Exam #5: Bacterial Infections of the GI Tract I Flashcards
What elements of the GI tract in the host can trigger expression of bacterial virulence factors?
1) Mucus
2) Bile
Where is the highest density of normal flora in the GI tract?
Large intestine
What are the functions of the GI microbiota? What are the good functions? What are the bad functions?
Good=
- Competitive exclusion
- Production of vitamins
Bad=
- Digestion of undigested or indigestible compound, which can be bad b/c bacteria sometimes digest things into carcinogens
Also, note that there is currently research investigating the link between normal microbiota & hunger/obesity
Define gastritis.
Inflammation of the stomach
Define gastroenteritis.
Inflammation of the stomach and intestines
Define diarrhea.
Frequent loose & fluid filled stool (typically from disease in the small intestine)
Define dysentery.
Inflammatory disorder of the GI tract often associated with:
- Diarrhea with blood & pus in the feces
- Pain, fever, & abdominal cramps
- Usually results from disease of the large intestine
Define Enteritis.
Inflammation of the intestines, especially the small intestine
Define Enterocolitis.
Inflammation of the mucosa of the small and large intestine
Define Colitis.
Inflammation of the large intestine
What is the presentation of inflammatory bacterial infection of the GI tract?
Some bacterial pathogens cause intestinal inflammation, which is damaging to the intestine & results in:
- Fecal occult or visible blood
- Fecal leukocytes
What are the bacteria that are associated with inflammatory bacterial GI infection?
Salmonella Campylobacter jejuni C. difficle EHEC EIEC Shigella Vibrio parahaemolyticus Yersinia enterocolitica
What is the presentation of non-inflammatory bacterial GI infection?
Other bacteria pass through the intestine or are adherent to the intestinal epithelium and:
1) Don’t produce toxins
2) Produce a toxin that does NOT damage the cell (but may cause a change in electrolyte or H20 efflux)
What bacteria are associated with non-inflammatory bacterial GI infection?
EPEC
ETEC
Vibrio cholerae
Listeria moncytogenes
What organisms cause bloody diarrhea?
Campylobacter jejuni C. difficle EHEC EIEC Shigella Vibrio parahaemolyticus Yersinia enterocolitica
What organisms cause watery diarrhea?
EPEC
ETEC
Vibrio cholerae
Listeria moncytogenes
What are the generalized symptoms of bacterial GI tract infections?
Diarrhea
Vomiting
Fever
Abdominal discomfort
The onset of symptoms after ingestion of bacteria is significant. What can be determined about the bacteria from this kind of information?
Onset 1-8 hours after ingestion=
- Preformed toxins
Onset 8-16 hours after ingestion=
- Production of toxin after ingestion
Onset 16+ hours after ingestion=
- Adherence, growth & virulence factor production
What bacteria are associated with symptom onset 1-8 hours after ingestion?
Staphylococcus aureus
Bacillus cereus (emetic)
Clostridium botulinum
What bacteria are associated with symptom onset 8-16 hours after ingestion?
Bacillus cereus (diarrheal)
Clostridium perfringens
Clostridium botulinum
What bacteria are associated with symptom onset 16+ hours after ingestion?
Shigella Salmonella Listeria monocytogenes E. Coli Campylobacter Vibrio
What are the two types of bacterial food poisoning? What are the symptoms?
1) Toxins produced by bacteria in food before the food is consumed
2) Large numbers of spores are ingested, spores germinate in intestine & vegetative bacteria produce toxins without any colonization or adherence to the GI tract
Symptoms:
- Diarrhea
- Vomiting (both)
NO FEVER
What are the four most common bacterial causes associated with food poisoning?
Staphylococcus aureus
Clostridium botulinum
Clostridium perfringes
Bacillus cereus
List the characteristics of Staphylococcus aureus. What are the symptoms of food poisoning with S. aureus?
Gram (-) cocci in clusters
Catalase positive
Coagulase positive
Ingestion of a preformed toxin causes severe vomiting, diarrhea, & abdominal pain between 1 & 8 hours after consumption .
*Toxin is heat-stable & MOA is not understood. Treatment is supportive therapy.
List the characteristics of Colstridium botulinum.
Gram (+) rod
Anaerobic growth test positive
Spore forming
What causes the symptoms of C. botulinum infection? What is the mechanism of action?
Botulinum toxin:
- Early: vomiting, diarrhea, & abdominal pain 1-8 hours post ingestion (if ingestion of preformed toxin, 6-18 hours after ingestion if large number of spores)
- Late: flaccid paralysis, progressive muscle weakness, & respiratory arrest
Botulism toxin works at the NMJ to prevent release of pre-synaptic ACh
What is Clostridium botulinum infection associated with?
- Home-canning (improperly)
- Infants & honey
Parents are instructed not to let their children eat honey prior to 1 year because of this.
Remember that BOTulinum is from bad BOTtles of food & honey
What are the complications of Clostridium botulinum infection?
- Lingering weakness
- Dyspnea (up to 1 year after primary disease)
What is the treatment for Clostridium botulinum?
- Supportive therapy
- IV anti-toxin administration
What is infant botulism? How does this compare to adult disease?
- “Floppy baby syndrome”
- Less severe
Caused by germination of C. botulinism spores in the intestines, which is often ingested when infants are fed honey. Affects infants because of permeability of intestinal mucosa (which changes ~6 months; thus, parents are told to wait till 1 year for honey ingestion–playing it safe).
Remember that while adult disease is caused by preformed toxin, infant disease is caused by spores.
What are the characteristics of Clostridium perfringens?
Gram (+) rod
Anaerobic growth test positive
Spore-forming
What is Clostridium perfringens associated with?
Contaminated meat products & gravies that are held below recommended temperatures
What are the symptoms of Clostridium perfringens food poisoning? What causes these effects?
C. perfringens enterotoxin leads to:
- Diarrhea & abdominal cramps 8-16 hours post- ingestion
- Symptoms last ~24 hours
What are the characteristics of Bacillus cereus?
Gram (+) rod
Anaerobic growth test negative
Spore forming
Motile
What is Bacillus cereus food poisoning associated with?
Improper storage of cooked rice (emetic) & meat/ vegetables (diarrheal)
How do Bacillus cereus emetic & diarrheal forms differ? Specifically, what is the implicated food, cause, onset of symptoms, symptoms, & enterotoxin?
Emetic=
- Rice
- Preformed toxin
- 15 min- 8 hours
- Vomiting, nausea, abdominal cramps
- Heat stable enterotoxin
Diarrheal=
- Meat & vegtables
- Toxin produce in intestine
- 8-16 hours
- Diarrhea, nausea, abdominal cramps
- Heat liable
What are the characteristics of Helicobacter pylori?
Gram (-) “curved” rod
Microaerophilic
What diseases are associated with Helicobacter pylori?
Ulcers
Chronic gastritis
*Considered to be a type I carcinogen
Describe the Helicobacter pylori mechanism of action.
1) Penetrates the mucous of the intestinal epithelium, attached by chemotactic substances, hemin & urea
2) H. pylori recruits & activates inflammatory cells. Simultaneously, H. pylori releases urease that cleaves urea, producing NH3 that neutralizes stomach acid in the vicinity
3) Cytotoxin & ammonia produced by urea cause destruction of mucous producing cells, exposing the underlying connective tissue to erosive stomach acid
How is Helicobacter pylori infection diagnosed?
- Urea breath test
- Biopsy
What is the treatment for Helicobacter pylori infection?
*Only treat after a positive test for Helicobacter pylori
Combination of:
- antibiotics
- Proton pump inhibitor (controls acid & prevents further mucosal damage)
Describe the characteristics of Listeria monocytogenes.
Gram (+) rod
Anaerobic test negative
Non-spore forming
Motile
What are the key survival traits of Listeria monocytogenes?
- Wide temperature growth range
- Resistant to high salt concentrations
- Wide pH range
What is Listeria monocytogenes infection associated with?
Animal reservoirs
- Mammals, birds, & fish
Contaminated food
- Ready to each meat
- Raw vegetables
Who is at high risk for Listeria monocytogenes infection?
Young
Elderly
Immunocompromised & especially pregnant women
Note that human to human transmission is possible, primarily from the mother to fetus
What are the clinical manifestations of Listeria monocytogenes in healthy adults?
Usually asymptomatic, but may have:
- Fever
- nausea
- diarrhea
What are the clinical manifestations of Listeria monocytogenes in immunocompromised adults?
Bacteremia (bacteria in blood)
- fever
- malaise
- chills
- Without obvious focus
Meningitis & encephalitis (indistinct from other causes of meningitis)
*Note that ANY pregnant woman presenting with fever, malaise, & chills without no obvious focus should have a blood culture because of the risk of transferring the disease to the neonate
What are the clinical manifestations of Listeria monocytogenes in neonates?
- Granulomatosis infantiseptica
- Meningitis & encephalitis
Note that transmission in utero can result in: premature birth, abortion, or still birth
What is granulomatosis infantiseptica?
Pyogenic granulomas distributed over the whole body
Describe the mechanism of action of Listeria monocytogenes.
1) Adherence and induced uptake mediated by Internalin-A
2) Internalized into an endocytic vacuole
3) Acidificationn of vacuole/ phagosome activates Listeriolysin O, which disrupts the vacuole & allows escape into the cytosol
4) Replication in the cytosol
5) ActA mediated actin polymerization leading to spread to neighboring cells & bloodstream
6) Disseminated infection
How is Listeria monocytogenes infections diagnosed?
Microscopy=
- Insensitive
Culture
- Cold enrichment selection
- Beta-hemolysis
- Motility test
How is Listeria monocytogenes treated?
Beta-lactam, or
Trimethoprim-sulfamethoxazole
Note that there is no vaccine variable–this is why you should properly cook animal meats & was raw vegetables
What bacterial organism is associated with infection of the stomach?
Helicobacter pylori
What bacterial organism is associated with infection of the small intestine?
Listeria monocytogenes
