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Digestive System Infections

Digestive System Infections. Chapter 25. Normal Microbiota. Esophagus and stomach are relatively bacteria free Mouth Different Streptococci in different micro environments Teeth colonized by bacteria forming biofilm —plaque 10 12 bacteria per gram! Small Intestine—few microbes

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Digestive System Infections

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  1. Digestive System Infections Chapter 25

  2. 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

  3. 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

  4. 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

  5. Normal and Diseased Gums

  6. 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

  7. Ulcer formation by H. pylori

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. Mechanism of Shigella

  15. 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)

  16. 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

  17. 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

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

  19. Viral Diseases of Lower Digestive System: Norovirus • Viroid • Small non-enveloped, ss-RNA • Survive well in enviroment • Incubation 12-48 hurs • Considered a type B bioterrorism agent • Not cultivated in laboratory

  20. 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

  21. 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

  22. 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.

  23. 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

  24. 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

  25. 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

  26. 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

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