Microbial Diseases of the Digestive System

Chapter 25

Defenses of digestive system

• Stomach: acidic

• Small intestine: phagocytic cells that produce lysozyme, rapid movement of food prevents bacteria from colonizing small intestine

• 70% of the immune system is located in the intestinal tract
  – Gut-associated lymphoid tissue (GALT)

  • Lymph nodes

  • Peyer’s patches

Normal Microbiota of the Digestive System

• Millions of bacteria per milliliter of saliva

• Few microorganisms in the stomach
  – Due to HCl production

• Small intestine
  – Granule-filled phagocytic cells

• Large numbers of bacteria in the large intestine
  – Mostly anaerobes and facultative anaerobes
  – 100 billion bacteria per gram of feces
  – Assist with enzymatic breakdown of some polysaccharides
  – Produce some vitamins

Defenses of digestive system

• Stomach: acidic

• Small intestine: phagocytic cells that produce lysozyme, rapid movement of food prevents bacteria from colonizing small intestine

• 70% of the immune system is located in the intestinal tract
  – Gut-associated lymphoid tissue (GALT)

  • Lymph nodes

  • Peyer’s patches

Normal Microbiota of the Digestive System

• Millions of bacteria per milliliter of saliva

• Few microorganisms in the stomach
  – Due to HCl production

• Small intestine
  – Granule-filled phagocytic cells

• Large numbers of bacteria in the large intestine
  – Mostly anaerobes and facultative anaerobes
  – 100 billion bacteria per gram of feces
  – Assist with enzymatic breakdown of some polysaccharides
  – Produce some vitamins

Gingivitis

Gingivitis is inflammation of the gums
• Caused by poor oral hygiene
• Steps of infection:
• Plaque formation. This is a sticky film of bacteria and dextran

Gingivitis and tooth decay

Streptococcus mutans digests sucrose and makes dextran. Bacteria and dextran make up dental plaque

Streptococcus mutans produces lactic acid that
breaks down enamel leading to tooth decay that
can advance to tissues of the jaw

Steps of tooth infection

1. Plaque formation. This is a sticky film of bacteria and dextran

2. Plaque turns to tartar which is hard to remove and forms a protective layer around bacteria

3. If not removed, the tartar irritates the gum around the tooth and causes inflammation. Gums become swollen and bleed easily

4. Infection can get into underlying tissues and bone, and result in bone loss.

Diseases of Lower Digestive System

• Infection: growth of a pathogen
  –Incubation is from 12 hours to 2 weeks
  –Fever

• Intoxication: ingestion of toxin
  –Symptoms appear 1 to 48 hours after ingestion

• Gastroenteritis: inflammation of stomach and intestinal mucosa leading to diarrhea, dysentery

Salmonellosis

• Caused by Salmonella species

• Bacteria invade intestinal mucosa and multiply

• Source of infection is intestines of animals (chicken, eggs)

• Several cases in Wisconsin due to contaminated peaches, red onions, veggie trays, etc....

Salmonellosis

Virulence factors of Salmonella

Salmonella

• Imost people, Salmonella infections may not cause symptoms

• Some develop fever, diarrhea, and abdominal cramps

• Complications include bacteremia (bacteria in the blood).

  • This can lead to infection of the brain, spinal cord, heart, and blood vessels

• Prevention:

  • Washing hands

  • Avoid eating raw eggs

  • Store raw meat, poultry and seafood away from other foods in your refrigerator

  • Never place cooked food on an unwashed plate that previously held raw meat

Staphylococcal Food Poisoning

Caused by Staph. aureus, an inhabitant of nasal passages

Most common form of gastroenteritis

Intoxication due to heat stable toxin

The sequence of events in a typical outbreak of staphylococcal food poisoning

Cholera

• Caused by Vibrio cholerae

  • Vibrio cholerae serotypes that produce cholera toxin

  • Toxin causes host cells to secrete Cl−, HCO−, and water

Vibrio cholera

Source: contaminated water, uncooked seafood, human fecal contamination

Infection results in watery diarrhea (or rice water diarrhea), and can result in dehydration and death

Cholera toxin causes secretion of chloride ions by intestinal epithelial cells; this alters ionic balance and results in diarrhea

Cholera toxin acquired by lysogenic conversion

Peptic Ulcer disease

• Sores that develop on the lining of the stomach or small intestine

• Symptoms include:
  • Burning stomach pain
  • Heartburn
  • Nausea

• Spicy food or stress do not cause ulcers, but they make symptoms worse

• Infection caused by the bacterium Helicobacter pylori

Peptic Ulcer disease

• H. pylori is a common inhabitant of the mucus that lines the intestinal tract.

• Under normal conditions, bacterium does not cause disease

• Roughly 50% of the world’s population have this bacterium in their body

• 2005 Nobel Prize was given to to Robin Warren and Barry Marshall for their discovery of Helicobacter pylori and its role in gastritis and peptic ulcer disease

Helicobacter pylori infection

Cryptosporidiosis

Cryptosporidiosis