Transcript Digestive System Infections

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Esophagus and stomach are
relatively bacteria free
Mouth
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Small Intestine—few microbes
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Different Streptococci in
different micro environments
Teeth colonized by bacteria
forming biofilm—plaque 1012
bacteria per gram!
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
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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
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Symptoms
› Diarrhea
 Dysentery: blood and pus in feces
› Loss of appetite
› Nausea and vomiting
› fever
Fecal-oral transmission (contaminated
water supply)
 Dehydration as result of diarrhea
 Generalities in pathogenic mechanisms:
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> 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
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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
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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
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› 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
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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
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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
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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
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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
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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
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Symptoms
› Fatigue, fever, abdominal pain, jaundice
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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
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Prevention by vaccination and avoidance
Most common blood-borne infection in the
US
 Symptoms similar to Hepatitis A or B or
asymptomatic.
 Viroid
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› Enveloped ss-RNA flavivirus
No vaccine
 Pathogenesis
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› 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
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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
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Symptoms are generally
mild but can be chronic
› Amebic dysentery