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 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

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

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

Normal and Diseased Gums

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

Ulcer formation by H. pylori

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

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

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

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

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

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

Mechanism of Shigella

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)

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

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

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

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

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

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

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.

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

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

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

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