Exam VI - GI Infections Flashcards
(23 cards)
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
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
- Block acid production
- Neutralize acid with ammonia
- Burrow into mucus
- 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
