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Flashcards in Exam VI - GI Infections Deck (23)
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Staphylococcus aureus

cause of food poisoning if ingested (#1 cause = potato salad)- need to store food properly!
characteristics: gram +, salt tolerant, grows on MSA plate and metabolizes the mannital (carb source), which produces acid giving the yellow color on MSA
30% of population are healthy carriers (in nose)

produces enterotoxins A-E, which are heat stable
symptoms: vomiting, cramps, and sometimes diarrhea
onset: 3-6 hours, duration24-48 hours


Bacillus cereus

cause of food poisoning and gastroenteritis if ingested
characteristics: gram + rod and produces spores; produces 2 toxins:

1. Emetic- heat stable toxin; causes vomiting and cramps
incubation is < 6 hrs., duration 8-10 hrs.
heat stable toxin

2. Diarrhea- incubation >6 hrs., duration 20-36 hrs.
heat labile toxin (can be killed by heat)
main causes: meat and vegetables
increase in cAMP causes watery diarrhea just like in cholera, B. anthracis, and pertussis


Enterobacteriaceae Infections

includes E. coli (ETEC, EIEC, and EHEC), Shigella, and Salmonella
ubiquitous- found everywhere
transmission: fecal/oral
gram - rods, facultative anaerobes, ferment glucose, grow on MacConkey agar (only gram -), catalase +, and oxidase -


E. coli

mostly non-pathogenic (endogenous)
infection caused when immunocompromised or ingestion of fecal contaminated sources
Three causes of gastroenteritis: ETEC, EIEC, and EHEC



Traveller's Diarrhea that has two toxins
1. LT1- heat labile and increases cAMP
2. STa- heat stable and increases cGMP

transmission: fecal contaminated food/H2O
onset: 24-72 hours, duration: 3-5 days
symptoms: explosive watery diarrhea, cramps, fever, nausea/vomiting sometimes



rare in US, mostly in developing countries
no enterotoxin produces, instead it invades M cells
onset: 10-18 hours, duration: 3-5 days
symptoms: watery diarrhea, fever, and cramps that progress to bloody diarrhea with mucus made from the immune response leukocytes


EHEC: General Information

many serotypes, but most common is O157: H7
O = O antigen from LPS
H = flagella antigen
found in sheep, goat, and cattle GI tracts, which then spread via the fecal/oral route mostly to children
infective dose: 10-100 organisms

shiga like toxin: from phage via transduction
Stx1 & Stx2 verotoxins with 1A-5B subunit toxins that bind to 28SrRNA to inhibit protein synthesis
receptors are on intestines causing the diarrhea, and on the kidneys, which can cause renal failure
Sorbitol + whereas other E. coli strains are negative

Buzz words: undercooked hamburgers, petting zoos, unpasteurized milk/juice, lettuce, spinach


EHEC: Incubation, Duration, Symptoms, Complications, & Dx

Incubation: 3-4 days, duration: 3-7 days
symptoms: watery diarrhea that progresses to gross bloody diarrhea, severe stomach cramps, low grade fever, and sometimes vomiting

Complications: Hemorrhagic Colitis: bloody diarrhea
Hemolytic Uremic Syndrome (HUS)

Dx: collect fecal specimens ONLY
culture: Sorbitol MacConkey agar
95% E.coli- lactose +. sorbitol +
O157: H7 - lactose +, sorbitol -
directly detect shiga toxin/verotoxin or SLT genes via PCR


Hemolytic Uremic Syndrome (HUS)

5-10% of O157:H7 cases
mostly children and elderly
thrombocytopenia - decrease in platelets which cause more bleeding and bloody diarrhea
hemolytic anemia
renal failure - need dialysis for treatment, sometimes for lifetime
can cause death
Treatment: supportive care with fluids, dialysis
NO ANTIBIOTICS - this will increase toxins and progress the complications


Other E. coli Infections

1. UTI: E. coli is the #1 bacterial cause
endogenous: colon to urethra to bladder
most important virulence factor: pili for attachment

2. Neonatal Meningitis: via vertical transmission

3. Septicemia: starts in GI tract or urinary tract then spreads to body



2 species
1. S. enterica- mostly in warm blooded animals
lactose -. H2S +
over 2300 serotypes, for example:
a. typhi - typhoid fever, humans only
b. enteritidis - enteric infections and diarrhea

2. S. bongori- cold blooded animals like turtles and snakes

transmission: contaminated food/water
incubation: 12-72 hours, duration: 2-7 days
symptoms: diarrhea with mucus sometimes with blood, fever, cramps
tx: supportive care with fluids and electrolytes
virulence mech: invades M cells, destroys them, and replicates in phagocytic cells



only human reservoir; lactose -, H2S -
shigellosis: bascillary dysentery (small amount of diarrhea throughout the day with blood, pus, and mucus)

Shiga toxin: 1A-5B subunit toxins that cleave the 28SrRNA to inhibit protein synthesis; invades M cells and destroys intestinal cells and kidney cells leading to HUS

infective dose: 10 cells, so very virulent via fecal/oral
usually outbreaks in schools, day care centers, etc.
incubation: 1-4 days, duration 2-3 days
symptoms: watery diarrhea, cramps, fever, bloody diarrhea
tx: supportive care with fluids and electrolytes



Gram negative curved rod, facultative anaerobes
Marine organisms and halophiles (salt loving)
Oxidase positive

2 species:
1. Vibrio cholerae
Strains named according to O antigen
O1 El Tor, pandemic strain
2. Vibrio parahaemolyticus


Vibrio cholera

Transmission: ingestion of contaminated food or water.
Incubation 2-3 days
Organisms adhere to intestinal mucosa of small intestine and secrete cholera toxin
Cholera toxin: phage mediated, ctxA and ctxB
Presence of toxin results in massive loss of water and electrolytes
production of “rice-water stools”

Buzz words: rice water stools; huge volumes of diarrhea throughout the day that starts off brown, then goes to clear from intestinal system mucosa


Cholera Toxin

ADP ribosylates a protein that regulates adenylate cyclase in intestinal epithelial cells:
irreversibly activates the regulatory protein
activates adenylate cyclase causing cAMP to increase, which causes the cell to pump water into the intestinal lumen causing diarrhea

Disease: loss of 6L of fluid per day; can go from healthy to dead in 12 hours
60% die without treatment, which is cheap- fluids and electrolytes
worldwide there are many deaths


Vibrio parahaemolyticus

Shellfish are natural reservoirs
Ingestion of improperly cooked seafood
Oysters- main culprit
Gulf Coast
Incubation: 5-72 hours
Virulence Factor: thermostable direct hemolysin
Aka Kanagawa hemolysin, enterotxin
Induces chloride secretion by increasing intracellular calcium
Explosive, watery diarrhea (like traveler's diarrhea)
produces an enterotoxin


Vibrio Dx

Selective agar, TCBS, thiosulfate citrate bile salts sucrose agar
green agar turns orange when Vibrios grow


Campylobacter jejuni: General Information

Leading cause of bacterial gasteroenteritis in the US
virulence factors: flagella and LPS
corkscrew shape, gram negative
Microaerophilic- likes a lower amount of O2
Capnophilic- like high [CO2]
Prefers 42 degrees C; Higher temp than body temp – if campylobacter, it will survive at 37 and 42 degrees, but other ones we have learned about will only live at 37

Specialized agar containing antibiotics
Found in intestinal tract of animals (ex. chickens, turkey)
Transmission: ingestion of contaminated food, poultry, milk or water
Requires a large dose due to susceptibility to stomach acid – low virulence


Campylobacter jejuni: Complications

1.4-2 million infections/annually in U.S.
C. jejuni invades epithelium of small intestine, causes inflammation
Symptoms: bloody diarrhea, fever, abdominal pain
Associated with Guillain-Barré syndrome
Autoimmune disorder of the peripheral nervous system
Antigenic cross reactivity of LPS and gangliosides
Reactive arthritis: painful inflammation of the joints


Helicobacter pylori

Spiral shaped, but as culture ages, changes shape
Gram negative, acidophile, microaerophile, fastidious
Can live in the stomach due to urease production, which produces a cloud of ammonia that neutralized the acid
Virulence Factors: Urease and 4-6 flagella

Developing countries: 70-90% of population
Humans are the primary reservoir
Symptoms: fullness, vomiting, nausea
Higher risk: hypochlorhydria (low amounts of stomach acid) possibly caused by Nexium or tums
NO DIARRHEA because in the stomach and not the intestine
Progression over time: chronic gastritis, then peptic ulcers, and result in gastric cancer


Helicobacter pylori: Peptic Ulcer/Chronic Gastritis Formation

1. Block acid production
2. Neutralize acid with ammonia
3. Burrow into mucus
4. Attach to epithelial cells


MacConkey agar

Only gram - grows; inhibits gram + from growing
lactose +: purple/dark pink
lactose -: colorless/beige


EMB agar

Lactose fermenter: dark colonies
E. coli: metallic green sheen