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Micro - enterics


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H. pylori:
bacterial characteristics
*small G- spiral-shaped rods
H. pylori:
virulence factors
*urease action leads to the production of ammonia which creates an area of alkalinity
*flagella allow movement beneath mucus coat
H. pylori:
disease states
*asymptomatic carrier (50%)
*correlation with gastric cancer
H. pylori:
*antrum biopsy and culture
*C-14 urease breath test
E. coli:
general characteristics
*facultative anaerobe
What causes pathogenesis in E. coli spp?
*migration to a new area of the body
*plasmids, phages, or pathogenecity islands encoding factors
Enterotoxigenic E. Coli:
A cholera-like watery diarrhea
Describe the 2 toxins
*LT: heat labile; similar to cholera toxin but milder
*ST: heat stabile; causes increase in cGMP
What common disease does it cause?
Traveller's diarrhea
Enteroinvasive E. Coli:
Describe its mode of infection and symptoms.
*invades intestinal epithelium similar to Shigella
*abd. cramping, blood and pus in stool
Enteropathogenic E. Coli:
What common disease state does it cause?
Infant diarrhea
Describe its mode of attachment
*secretes Tir protein that inserts into epithelial cell membrane
*expresses intimin protein which binds Tir
Describe pathogenesis
*Usually doesn't penetrate the epithelium
*causes denuding of brush border
*inflammatory response may cause ulceration
What strain of EHEC causes disease?
Where is it typically found?
*the O157:H7 serotype
*it is found in cattle, beef products, and fruit and veggies that have been fertilized with tainted manure
What characteristic differentiates EHEC from other strains of E. coli?
Its inability to ferment sorbitol.
Describe the symptoms caused by EHEC.
What other disease has it been associated with?
*hemorrhagic colitis, bloody diarrhea, abd. cramping
*HUS - possibly because of specific LPS
What two factors contribute to the virulence of EHEC?
*synthesis of Shiga toxin
*low infectious dose
Decribe the vibrio cholerae bacteria.
*G- comma-shaped rod
*waterborne organism
What is the infectious dose of V. cholerae?
What does this indicate?
*high (10^8 - 10^10)
*very susceptible to low pH
What are the symptoms of infection with V. cholerae?
What is the primary tx?
Is there a vaccine?
*sudden onset of voluminous "rice-water" diarrhea w/o abd pain
*rapid rehydration, preferably PO
*a killed-cell vaccine is available
What two things mediate pathogenesis with V. cholerae?
*attachment pili
*toxin synthesis
What is the struucture of the cholera toxin?
*one A subunit, 5 B subunits
*each A subunit consists of A-1 and A-2
What is the mode of action for the cholera toxin?
*B subunits bind GM1
*A-1 enters cell and ADP-ribosylates G-protein regulator of adenylate cyclase
*increased cAMP
*Na and Cl extruded into lumen
*increased osmotic pressure drives cellular efflux of water
How is expression of the cholera toxin regulated?
*Tox-R is regulatory
*triggered by drop in pH and rise in temp.
Listeria monocytogenes:
Bacterial characteristics? Where is it often found?
*catalase +
*able to grow in high salt and low temp
*found in contaminated dairy pdts and processed meats
Listeria monocytogenes:
*invades epithelium
*uses listeriolysin O to escape vacuole and replicate in cytoplasm
*able to spread laterally like Shigella
*tropism towards placental tissue
Listeria monocytogenes:
disease characteristics
*self-ltd except in pregnant women, fetuses, neonates, and i-c pts
*SA, premature labor
*early and late onset meningitis in neonates similar to GBS
Listeria monocytogenes:
*no vaccine
*intrapartum antibiotics not shown to reduce vertical transmission
Yersinia enterocolitica:
bacterial characteristics
*G- rod
*found in humans, domesticated animals
*able to survive in contaminated water
Yersinia enterocolitica:
Symptoms? Dose?
*voluminous watery diarrhea
*mesenteric lymphadenitis mistaken for appy
*infectious dose ~10^6
*granuloma formation (rare)
*prevalent in peds
Camplylobacter jejuni:
bacterial characteristics
*G- curved rod
Camplylobacter jejuni:
How is it spread? What is the reservoir? What is the infectious dose?
*assoc. w/livestock and feed animals
*often transmitted by contaminated poultry
*no P-to-P spread
*infectious dose ~500
Camplylobacter jejuni:
*bloody, pus-filled diarrhea
*bacteremia is rare, susceptible to macrophages
*assoc. w/Guillan-Barre syndrome
Camplylobacter jejuni:
*resistance to fluoroquinolones
bacterial characteristics
*G- rod
*no non-primate reservoir
*fecal-oral transmission
*low infectious dose (10-100)
*dysentary, small-volume bloody diarrhea
*due to immune response
What kind of toxin is the Shiga toxin? What does it do?
*A+B toxin
*inhibits protein synthesis
*associated w/HUS
antibiotic resistance emerging
Salmonella enteritidis:
bacterial characteristics
*G- rod
*facultative anaerobe
*produces lg amt of H2S on TSI
Salmonella enteritidis:
What is its reservoir? What's the infectious does?
*animal and human reservoir
*infectious dose ~10^6
Salmonella enteritidis:
What's its pathogenesis? Symptoms? Communicability?
*invade GI mucosal epithelia
*rarely disseminates
*bloody, pus-filled diarrhea
*communicable throughout infxn
Describe the bacterial appearance of Salmonella Typhii. How does it stain? How does it culture?
*G- rod
*produces only a small ring of H2S on TSI slant
S. typhii has no animal reservoir while S. enteritidis does.
How is S. typhii transmitted? What is its infectious dose?
*fecal-oral route, with or without a food intermediate
*dose = 10^5
What are the steps involved in the pathogenesis of S. typhii?
*binds M cells of GI epithelia
*endocytosed and transferred to Peyer's patch
*replicates intracellularly
*passes through basal lamina
*taken up by macrophage and spread thru RES
A chronic carrier state is possible with S. typhii. What organ is notorious for sequestering the bacteria?
Gall bladder
Is there a vaccine for S. typhii?
There are 2:, attenuated PO (3 doses)
2.capsular IM (1 dose)
What is the disease course of S. typhii and what is its prognosis? What kind of drug resistance has been seen?
*fever, malaise, and flu sx
*usually self-limited in 4-6 wks
*fluoroquinolone resistance is emerging
*resistance to chloramphenicol, SMZ-TMP, and doxycycline documented

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