clean water, sanitation, oral vaccine for travelers

Hepatic Viruses

• infect hepatocytes

• A: Fecal-oral; acute; vaccine available

• B: Blood/body fluids; chronic; cancer risk; vaccine available

• C: Bloodborne; often chronic; no vaccine

• D: Requires HBV co-infection

• E: Fecal-oral; rare in U.S.

Rotavirus

Severe in children; fecal-oral; vaccine available

Norovirus

Very contagious; common in enclosed spaces; self-limiting