Gram- Rods Causing GI Disease Flashcards
(52 cards)
What family of bacteria does this describe: short thick rods, peritrichous flagella (all around the outside), and oxidase negative?
a. Enterobacterales
b. Vibrio
c. Campylobacter
a. Enterobacterales (previously Enterobacteriaceae): short thick rods, peritrichous flagella, oxidase negative
what is the shape of Vibrio bacteria? are they oxidase positive or negative?
Vibrio: curved rods with polar flagella (flagella sticking out from one side like a tail), oxidase positive
(Gram- rod)
what shape are Campylobacter and Helicobacter bacteria?
curved or spiral shape
(Gram- rod)
what are the four 4’s of oral-fecal transmission?
Feces
Fingers
Flies
Food (& water)
M cells of intestine
specialized for transcytosis of antigens to underlying lymphoid tissue - many pathogens “hitch a ride” to exit intestine
H, O, and K bacterial antigen (used in stereotyping)
H = flagella
O = LPS
K = capsular (“kapsule”)
what is the difference in nature of intestinal infection conferred from Vibrio vs Shigella vs Yersinia? (all Gram- rods)
Vibrio and some E. coli —> bacteria secrete toxins but remain in intestinal lumen
Shigella and non-typhoidal Salmonella —> bacteria invade intestinal wall
Yersinia and S. typhi —> bacteria invade beyond intestinal wall and cause systemic infection
Which of these bacteria is most likely to cause systemic infection?
a. Vibrio
b. Yersinia
c. non-typhoidal Salmonella
d. Shigella
b. Yersinia: invades beyond intestinal wall and causes systemic infection
note these are all Gram- rods which all cause intestinal infections
a. Vibrio - secrete toxins but remain in lumen
c. non-typhoidal Salmonella and (d.) Shigella - bacteria invade intestinal wall
describe the pathology of non-invasive enteritis (name key virulence factors)
virulence factors: adhesions and exotoxins —> stimulate salt transport —> osmotic outflow of water follows —> watery diarrhea (with or without wbc)
[remember that exotoxins are deliberately secreted, vs endotoxins which are released upon lysis]
*examples: Vibrio cholerae, toxin-producing E. coli
Vibrio cholerae and toxin-producing E. coli are similar in that they both cause what kind of enteritis? (Gram- rods)
non-invasive enteritis:
virulence factors: adhesions and exotoxins —> stimulate salt transport —> osmotic outflow of water follows —> watery diarrhea (with or without wbc)
what is the specialized media that Vibrio cholerae grow on? (Gram- rod)
Thiosulfate Citrate Bile Salt (TCBS) agar - appear as bright yellow colonies on background of green (normal flora)
what is the function of the A and B subunits of Cholera toxin?
A subunit: adds ADP-ribose to Gs protein to constitutively activates it —> adenyl cyclase —> high cAMP —> high Cl- transport (via CFTR transporter) —> osmotic outflow of water into lumen —> watery diarrhea
B subunit: pentamer, mediates attachment to enterocytes
why is it thought that cystic fibrosis heterozygotes are more resistant to diarrhea from Cholera toxin (of Vibrio cholerae, Gram- rod)?
Cholera toxin is made of A and B subunit
A: adds ADP-ribose to Gs (permanently active) —> cAMP —> high Cl- transporter via CFTR —> high salt concentration in lumen pulls water out osmotically —> watery diarrhea
(B subunit mediates attachment to enterocytes)
How is enteritis from Vibrio cholerae (Gram- rod) infection treated?
fluid replacement (oral or IV) for massive diarrhea
tetracycline or ampicillin can shorten disease
name 2 non-cholera Vibrio bacteria (Gram- rods) and describe where they are found and what illness they cause
- V. vulnificus
- V. parahaemolytics
- found in natural waters
- diarrhea from eating raw fish/shellfish
- wound/soft tissue infections
- require NaCl for culture (halophiles)
- grow on TCBS medium (thiosulfate-citrate-bile salts)
what do Vibrios vulnificus and Vibrios parahaemolytics require for culture? (Gram- rods)
both are non-cholera Vibrios common in natural waters - can cause diarrhea (raw fish) and wound/soft tissue infections
halophiles: require NaCl for culture
grow on TCBS medium (thiosulfate-citrate-bile salts)
halophiles
bacteria that require NaCl for culture
what are the 3 categories of E. coli, based on differences in virulence factors?
- Enterotoxigenic E. coli (ETEC): “travelers diarrhea” (most adults immune to their own local ETEC)
- Enteropathogenic E. coli (EPEC): Type III secretion system causes cytoskeletal rearrangement, loss of brush border (“attaching and effacing lesion”)
- Shiga toxin-producing E. coli (STEC): inflammatory enteritis, hemolytic uremic syndrome (HUS)
what toxins cause disease in enterotoxigenic E. coli (ETEC)? (2)
adhere to intestinal mucosa via pili
- Labile Toxin (LT): similar to cholera toxin
- Stable Toxin (ST): structural analogue of gut peptide hormone, stimulates guanyl cyclase-coupled receptor (increases cGMP)
elevated cAMP or cGMP —> diarrhea (less severe than in cholera due to less toxin produced)
how does the severity of diarrhea from enterotoxigenic E. coli (ETEC) compare to Vibrio cholerae? (Gram- rods)
the Labile Toxin (LT) resembles cholera toxin but less is produced, so diarrhea is less severe
patients typically do not require hospitalization and intensive rehydration
describe the pathogenic mechanism of Enteropathogenic E. coli (EPEC)
adhere to surface of enterocytes, Type III secretion system exports proteins into cytosol and rearranges cytoskeleton - creates pedestal that cups bacterium produced
attaching and effacing lesion - brush border disappears (tight junctions disrupted) —> leakiness causes diarrhea (not directly toxin-mediated)
describe the pathogenesis of infection by bacteria that invade the intestinal wall (such as Shigella, Salmonella, invasive E. coli, Campylobacter)
virulence factors: adhesions, cytotoxins —> bacteria invade/kill enterocytes, induce their own phagocytosis via Type III secretion system
diarrhea from local production of inflammatory mediators (enterocytes, neutrophils) - may be bloody with wbc present
exotoxins can have systemic effects
what type of bacteria does this describe?
- infects humans only
- very low infectious dose
- almost identical to E. coli, but typically cause more severe disease
Shigella (Gram- rod)
describe the clinical manifestation of Shigella infection (Gram- rod)
Bacillary dysentery: frequent, painful, low-volume stools containing blood, WBC, mucus, cramps
