33 - Bacterial Infections of the GI Tract I Flashcards
What is diarrhea?
The passage of 3 or more loose or liquid stools per day
Can diarrhea be deadly?
Yes
It is the second leading cause of death in children under 5 worldwide
Leading cause of malnutrition in children under 5
How many cases of diarrhea do we see each year?
- 7 billion cases
- Bad drinking water
- Poor sanitation
What is a gastrointestinal tract infection?
Infections caused by bacteria, viruses and parasites
How are gastrointestinal tract infections transmitted?
Almost all through the fecal-oral route
What is the exception to the fecal-oral route of transmission?
Feces-contaminated water
Where must a GI infection enter the body?
Through the mouth
What characteristic must an infectious agent have in order to survive in the GI tract?
Able to survive in the low pH of the stomach
This typically takes care of most bacteria, but some are resistant
What are the 8 characteristics of the GI tract that contribute to the host defense?
1 - Continuous epithelium 2 - Mucus 3 - Low pH (stomach) 4 - Gut motility 5 - Shedding of epithelium 6 - Bile 7 - Secretory IgA 8 - Normal microbiota
Which two of the host defenses actually trigger the expression of bacterial virulence factors in some infections?
Mucus and bile
What part of the GI tract has the most diverse natural flora?
Large intestine
The microbiota of the stomach and small intestine is much less dense and diverse than in the large intestine
What does competitive exclusion mean?
This is a feature of our normal microbiota that is beneficial by preventing pathogens from infecting the GI tract.
The “bad bacteria” has to compete with the “good bacteria,” preventing disease.
What does it mean that the normal microbiota can digest “undigestible” compounds?
The normal microbiota are able to digest certain things that we can’t… This can be good or bad.
They can digest certain carcinogens, which may be linked to GI cancer
Are the normal microbiota of the GI tract able to affect the innate and adaptive immune systems?
Yes
What is gastritis?
Inflammation of the stomach
What is gastroenteritis?
Inflammation of the stomach and intestines
What is dysentery?
Inflammatory disorder of the GI tract often associated with:
- Diarrhea with blood and pus in the feces
- Pain, fever, abdominal cramps
- Usually resulting from disease of the large intestine
What is enteritis?
Inflammation of the intestines, especially the small intestine
What is enterocolitis?
Inflammation of the mucosa of the small and large intestine
What is colitis?
Inflammation of the large intestine (colon)
When a bacterial pathogen causes inflammation within the intestinal tract, what does this cause?
Damage to the intestines
What is fecal occult?
Microscopic blood in the feces
You can’t see it in the stool, so you will need to test for it
When there is inflammation in the intestines is it more or less likely that you will see fecal occult?
More likely
When there is inflammation in the intestines, are you more or less likely to see fecal leukocytes?
More likely
What are the common pathogens of the GI tract that cause inflammation?
- Salmonella spp.
- Campylobacter jejuni
- C. difficile (severe cases)
- EHEC
- EIEC
- Shigella spp.
- Ibrio parahaemolyticus
- Yersinia enterocolitica
What are non-inflammatory GI bacteria?
These are bacteria that are passing through the intestines or adhering to the intestinal epithelium, but they either do NOT contain a toxin or they produce a toxin that is NON-cytotoxic
What is a non-cytotoxic toxin?
It is a toxin that is able to increase electrolytes and water efflux in the GI tract, but does NOT kill cells (it affects them in some other way)
What are some examples of non-inflammatory GI bacteria?
- EPEC
- ETEC
- Vibrio cholerae
- Listeria monocytogenes
What types of bacteria produce watery diarrhea that is sometimes or often times bloody?
- EHEC
- Campylobacter jejuni
- Shigella spp.
- Yersinia enterocolitica
- EIEC
- Clostridium. Difficile
- Vibrio parahaemolyticus
What types of bacteria produce watery diarrhea, but is rarely bloody?
- EPEC
- ETEC
- food-poisoning
- Clostridium perfringens
- Bacillus cereus
- Vibrio cholerae
- Salmonella spp.
- Listeria monocytogenes
Can GI pathogens cause disease outside of the GI tract?
Yes, many can
What is one very important factor to consider when diagnosing a GI tract infection?
Timing!
What are the generalized symptoms of bacterial GI tract infections?
- Diarrhea
- Vomiting
- Fever
- Abdominal discomfort
What assumptions can you make to help you with diagnosis if the symptoms begin 1-8 hours after ingestion?
The patient ingested a preformed toxin
This means that when they ate the food, the bacteria were already actively releasing the toxin - this accounts for the symptoms beginning right away
Which bacteria would cause symptoms to begin 1-8 hours after ingestion?
- Staphylococcus aureus
- Bacillus cereus (emetic)
- Clostridium botulinum
What assumptions can you make to help you with diagnosis if the symptoms begin 8-16 hours after ingestion?
The patient ingested a bacteria that had not yet produced its toxin
This means that as the bacteria traveled through the patient’s GI tract, they began to actively release a toxin, so the symptoms took a little while to begin
Which bacteria would cause symptoms to begin 8-16 hours after ingestion?
- Bacillus cereus (diarrheal)
- Clostridium perfringens
- Clostridium botulinum
What assumptions can you make to help you with diagnosis if the symptoms begin more than 16 hours after ingestion?
The bacteria did not release a toxin while they were simply passing though the GI tract, but instead they have adhered to the wall of the intestinal tract and are exhibiting a virulence factor while they are there
Which bacteria would cause symptoms to begin more than 16 hours after ingestion?
- Shigella spp.
- Salmonella spp.
- Listeria monocytogenes
- EHEC
- EPEC
- ETEC
- EIEC
- Campylobacter
- Vibrio spp.
There are two types of bacterial food poisoning. What are they?
1 - Pre-formed toxins
2 - Spores ingested
What type of spores need to be ingested in order to cause bacterial food poisoning?
A large number of spores need to be ingested that germinate in the intestine and become vegetative bacteria
These vegetative bacteria produce toxins, but do not necessarily colonize or adhere to the GI tract, they are just passing through
While they are passing through, they produce toxins
What symptoms will you see from bacterial food poisoning?
- QUICK onset diarrhea, vomiting or both
- NO fever
There are four bacterial causes of food poisoning. What are they?
- Staphylococcus aureus
- Clostridium botulinum
- Clostridium perfringens
- Bacillus cereus
Describe staphylococcus aureus
- Gram-positive cocci in clusters
- Not spore forming
Describe the course of the disease from staphylococcus aureus
- Ingestion of a preformed toxin
- Severe vomiting, diarrhea and abdominal pain
- Onset within 1-8 hours after consumption
What is the pathogenesis of staphylococcus aureus?
- Heat-stable toxin
- Mechanism of action is not well understood
How do you treat staphylococcus aureus food poisoning?
- Supportive therapy
- Hydration
What are the characteristics of colostridium botulinum?
- Gram positive rod
- Spore forming
What causes the symptoms in food poisoning from colostridium botulinum?
The botilism toxin
What are the symptoms in the early onset of the disease?
Early: onset of vomiting, diarrhea, abdominal pain 1-8 h post ingestion of preformed toxin or 8-16 h post ingestion of spores
What are the symptoms in the late onset of the disease?
Flaccid paralysis leading to progressive muscle weakness and respiratory arrest
Can fatality occur from colostridium botulinum?
Yes, from the respiratory arrest
What is the pathogenesis of colostridium botulinum?
Ingestion of…
- Pre-formed toxin
- Large number of spores that germinate in the intestine and produce toxins
What does the major toxin do?
Botulism toxin
- Acts at a neuromuscular nerve junctions and interferes with signaling at synapses
When is food poisoning from colostridium botulinum most commonly seen?
In cases of home-canning
What complications arise?
If the patient survives, you see lingering weakness and dyspnea up to 1 year after the primary disease
How do you treat food poisoning from colostridium botulinum?
- Supportive therapy
- IV anti-toxin drug in severe cases
What does the IV anti-toxin drug do?
Can possibly reverse the progression of the disease in severe cases
Why are parents not advised to give their children honey as infants?
Because spores of colostridium botulinum can be found in honey and can affect infants up to 6-12 months
What is this syndrome called?
Floppy baby syndrome
What happens in floppy baby syndrome?
There is a germination of C. botulinum spores in the intestines which then grow and produce toxins
Is C. botulinum poisoning more severe in infants or adults?
Adults
*Opposite case than normal
What happens around 6 months of age that makes this no longer a concern?
The permeability of the intestinal mucosa changes
What are the characteristics of Clostridium perfringens?
- Gram-positive rod
- Spore forming
What causes the symptoms of the disease?
C. perfringens enterotoxin
What is the disease typically associated with?
Contaminated meat products or gravy that are stored below recommended temperatures
When will you see an onset of symptoms?
- Onset of diarrhea and abdominal cramps 8-16 hours after ingestion
- Lasts approximately 24 hours
What is the treatment for food poisoning by c. perfringens?
Supportive therapy
What are the characteristics of Bacillus cereus?
- Gram-positive
- Spore forming
There are two forms of the disease. What are they?
1 - Emetic form
2 - Diarrheal form
What will you see with the emetic form?
- PRE-FORMED toxin
- Onset of vomiting, nausea and abdominal cramps 1-8 hours after ingestion
Is the pre-formed enterotoxin heat stable or heat sensitive?
Heat stable
What is the emetic form commonly associated with?
Improper storage of cooked rice
Spores can survive the cooking - bacteria can then multiply and produce heat-stable enterotoxin that is inactivated upon reheating
Mechanism of toxin is not known
What will you see with in diarrheal form of bacillus cereus?
- Onset of diarrhea, nausea and abdominal cramps 8-16 hours post-ingestion of contaminated food
- Production of heat-liable enterotoxin in the intestines
What does heat-liable mean?
They will breakdown when exposed to heat
What is a main difference between the emetic form and the diarrheal form of bacillus cereus?
They both produce an enterotoxin
Emetic form = heat stable
Diarrheal form = heat liable
What is the treatment for food poisoning from bacillus cereus?
Supportive therapy
What does helicobacter pylori do once it gets into your system?
It gets into your system and stays there and continues to cause disease
What are the characteristics of helicobacter pylori?
- Gram negative curved rod
- Microaerophilic (5%)
What diseases can be caused by helicobacter pylori?
- Ulcers
- Chronic gastritis
- Stomach cancer in less than 1% of infections
What is the pathogenesis of helicobacter pylori in the stomach?
Not completely understood
- They have flagella
- They secrete the enzyme urease, which catalyzes the conversion of urea to ammonia and carbon dioxide
- They secrete cytotoxin VacA
- They contain adhesins
What is the first step in the formation of a stomach ulcer from helicobacter pylori?
H. pylori penetrates the mucous layer lining of the stomach’s epithelium
It is is attracted to the chemotactic substances, hemin and urea
What is the second step in the formation of a stomach ulcer from h. pylori?
H. pylori recruits and activates inflammatory cells
It also releases urease that cleaves urea, producing NH3 that neutralizes stomach acid in its vicinity
What is the third step in the formation of a stomach ulcer from h. pylori?
H. pylori cytotoxin and the ammonia produced by its urease, cause destruction of the mucus-producing cells, exposing the underlying connective tissue to stomach acid
How do you diagnose a problem with helicobacter pylori in the stomach?
- Urea breath test
- Biopsy
When would you begin treatment for h. pylori?
Only after a positive test for H. pylori
How do you treat h. pylori?
- Antibiotics
- Proton pump inhibitor
What would a proton pump inhibitor do?
Control acid to prevent further mucosal damage
In the small intestine, what characteristics does listeria monocytogenes have?
- Gram positive
- Facultative anaerobic
- Short rods
- Sometimes occurs in pairs
- Inracellular pathogen
What are they key survival traits of listeria monocytogenes?
- Wide growth range (1 degree-45 degrees C)
- Can survive below refrigerator temperature
- Resistant to high salt concentrations
- Wide pH range
How common is listeria monocytogenes?
Fairly rare
- 800 cases per year in the US
Which animals can act as “reservoirs” for listeria monocytogenes?
- Mammals
- Birds
- Fish
What is the PRIMARY source of listeria monocytogenes?
Contaminated food
- Ready to eat meals
- Raw vegetables
What types of patterns do we see with listeria monocytogenes
Both large outbreaks and sporadic cases
Which population is at the highest risk of infection by listeria monocytogenes?
- Young
- Elderly
- Immunocomprimised individuals like pregnant women
Is there human to human transmission?
Yes
Is there mother to baby transmission?
Yes, this is the primary human-to-human transmission type
What is the typical presentation in healthy adults?
- Usually asymptomatic
- May have a fever, nausea and/or diarrhea
What is the typical presentation in immunocompromised?
- Symptoms are NOT distinct
- Fever, persistent headache, stiff neck, vomiting and confusion
What is the rate of mortality in listeria monocytogenes?
20-50%
What are the lasting effects seen in survivors?
Significant neurologic sequelae in survivors
What happens when a pregnant woman becomes infected with listeria monocytogenes?
- May develop nausea, fever and/or diarrhea
- Fever with no obvious infections in blood culture
- Risk of disease transmission to the neonate
What are the symptoms of neonatal infection with listeria monocytogenes?
Granulomatosis infantiseptica
- Pyogenic granulomas that are distibuted over the whole body
- All systems can be involved
- Meningitis
- Encephalitis
What happens in early onset in utero transmission?
- Can result in premature birth, abortion or still-birth
- Women health care workers need to be careful for this reason
What is late onset neonatal infection of listeria monocytogenes?
An infection that begins 2-3 weeks after birth
What is the first step in the pathogenesis of listeria monocytogenes?
Adherence and induced uptake is mediated by Internalin-A (IntA)
What happens after IntA is at play?
Listeria monocytogenes is internalized into an endycytic vacuole in the small intestine
After endocytosis occurs, what is next?
Acidification of the vacuole/phagosome by Listeriolysin O (LLO)
What does this acidification process accomplish?
It disrupts the vacuole membrane in order to allow for escape to the cytosol
This is a signal for the lysteria to release ________
Toxin
Once the listeria monocytogenes has been released into the cytoplasm and secreted toxin, what is its pathogenesis?
- Replication in host cell cytosol
- ActA mediated actin polymerization
Where can the pathogen spread to?
Neighboring cells
Blood stream
What is a disseminated infection?
An infection that gets into the blood and can spread to the liver, spleen and CNS***
How do you diagnose listeria monocytogenes?
NOT microscopy
Culture of cerebral spinal fluid and blood
Why can’t you use microscopy?
It is too insensitive
- There are too few bacteria
- Other gram positive bacteria cause bacteremia and infect the CNS
What three ways can you test the sample in culture?
- Cold enrichment selection
- Weak beta-hemolysis on blood agar
- Motility test
How do you treat listeria monocytogenes?
- Beta-lactams
- Trimethoprim-sulfamethoxazole
How do you prevent listeria monocytogenes?
- No vaccine is available
- Properly cook animal products including ready-to-eat meats
- Wash raw vegetables
Especially if the individual is immunocompromised or pregnant
For pregnant women, avoid sushi and other ready to eat meats all together
