BIOL 251 chapter 24 study points

Immune defense mechanisms of Digestive System

• Low ph of stomach

• Peristalsis

• Mucus production

• Normal microbiota

• Peyers 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 blood, mucus-filled stool

Staphylococcus aureus food poisoning

• Ingestion of heat-stable exotoxins from contaminated food

• Rapid onset vomiting, diarrhea (resolves in 24 hrs)

• Cause: often undercooked foods or kept below 60 degrees C

• Toxin survives stomach acid and damages GI cells

Lower Digestive Tract Infection

• Diarrhea, nausea, vomiting, sometimes fever

• Fecal-oral, contaminated food, water

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

Salmonellosis

Symptoms: Diarrhea, nausea, vomiting fever (lasts day-weeks)

• invasion of small intestine, inflammation causes diarrhea

Cause: undercooked poultry, eggs, reptiles

• Children and immunocompromised people are more susceptible

Treatment: often resolves on its own; antibiotics for severe cases

Causative agent: Salmonella enterica (S. Typhi)

Virulence factors of Salmonella

• Adhesion to epithelial cells

• Capsule (Typhi)

• Intracellular survival

Prevention of Salmonella

• Proper cooking

• Hygiene

• Typhoid vaccine

E. Coli characteristics

• Gram-negative rod

• Some pathogenic strains

E. Coli

Symptoms: Ranges from watery to blood diarrhea, cramps

Pathology: Adhesion (fimbriae), enterotoxins

Transmission: contaminated food and water; unpasteurized drinks

Susceptible: Infants, travelers

Prevention: Hygiene, pasteurization

Pathogenic groups of E. Coli

• ETEC – Traveler’s diarrhea

• EHEC/STEC – Bloody diarrhea, HUS

• EPEC – Pediatric diarrhea

• EIEC – Invasive, dysentery-like illness

E. Coli virulence factors

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

• 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

• Susceptible: Infants, developing countries

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

Helicobacter pylori

• Characteristics: 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 difficile

• Characteristics: Gram-positive anaerobe, spore-forming

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

• Transmission: Fecal-oral; spores resist disinfectants

• 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 cholera

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

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

• Transmission: Contaminated water, seafood, vegetables

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

• Treatment: Rapid rehydration, antibiotics if needed

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

What cells are does hepatitis 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