Micro Enteric Bacteria 1

Question 1

shigella bacteriology

Answer 1

• gram -, oxidase - rods
• not lactose fermenting
• not H2S producing
• nonmotile
• facultative anaerobes and facultative intracellular
• human-restricted
• fecal-oral

Question 2

how to distinguish lactose fermenter from non lactose fermenter

Answer 2

MacConkey medium - fermenters will be bright pink

Question 3

shigella infectious dose

Answer 3

very low ~100IUs

Question 4

what does shigella typically cause?

Answer 4

bloody diarrhea, local inflammation, ulceration

Question 5

what complications are there a risk for with shigella?

Answer 5

1. reactive arthritis (Reiter’s Syndrome - can’t pee, can’t see, can’t climb a tree)
2. HUS

Question 6

what is a sign of a poorer prognosis with shigella?

Answer 6

malnourished child (esp with vit A and zinc deficiencies)

Question 7

Reactive arthritis autoimmune?

Answer 7

HLA-B27

Question 8

shigella virulence factors

Answer 8

1. shiga toxin - plasmid borne
   - toxin causes cell necrosis, apoptosis, inflammatory response, and hemorrhage for bloody diarrhea
2. siderophores
3. type III secretion system

Question 9

siderophores

Answer 9

iron-chelating moles that allow the bacteria to parasitize enough iron to grow to large numbers

Question 10

how does shigella invade?

Answer 10

enters through M cells and infects macrophages - goes into epithelial cells backwards and sideways to infect neighboring cells causing a local infection

Question 11

how is entry of shigella mediated?

Answer 11

type III secretory system

Question 12

how does shigella cause HUS?

Answer 12

shiga toxin escapes into blood stream setting off an immunologic/hematologic cascade leading to acute hemolysis, uremia, DIC

Question 13

diagnosis of shigella

Answer 13

physical: fever, dehydration, severe headache, progression from watery to bloody diarrhea
lab: agglutination, methylene blue (neutrophils) stain of fecal matter
* *usually affects very old or very young

Question 14

diagnosis of HUS caused by shigella or E. coli

Answer 14

check blood for schistocytes, decreased platelets, increased PMNs, increased lactate dehydrogenase

Question 15

shigella treatment

Answer 15

rehydrate, antibiotics if warranted but NOT if suspecting E Coli!!!, HUS dialysis and supportive care, NO antidiarrheal meds

Question 16

e coli bacteriology

Answer 16

• straight gram - rod
• facultative anaerobe
• lactose fermenter
• H2S negative, urease negative
• may be mobile or nonmobile
• normal GI fauna

Question 17

e coli pathologies

Answer 17

1. enterotoxigenic diarrhea
2. enterohemorrhage diarrhea
3. enteropathogenic, enteroaggregative, enteroinvasive diarrheas
4. UTIs
5. meningitis
6. pneumonia

Question 18

is E coli intracellular or extracellular?

Answer 18

EXTRACELLULAR (have fimbriae for adherence or Type III or IV secretion system) with the exception of EIEC which is like shigella with actin-based cell to cell motility

Question 19

e coli gastroenteritis

Answer 19

• water diarrhea
• bacteria use fimbrae to attach to gut lining
• enterotoxins force hot cells to release fluids, potassium

Question 20

e coli bloody gastroenteritis

Answer 20

• bloody diarrhea
• bacteria adhere to gut lining with some tissue destruction
• strains carrying Shiga plasmid which becomes active inside gut cells, shutting down protein synthesis, destroying some, and causing inflammation
• if toxin reaches bloodstream, risk of HUS

Question 21

risk of HUS

Answer 21

shiga toxin in EHEC

Question 22

Enterohemorrhagic E coli (EHEC) pathogenesis

Answer 22

includes O157:H7 - carries shiga toxin gene which halts host protein synthesis and kills infected cells causing a bloody diarrhea with 9-30% proceeding to HUS (acute renal failure, microangiopathic hemolytic anemia and thrombocytopenis)

Question 23

what is EHEC associated with?

Answer 23

antibiotics to treat bloody diarrhea

Question 24

what happens when shiga toxin hits the bloodstream?

Answer 24

Gb2 receptor activated, nephrotoxicity, capillary occlusion (fibrin-platelet thrombi in renal microvasculature), cytokine dysreguation (esp vWF, TNFalpha, IL1, IL6), kidney failure with lactate dehydrogenase marker

Question 25

diagnosis e coli

Answer 25

pink on MacConkeys (lactose fermenter), bloody or nonbloody diarrhea, dehydration, recent travel abroad check for HUS

Question 26

e coli treatment

Answer 26

self-limited, rehydrate | EHEC: give NO antimotility agents and antibiotics associated with increased HUS risk

Question 27

staph aureus food poisoning

Answer 27

gastroenteritis caused by toxin secreted by staph aureus in room temp food -onset is fast - intoxication process only takes hours (infectious process would take at least a day)

Question 28

foodborne botulism

Answer 28

gastroenteritis and descending flaccid paralysis caused by neurotoxin secreted by clostridium botulinum into airtight-packed food -onset is fast (not as fast as staph)