Gram (-) Enteric Bacteria

Question 1

Salmonella typhi

Answer 1

Key:

• peritrichous flagella
• fecal oral transmission
• penetrate illeum epithelia and M cells
• gastric hemmorhage
• *rose spots

Extra:

• bacillus facultative
• no diarrhea
• enteric pathogenesis mediated by bacterial mediated endocytosis in enterocytes
• Peyer’s patch inflammation
• heptasplenomegaly
• immunocompromised
• Acute tx: ceftriaxone, ampicilin
• Carrier tx: TMP-SMX

Question 2

Salmonella (non-typhoid)

Answer 2

• animal food transmission (eggs)
• doesn’t penetratee beyond M cell invasion
• D/N/V
• anitbiotics increase carriage duration
• resistance from agricultural antibiotics (not misuse)

Question 3

Campylobacter jejuni

Answer 3

Key:

• curved bacillus and cephalosporin resistant (culture technique)
• most common cause of diarrhea
• childhood, 21.
• raw chicken
• Guillan Barre syndrome

Extra:

• raw chix -> ingestion -> intestine multiplcation -> intestinal injury -> Guillan Barre (immune cross-reactivity)
• bloody ulcerated intestines
• increased incidence in patients on antacids
  *

Question 4

Helicobacter pylori

Answer 4

Key:

• peptic (duodenal > gastric) ulcers, chronic gastritis
• child human -> human transmission (50% of world has this)
• (vf) VacA, CagA –> inflammatory damage

Extra:

• rare gastric cancer
• spiral or rod-shaped w/ unipolar flagella, urease vital
• VacA - tissue damage, CagA- necessary for VacA
• 80 - 90% asymptomatic

Question 5

Vibrio cholerae

Answer 5

Key:

• death within hours from dehydration
• polar flagellum w/ rapid motility
• *no invasion, enterotoxin (5 B subunits, 1 A subunit)
• rice-water stools

Extra:

• aquatic reservoir
• switch btwn metabolic and dormant states
• O blood groups more susceptible
• boil water or carbonating water is prohibitive
• B subunti bind mucosal GM1 -> A subunit activates AC -> cAMP -> block ion absorption -> water + chloride secretion

Question 6

Vibrio vulnificus

Answer 6

• Texas and Louisiana
• sepsis and wound infections
• raw oysters/shellfish, brackish water swimming, sea water wound contamination

Question 7

Escherichia coli: ETEC

Answer 7

(enterotoxigenic)

• most common diarrhea (traveler’s–short lived),
• cholera-like diarrhea,
• mannose resistant pili bowel colonization
• enterotoxins:
  
  • LT (heat labile) - cholera like (B bind to GM1, A activate AC -> cAMP -> chloride release + *inhibition of reabsorption of NaCl by villus
  • ST (heat stable) - binds to bowel receptor stimulating cGMP -> cAMP-like effects
• no tissue damage-like cholera

Question 8

Escherichia coli: EPEC

Answer 8

enteropathogenic

• only in small children
• less sever diarrhea than ETEC (short-lived)
• *EPEC Adherence Factor (EAF) adhere to small intestine brush border pilli
• no enterotoxin

Question 9

Escherichia coli: EIEC

Answer 9

enteroinvasive

• identical to shigellosis–idential invasive proteins
• contaminated food outbreaks
• invade mucosal cells -> inflammation and bloody stools

Question 10

Escherichia coli: EHEC

Answer 10

enterohemorrhagic

• all disease caused by serotype O:157 H7
• shiga-like toxin, A subunit attaches to 60S ribosome on mucosal cell -> dies -> toxin in bloodstream -> endothelial damage -> HUS (**hemolytic uremic syndrome)
• only E. coli that requires a small inoculum
• fimbrial adhesin promotes adherence to bowel mucosa, no invasion
• watery diarhea progressy to grossly bloody stool (most common cause of *bloody diarrhea)
• hamburger & milk transmission

Question 11

Shigella

Answer 11

• *bacillary dysentery
• small, non-motile that colonize colonic mucosa (no invasion into bacteremia)
• low inoculum requirement
• fecal-oral
• *mucus and blood in stools w/ intrafamily spread