1. Digestive System Infections
Chapter 25

3. Normal Microbiota Esophagus and stomach are relatively bacteria free
Mouth
Different Streptococci in different micro environments
Teeth colonized by bacteria forming biofilm—plaque 1012 bacteria per gram!
Small Intestine—few microbes
Aerobic and facultative anaerobes
Gram-negative rods, streptococci, lactobacillus, yeast
Large Intestine (1/3 fecal mass):
Bacteroides--anaerobic
Enterobacteria—facultative anaerobes

4. Normal Microbiota of the Digestive System
Actions
Synthesis of Vitamins:
Niacin, thiamine, riboflavin, pyridoxine, folic acid, pantothenic acid, biotin, and vitamin K
Digestion of fiber—gas production!
Opportunistic pathogens of urogenital tract
Prevent colonization by pathogens
Antibiotic treatament that disrupts normal flora can result in diarrhea
Antibiotic-associated colitis due to colonization by clostridium difficile

5. Bacterial Diseases of Upper Digestive Tract--Mouth
Tooth decay
Dental caries
Streptococcus mutans
Produce lactic acid and thrive in acid environment
Produce extracellular glucans, base for biofilm
Prevention: decrease refined sugar, mechanical removal of plaque, fluoride
Periodontal disease
Caused by plaque formation and tartar in gingival crevice
Gingivitis
“Trench mouth” Acute necrotizing ulcerative gingivitis: poor dental hygiene and stress
Treponema sp., anaerobic spirochete

6. Normal and Diseased Gums

7. Gastritis Helicobacter pylori
Generally asymptomatic unless accompanied by ulcers or cancer
Survive in stomach acid due to urease which converts urea to ammonia
Flagella allow penetrataion of mucosal layer and attachment to mucosal epithelium

8. Ulcer formation by H. pylori

9. Viral Diseases of Upper Digestive System: Herpes Simplex
Cold Sores and Fever Blisters
HSV-1
Ds-DNA
Enveloped virus
Latent infection of sensory nerve endings
Life-long infection,
treatment of symptoms does not remove latent virus
Transmitted in saliva either directly or by fomits (2-3 hours)
Large portions of the population are infected with the virus

10. Viral Diseases of Upper Digestive System: Mumps
Acute viral infection of parotid gland
Paramyxovirus
Ss-RNA virus
Infects parotid, pancreas, ovary, testicles
Immune response produces symtomatic swelling and accompanying pain
Complications can include: meningitis, orchitis, miscarriage, encehpalitis.
Vaccination aims at eradication of mumps

11. Diseases of Lower Digestive System: Gastroenteritis, or “Stomach flu”
Causitive agents
Microbial toxins (food intoxication)
Bacterial infection
Viral infection
Protozoa infection
Symptoms
Diarrhea
Dysentery: blood and pus in feces
Loss of appetite
Nausea and vomiting
fever

12. Bacterial Diseases of the Lower Digestive System
Fecal-oral transmission (contaminated water supply)
Dehydration as result of diarrhea
Generalities in pathogenic mechanisms:
Attachment: pili or adhesin (proteins)
Toxin production
Increase secretions
cytotoxin
Alteration of host cells
Type III secretion
Cell invasion

13. Bacterial Diseases of the Lower Digestive System: Cholera
Vibrio cholerae
Curved, gram-negative rod
Salt tolerant
Acid sensitive
Produce exotoxin: cholera toxin
A-B toxin stimulates adenyl cyclase and locking cAMP cycle in “on” position
Stimulates Cl- secretion resulting in loss of water and electrolytes from the cells
Treatment focuses on oral rehydration therapy
Prevention: avoidance and vaccination

14. Bacterial Diseases of the Lower Digestive System: Shigellosis
Causitive agent:
S. flexneri, S. boydii, S. sonneri, and S. dysenteriae
Gram-negative enterobacteria with plasmid
Acid tolerent
Increasingly antibiotic resistent
Invasion of intestinal epithelial cells
Dysentery
Shiga toxin
A-B cytoxin: inhibits ribosome
Hemolytic uremic syndrome (HUS)
RBC lysis, anemia, kidney failure

15. Mechanism of Shigella

16. Bacterial Diseases of the Lower Digestive System: E. coli
Normal flora
Pathogenic forms identified as cause of
Epidemic gastroenteritis, 1945
traveler’s diarrhea, 1970s
Dysentery and HUC
Pathogenicity:
Enterotoxigenic (plasmid mediated)
Enteroinvasive
Enteroaggregative (plasmid mediated)
Enterohemorrhagic (Shiga toxin production)

17. Bacterial Diseases of the Lower Digestive System: Salmonellosis
Salmonella enterica and S. bongori
Gram-negative, lactose-negative, Acid sensitive
Over 2400 serotypes indicated with non-italicized name
Zoonotic
Source of increased antibiotic resistance
Human reservoir—typhoid fever
Enteric fever: S. typhii
Gastroenterisis
Adhesion and Type III secretion

18. Bacterial Diseases of the Lower Digestive System: Campylobacteriosis
C. jejuni isolated in 1972: leading cause of diarrhea in US
Mobile, gram-negative rod
Microaerophile
Pathogenisis
Invasion of intestinal epithelium causing inflammatory response
Guillain-Barre syndrome complication in 0.1% of cases
Progressive paralysis
5% fatality, 95% recovery with treatment

19. Viral Diseases of Lower Digestive System: Rotavirus
Viroid
Double walled capsid
Ds, segmented RNA
Gastroenteritis
Abrupt onset vomiting and diarrhea
Fluid replacement therapy

20. Viral Diseases of Lower Digestive System: Norovirus
Viroid
Small non-enveloped, ss-RNA
Survive well in enviroment
Incubation hurs
Considered a type B bioterrorism agent
Not cultivated in laboratory

21. Viral Diseases of Lower Digestive System: Hepatitis A
Infectious Hepatitis
HAV
Small ss-RNA picornavirus
Liver is only infected organ
Spread through fecal contamintion of food and water
Symptoms
Fatigue, fever, abdominal pain, jaundice
Vaccine available since 1995

22. Viral Diseases of Lower Digestive System: Hepatitis B
Serum hepatitis
Infects 5% of world population and 9th leading cause of death
HBV virus—hepadanvirus
Ds-DNA, Lipid envelope, reverse transcriptase
HBsAg: surface antigen responsible for adhesion and infection
Long term infections result in cirrhosis of the liver and liver cancer
Spread in blood, blood products, semen, and vertically to newborns
Prevention by vaccination and avoidance

23. Viral Diseases of Lower Digestive System: Hepatitis C
Most common blood-borne infection in the US
Symptoms similar to Hepatitis A or B or asymptomatic.
Viroid
Enveloped ss-RNA flavivirus
No vaccine
Pathogenesis
Inflammation of liver
Chronic infection leading to 10-20% cirrhosis or liver cancer.

24. Protozoan Diseases of the Lower Digestive System: Giardiasis
Giardia lamblia
6-20 day incubation
1-4 week symptoms
Traveller’s diarrhea and local outbreaks
Present in water systems and spring water
Cysts are resistant to water purification chemicals, removed by filtration

25. Protozoan Diseases of the Lower Digestive System: Cryptosporidiosis
Cryptodporidium parvum
Gastroenteritis symptoms
Parasite of the intestinal epithelium
More resistant to chemical treatment and filtration than Giardia
Infects both human and animal populations
Person to person spread is possible

26. Protozoan Diseases of the Lower Digestive System: Cyclosporiasis
Cyclospora cyetanensis
Spore forming protozoan
Gastroenteritis symptoms begin at about 1 week and last 3-4 days, relapse common up to 4 weeks.
No person to person spread, no animal sources identified

27. Protozoan Diseases of the Lower Digestive System: Amebiasis
Entamoeba histolytica
Sarcodina species with cyst form that survives stomach acid
Some strains produce cytotoxin that allows entry into deeper tissue or blood
Symptoms are generally mild but can be chronic
Amebic dysentery