MBI 405 Exam 3 || Already Graded A+.
Vibrio cholerae correct answers Gram negative comma-shaped & flagellated rods. 2
chromosomes, pH sensitive, halophilic, oxidase +. 2-3d incubation; produces rice water stools
with dehydration (sunken eyes and cool skin). Electrolyte imbalance leads to muscle cramps. CT
is a complex A-B toxin; A subunit translocates to ADP ribosylate the Gs subunit. cAMP levels
rise, leading to water loss. Quorum sensing influences expression of virulence. At low density
LuxO-P activates sRNAs that target HapR, turning virulence on. At high density LuxO is
dephosphorylated. HapR is transcribed, turning virulence off to create an exit strategy. Other
pathogens cause explosive diarrhea, headache, cramps, malaise, fever, chills, and necrotizing
fasciitis-type lesions.
Salmonella Typhi correct answers Small Gram negative rods, highly motile with peritrichous
flagella. Common GI inhabitant. Facultative anaerobes, reduce nitrate, ferment glucose, lac -,
oxidase -. High fever within first week, headache, muscle pains, diarrhea or constipation. Second
week brings high fever, delirium, and rash. Convalescent at third week.
Salmonella enterica correct answers Small gram negative rods. Enteric species. Gastroenteritis
12-36h post infection; mild diarrhea, nausea, fecal leukocytes, fever. Can lead to septicemia,
which includes anorexia, anemia, and rare secondary lesions.
ETEC correct answers Enteric species. Watery to cholera-like diarrhea, pediatric in developing
countries. Known as traveler's diarrhea. Has LT and ST; binds to small intestine with CFA pili.
EPEC correct answers Enteric species. Watery diarrhea, largely in infants. Loose binding with
BFP, injects TIR with T3SS. Intimate binding with intimin-TIR interaction. Actin
polymerization leads to pedestal formation.
EAggEC correct answers Enteric species. Watery to mucoid diarrhea. Binding by aggregative
fimbriae with the production of one or more toxins. Secretion of mucus and biofilm formation.
Shigella correct answers Enteric species with large invasion plasmid. Watery diarrhea to
dysentery. Diarrhea contains pus and blood. Leads to tenesmus and small/mucoid bowel
movements. Can cause HUS. Binds and trancytoses M cells; phagocytosed by macrophages.
Escape phagosome and use actin based motility to push into neighboring cell. Shiga toxin
cleaves A residue at 28S rRNA; blocks protein elongation (EF-1).
EIEC correct answers Enteric species. Watery diarrhea to dysentery. Same MO as Shigella.
STEC correct answers Enteric species. Cramps and diarrhea, can lead to hemorrhagic colitis and
HUS. Same MO as EPEC but produces Shiga toxin.
Campylobacter correct answers Gram negative curved rod; highly motile with
polar/amphitrichous flagella. Darting motility. Can cause septicemia (C. fetus) with
hematogenous spread from GI tract. Sequelae include Guillan Barre syndrome and reactive
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