Enteric Bacteria Flashcards
Shigella bacteriology
- gram stain and shape
- fermentation
- mobility
- respiration
- intra vs extracellular
gram (-) rods non-lactose fermenting and not H2S producing -non motile -facultative anaerobe -facultative intracellular
If you have a GI infection, what is going to be the general bacteriology (stain)? What is the exception? What is the general respiration?
Gram (-) bugs; Listeria is the exception; facultative anaerobic
On culture, how can you distinguish between shigella and e. coli?
E coli ferments lactose (bright pink on MacConkey), shigella does not
Shigella Pathogenicity
- disease names (3)
- infectious dose
- presentation
- mortality risk
- complication
shigella enterocolitis, bacillary dysentery, and shigellosis
- very low (~100 IUs)
- bloody diarrhea, local inflammation, ulceration
- worse with poor nutrition
- Reactive Arthritis (Reiter’s syndrome)
Reactive Arthritis
“Can’t see, can’t pee, can’t climb a tree.”
- associated w/ HLA-B27
- conjuctivitis, urethritis, and arthritis
- shigella and chlamydia
Shigella pathogenesis
- target
- cause of presentation
- immune evasion
- populations most at risk
- invade epithelium of distal ileum and colon and secrete exotoxins
- exotoxins kill adjacent cells
- necrosis, apoptosis, host immune response and hemorrhage lead to bloody diarrhea
- survive phagocytosis and cause macrophage apoptosis
- children under 5, HIV+, MSM
Main Shigella virulence factor
- seen in what other bacteria?
- secretion system
shiga toxin: protein-synthesis-inhibiting shiga toxin is plasmid-encoded
- can be picked up by E coli
- type 3
Hemolytic uremic syndrome
begins when shiga toxin escapes into bloodstream, causes hemolysis, renal failure, uremia, and DIC
Dx Shigella: Exam
Very young/very old: fever, dehydration, severe headache, lethargy, watery diarrhea w/ bloody mucous
Dx HUS: Exam
hemolysis, thrombocytopenia, uremia requiring dialysis
Dx Shigella: Lab
Strain via immunoassays (agglutination); methylene blue stain of fecal sample to determine if neutrophils are present (Shigella, salmonella, campylobacter)
Dx HUS: Lab
schistocytes, decreased platelets, increased PMNs, increased lactate dehydrogenase
Shigella treatment
fluids/elect replacements; ceftriazone, fluoroquinolone, azithromycin, cefixime; NO antidiarrheal meds
Shigella prevention
sewage disposal, water chlorination, handwashing
E. coli bacteriology
- stain and shape
- fermentation
- respiration
- mobility
- straight gram (-) rod
- lactose fermentor, H2S/urease negative
- facultative anaerobe
- may be mobile (flagella) or nonmobile
E. coli pathologies (6)
- enterotoxigenic diarrhea
- enterohemorrhagic diarrhea
- UTI
- meningitis
- pneumonia
- intra-abdominal escape after GI perforation
Enterotoxigenic E coli (ETEC)
Traveler’s diarrhea
Enteropathogenic E coli (EPEC)
childhood diarrhea
Enteroinvasive E coli (EIEC)
causes shigella-like dysentery
Enterohemorrhagic E coli (EHEC)
infected by phage STX, produces shiga toxin, causes hemorrhagic colitis or HUS
Enteroaggregative E coli (EAggEC)
primarily associated w/ persistent diarrhea in children in developing countries
Enteroadherent E coli (EACE)
cause of childhood diarrhea and traveler’s diarrhea in Mexico and N. Africa
Enterotoxigenic diarrhea pathogenesis
- pili attach to jejunum and ileum
- enterotoxins (exotoxin that acts on the GI tract)
- enterotoxin LT forces host ion channels to export, host loses fluid, potassium, and chloride
Enterohemorrhagic diarrhea pathogenesis
- attach to mucosal epithelial cells of the colon and may invade
- lysogenic phage STX encodes shiga toxin which becomes active inside gut cells, shuts down protein synthesis, destroys some
- inflammation, bloody diarrhea
- if toxin hits blood stream > HUS