Exam VI - GI Infections Flashcards
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:
- Emetic- heat stable toxin; causes vomiting and cramps
incubation is < 6 hrs., duration 8-10 hrs.
heat stable toxin - 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
ETEC
Traveller’s Diarrhea that has two toxins
- LT1- heat labile and increases cAMP
- 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
EIEC
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
- UTI: E. coli is the #1 bacterial cause
endogenous: colon to urethra to bladder
most important virulence factor: pili for attachment - Neonatal Meningitis: via vertical transmission
- Septicemia: starts in GI tract or urinary tract then spreads to body
Salmonella
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
- 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
Shigella
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
Vibrios
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
