Digestive System Infections
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Transcript of Digestive System Infections
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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Viroid› Double walled capsid› Ds, segmented RNA
Gastroenteritis› Abrupt onset vomiting and
diarrhea› Fluid replacement therapy
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Viroid› Small non-enveloped, ss-
RNA› Survive well in enviroment› Incubation 12-48 hurs
Considered a type B bioterrorism agent› Not cultivated in
laboratory
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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
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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
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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.
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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
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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
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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
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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