25. Microbial Diseases of the Digestive System

Question 1

1. What are the characteristics of tooth decay?

Answer 1

• Dental caries (tooth decay)
  
  • Dental Plaque - Biofilm formation on teeth
  • Streptococcus mutans is the most important cariogenic organism
    
    • Gram-positive coccus
    • Converts sucrose to lactic acid
    • Produces dextran, a polysaccharide that forms plaque
  • Plaques attract other carcinogenic bacteria
  • Caries penetrate from enamel into the dentin
    
    • Caused by gram-positive rods and filamentous bacteria
  • Decay can reach pulp, which contains the blood supply and nerve cells
    
    • May advance to the soft tissues, leading to abscesses

Question 2

2. What are the differences between gingivitis and periodontitis?

Answer 2

• Gingivitis
  
  • Inflammation and infection of the gums characterized by bleeding
  • Caused by streptococci, actinomycetes, and anaerobic gram-negative bacteria
• Periodontitis
  
  • Bone and tissue supporting the teeth are destroyed
  • Caused by Porphyromonas

Question 3

3. What causes staphylococcal food poisoning?

Answer 3

• Staphylococcal food poisoning
  
  • Pathogen – Staphylococcus aureus
  • Intoxication – from an enterotoxin (superantigen)

Question 4

4. What is the key difference in symptoms for Shigellosis compared to Salmonellosis

Answer 4

• Shigellosis (bacillary dysentery)
  
  • Pathogen – Shigella spp.
  • Symptoms – tissue damage and dysentery
  • Damage to the intestinal wall and can invade the blood stream
  • Infection Produces endotoxin and Shiga exotoxin
• Salmonellosis
  
  • Pathogen is Salmonella enterica – gram-negative, facultative anaerobe, nonendospore-forming rods
  • Invades intestinal mucosa and multiplies
  • Symptoms are fever, pain, nausea, cramp and diarrhea
  • Infection endotoxin

Question 5

5. What infections can Salmonella cause?

Answer 5

• Salmonella causes endotoxin infection – Typhoid fever, Food poisoning, gastroenteritis, enteric fever

Question 6

6. What is the causative agent of cholera?

Answer 6

• Vibrio cholerae
• Grows in the small intestine and produces an exotoxin, cholera toxin, that causes host cell to secrete water and electrolytes, especially potassium

Question 7

7. What diseases are caused by E. coli?

Answer 7

• Escherichia coli gastroenteritis
  
  • Pathogenic E. coli
  • Attach to intestinal cells with fimbriae
  • Produce toxins
  • May aggregate
• Shiga toxin-producing E. coli (STEC)
  
  • Shigella-like dysentery, hemorrhagic colitis and hemolytic uremic syndrome (blood in urine that often leads to kidney failure)
  • Infection and shiga-like exotoxin
  • Treated with quinolones or cephalosporins
• Traveler’s diarrhea
  
  • Watery diarrhea treated by oral rehydration
  • Infection and endotoxin

Question 8

8. What is the reservoir for Campylobacter gastroenteritis?

Answer 8

• chicken and cow’s milk/feces
• retail red meats seem to be less likely
• a gram-negative, microaerophilic, spirally curved

Question 9

9. What is the causative agent of peptic ulcer disease?

Answer 9

• Helicobacter pylori
• Grows in the stomach acid by producing urease, converts urea to alkaline ammonia, disrupts stomach mucosa, causing inflammation

Question 10

10.What is the reservoir for Yersinia gastroenteritis?

Answer 10

• they inhabit intestines of domesticated animals
• often transmitted by eating raw or undercooked pork
• they can grow in refrigerated blood, especially transfusing blood

Question 11

11.Why is mumps considered a viral disease of the digestive system?

Answer 11

• Mumps virus targets the parotid glands
  
  • The parotid glands secrete water, salts, and starch-digesting amylase during digestion
• respiratory tract - lymph nodes - viremia - then the parotid glands final stop

Question 12

12.What are types of fungal diseases of the digestive system?

Answer 12

• Mycotoxins: toxins produced by fungi
  
  • Ergot poisoning
    
    • Mycotoxins produced by Claviceps purpurea
    • Occurs in grains
    • Restricts blood flow to limbs (gangrene) and causes hallucinations
  • Aflatoxin poisoning
    
    • Mycotoxins produced by Aspergillus flavus
    • Likely to be found on food and peanuts
    • Causes liver cirrhosis and liver cancer

Question 13

13.What are types of protozoan diseases of the digestive system?

Answer 13

• Giardiasis
  
  • Caused by Giardia lamblia
  • Flagellated protozoan adheres to intestinal wall
  • Form cysts in feces and water
  • Leads to prolonged diarrhea, malaise, weight loss, flatulence and cramp
  • Water or mammal reservoir
• Cryptosporidiosis
  
  • Caused by Cryptosporidium parvum and Ceryptosporidium hominis
  • Invade the intestinal epithelium
  • Cholera-like diarrhea
  • Cattle and water reservoir
• Cyclospora diarrheal infection
  
  • Caused by Cyclospora cayetanesis
  • Human and bird reservoir and causes watery diarrhea
• Amoebic dysentery (amoebiasis)
  
  • Caused by Entamoeba histolytica
  • Produces cysts that survive stomach acid
  • Feces contain blood and mucus
  • Human reservoir that leads to abscesses with a high mortality rate

Question 14

14.What are types of helminthic diseases of the digestive system?

Answer 14

• Tapeworms
  
  • Beef tapeworm: Taenia saginata
  • Pork tapeworm: Taenia solium
  • Fish tapeworm: Diphyllobothrium latum
  • Ophthalmic cysticercosis: larvae lodge in the eye
  • Neurocysticercosis: larvae develop in the central nervous system
• Hydatid Disease
  
  • Caused by the tapeworm Echinococcus granulosus
  • Eggs are ingested and migrate to the liver, lungs, or brain
  • Develops a hydatid cyst
  • Can grow and hold up to 15 liters of fluid
  • May rupture, causing tissue damage and anaphylactic shock
• Nematodes
  
  • Pinworms caused by Enterobius vermicularis
    
    • Leads to itching around the anus
    • Detected by microscopy
    • Autoinoculation is common
    • Eggs are sticky, so easily transmitted
  • Hookworms
    
    • Caused by the nematodes Necator americanus and Ancylostoma duodenale
    • Attaches to the intestinal wall and feeds on blood and tissue
    • Anemia, lethargic behavior, and craving for peculiar foods (pica)
    • Carried from human feces in soil that contact bare skin
  • Ascariasis
    
    • Minimal symptoms, but worms will emerge from various locations including the naval, anus, mouth or nose
    • Caused by the nematode Ascaris lumbricoides
    • 30% of the worldwide population is infected
    • Eggs shed in the feces and are ingested by another person
  • Whipworm (Trichuris trichoura)
    
    • Can survive for years feeding on cell contents and blood without detection if numbers are low
    • Causes anemia, malnutrition and retarded growth
  • Trichinellosis
    
    • Occurs from ingestion of undercooked pork
    • Caused by Trichinella spiralis
    • Fever, eye swelling, gastrointestinal upset