lecture 17: microbial diseases of the digestive system edith porter, m.d. 1
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Lecture 17: Microbial diseases of the digestive systemEdith Porter, M.D.
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Structure & function and normal microbiota of the digestive system
Bacterial diseases Mouth: dental caries, periodontal disease Lower digestive system: peptic ulcer disease, food poisoning,
cholera, gastroenteritis, salmonellosis, typhoid fever, C. difficile antibiotic associated diarrhea
Viral diseases Mumps, gastroenteritis, hepatitis
Fungal diseases Ergot and aflatoxin poisoning
Protozoan diseases Giardiasis, cryptosporidiosis, amoebiasis
Helminthic diseases Tapeworm, pinworm, hookworm, ascariasis, trichinellosis
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>700 species in mouth Viridans
strepotcocci Many anaerobes Spirochaetae No only bacteria
Few in the stomach due to low pH
Few in small intestine due to special defense cells
Large numbers in large intestine, including: Lactobacillus Enterococcus E. coli Enterobacter Klebsiella Proteus Bacteroides
Microbes contribute to ~ 40% of the weight of feces
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Transmitted via food and waterFecal-oral cycle can be broken by:
Proper sewage disposal Disinfection of drinking water Proper food preparation and storage
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Oral bacteria convert sugars to acid
Acid damages tooth enamel
Most cariogenic is S. mutans Biofilm and
subsequently plaque formation
Chewing sugar free gum reduces caries
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Teeth affected, begins on the teeth
Gums affected in-between the teeth Inflammation and degeneration of
structures that support teeth
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Chronic Peptic ulcer caused by H. pylori
Intoxication (food poisoning) caused by ingestion of toxin Symptoms appear 1-48 h after ingestion Treated with fluid and electrolyte replacement
Infection caused by pathogen multiplying in the intestine and producing various toxins Incubation from 12 h to 2 weeks Symptoms usually include diarrhea,
gastroenteritis, dysentery Treated with fluid and electrolyte replacement
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Causes peptic ulcer disease Produces urease (urea
carbon dioxide + ammonia, increases pH), a cytotoxin, and continuously attracts and activates neutrophils
Urease detection used in rapid assays
Treated with antibiotics Chronic H. pylori infection
may lead to stomach cancer
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Staphylococcus aureus enterotoxin is a superantigen
In intestine, it acts as neurotoxin
Nausea, vomiting
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Food poisoningUndercooked rice Ingestion of bacterial exotoxin
produces mild symptoms
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Caused by Vibrio cholerae serotypes that produce cholera toxin Infection rate higher in individuals with impaired gastric acid
production Toxin causes host cells (enterocytes) to secrete electrolytes and
water 12 – 20 L, rice water stool
Toxin does not destroy the enterocyte, no inflammation and no fever
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Most important genera E. coli Salmonella Shigella Yersinia
Identified biochemically and by serotyping with antisera specific for certain surface structures
Symptoms depend on toxin produced Enterotoxin: cholera like, watery diarrhea (E. coli) Cytotoxin (shiga toxin) bloody diarrhea with
inflammation, fever (E. coli, Shigella) Endotoxin mediated: general inflammation, fever
Dysentery: diarrhea with leukocytes in stool as sign of a severe inflammation, accompanied by fever and possibly blood 15
Refer to surface structures H-antigen is part of flagella O-antigen located on LPS K or Vi- (Samonella) antigen - capsule
High antigenic variability16
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Certain strains produce shiga like toxin
Toxin is resorbed and enters circulation
Bacteria remain in the intestine on top of the cells, not inside
Toxin is transported to small vessel
Microvascular endothelial cell damage Inhibition of protein synthesis Apoptosis Platelet activation
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DiseasedNormal
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Ingested Requires large dose
(105) Sources include
chicken and reptiles like turtles
Salmonella enterica serovars such as S. enterica Typhimurium
Affects small intestine Mortality (<1%) due to
septic shock caused by endotoxin
Systemic in immunocompromised
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Salmonella enterica Typhi Human adapted Low infectious dose (~1000) Enter through small intestine Bacteria routinely spread throughout
body in phagocytes High fever, continued headaches Diarrhea only during 2.. and 3. week
when fever declines 1-3% recovered patients become
chronic carriers, harboring Salmonella in their gallbladder 23
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Human to human
Animal product to human
Two component signal transduction Sensor and response
regulator Type III secretion
apparatus Injects proteins directly
into host cell “Hypodermic needle” Injected proteins cause
host toengulf bacterium, prevent fusion of salmonella vacuole with lysosomes, cause diarrhea 25
Induced uptake and intracellular survival in macrophages and enterocytes
Shigella spp. producing Shiga toxin (cytotoxin)
Affects colon Shiga toxin causes
inflammation and bleeding, diarrhea
Dysentery with leukocytes in stool
Typically no systemic spread
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Y. enterocolitica and Y. pseudotuberculosis
Can reproduce at 4°CUsually transmitted in meat and
milkAssociated with arthritis
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Campylobacter jejuniMicroaerophilic gram negative
rods (not member of enterobacteriacea)
Usually transmitted in cow's milkLinked to Guillian-Barre syndrome,
an autoimmune neurological disorder with temporary paralysis
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C. difficile is part of normal microbiota in large intestine
Proliferates and secretes toxins when patient takes antibiotics
Toxins destroy epithelial cells, induce diarrhea , and attract neutrophils Pseudomembranous enterocolitis
Recently, transmission in hospitals noted
MumpsGastroenteritisHepatitis
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Mumps virus Enters through respiratory
tract Infects parotid glands and
leads to painful swelling and fever
May cause orchitis (infection of the testis that may lead to infertility), even less frequently meningitis, inflammation of ovaries, and pancreatitis
Prevented with MMR vaccine 32
Rotavirus 3 million cases annually 1-2 day incubation, 1
week illness Norovirus
50% of U.S. adults have antibodies
1-2 day incubation. 1-3 day illness
Treated with rehydration
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Inflammation of the liverHepatitis may result from drug or
chemical toxicity, EB virus, CMV, or the Hepatitis viruses
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Giardia Flagellated Duodenal infection, prolonged symptoms, may
interfere with food absorption Duodenal fluid is used for diagnosis
Cryptosporidium Numerous stools, cholera like, weight loss Often in AIDS patients Acid fast cysts in stool are diagnostic
Entamoeba Uptake of cysts with are activated by stomach acid Severe dysentery with bloody diarrhea (E.
histolytica) Amoeba (not cysts) with ingested erythrocytes in
stool is diagnostic37
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MycotoxinsProduced by some fungi
Claviceps purpurea▪ Grows on grains▪ Produces ergot (LSD like)▪ Toxin restricts blood flow to limbs; causes hallucination
Aspergillus flavus▪ Grows on grains▪ Produces aflatoxin▪ Toxin causes liver damage; liver cancer
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Caries is a result from biofilm and plaque formation and acid production due to S. mutans and other bacteria
Differentiate food poisoning with ingestion of preformed toxin from gastroenteritis due to pathogens proliferating in the intestine that may produce enterotoxins (watery diarrhea) or cytotoxins (bloody diarrhea with dystentery)
Food poisoning: enterotoxins from S. aureus, B. cereus Gastroenteritis due to bacterial obligate pathogens
(Salmonella, Shigella, Yersinia, Campylobacter, Cholera); bacterial opportunistic pathogens (some E. coli strains); viruses (Rota virus and Noro virus); protozoa (Giradia, Cryptosporidium, Entamoeba histolytica); helminths
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1) Which of the following statements about salmonellosis is false?A) It is a bacterial infection.B) It requires a large infective dose.C) A healthy carrier state exists.D) The mortality rate is high.E) It is often associated with poultry products.
2) Which of the following feeds on red blood cells?A) Giardia lambliaB) Escherichia coliC) Taenia spp.D) Vibrio parahaemolyticusE) Entamoeba histolytica
3) Most of the normal microbiota of the digestive system are found in theA) Mouth.B) Stomach.C) Small intestine.D) Large intestine.E) C and D.
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