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Digestive Diseases – Microbiology Lecture Online

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Microbiology STLCC

Diseases of Body Systems *Digestive

Diseases of Digestive Tract 

I. Bacterial Diseases of GI Tract

A. Dental Caries (Cavities)

1. Bacteria accumulate on teeth surface and hydrolyze sucrose to glucose and fructose

2. Glucose is used to produce “sticky” dextran

3. Dental plaque is bacteria (400 species, 100’s of cells thick) and dextran

4. Fructose is converted lactic acid

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5. Acid erodes enamel; leads to cavity

6. Streptococcus mutans – most cariogenic

a. Hide in crevices, tolerant of acid, synthesize dextran


B. Gingivitis

1. Infection of gums (gingivae)

2. Periodontitis

a. Infection spreads to bone and tissue supporting teeth


II. Lower GI Tract

A. Gastroenteritis

1. Inflammation of stomach and intestinal mucosa

B. Infection of GI Tract

1. Microbes enter and multiply; penetrate mucosa

2. Delay in symptoms as microbes multiply

C. Intoxication of GI Tract

1. Ingestion of bacteria toxin

2. Sudden onset of symptoms

D. Infection and Intoxication

1. Cause cramps, nausea, vomiting, diarrhea

2. Vomiting and diarrhea is mechanism to get rid of problem

3. Dysentery – severe diarrhea with blood/mucus


E. Staphylococcal Food Poisoning

1. Leading cause of gastroenteritis

2. Intoxication from enterotoxin produced by S. Aureus

3. Toxin is heat stable, i.e. once it is produced reheating will not destroy it

4. Toxin triggers vomiting, cramping and diarrhea

5. They do not spoil food; hard to detect

6. Proper refrigeration will prevent toxin formation

Events of Typical Food Poisoning

1. Food is cooked (any bacteria killed)

2. Food is then contaminated by worker with S. aureus on hands

3. Food left at room temperature; S. aureus incubate in food and produce toxins

4. Food is reheated, may kill S. aureus but not toxins

5. Food is served and eaten

6. Staphylococcal intoxication (food poisoning) occurs in 1-6 hours


F. Shigellosis (Bacillary Dysentery)

1. Infection – onset of symptoms is longer (12 hours or more); fever

2. Caused by Shigella genus

3. Mild species cause traveler’s diarrhea

a. Traveler’s diarrhea also caused by E. coli, salmonella, campylobacter

4. Virulent species cause severe dysentery, dehydration, significant mortality rate

a. Shiga toxin – after infection Shiga toxin is produced (damaging to intestines)


G. Salmonellosis (Salmonella gastroenteritis)

1. Infection by Salmonella bacteria

2. Onset of symptoms 12-36 hours (nausea, abdominal pain, diarrhea)

3. Sources include poultry, eggs

4. Generally do not treat with antibiotic; just oral rehydration

H. Cholera

1. Causative agent is Vibrio cholera

2. Grow in small intestine and produce an exotoxin (cholera toxin)

3. Exotoxin causes host cells to secrete water and electrolytes (K+)

a. Watery stools with mucus and epithelial cells

4. Major water and electrolyte loss ———-à shock and death

a. If untreated, 50% mortality rate

I. Escherichia coli (E. coli) Gastroenteritis

1. Most are not pathogenic

2. E. coli 0157:H7

a. E. coli food poisoning

b. Shiga-toxin-producing E. coli

c. Cattle (although not affected) are the reservoir

d. Contamination occurs at slaughter

e. Leafy vegetables can also become contaminated

f. Can cause hemorrhagic colitis, hemolytic uremic syndrome (kidney failure)


J. Campylobacter gastroenteritis

1. Campylobacter jejuni is leading cause of food-borne illness in US

2. Commonly found in chicken

3. Abdominal cramps, diarrhea, dysentery, fever


K. Helicobacter pylori

1. Causative agent of most stomach ulcers

2. Can live in acid of stomach because they produce urease which hydrolyzes urea to

ammonia. NH3 is alkaline.


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