Enterobacteriaceae I

Question 1

Are enterobacteriaceae gram+ or -?

Answer 1

NEG

Question 2

What are antibodies formed against in enterobacteriaceae?

Answer 2

O antigen of LPS

Question 3

What part of LPS is responsible for toxicity?

Answer 3

Lipid A (causes fever, diarrhea, shock)

Question 4

Where is the H antigen located?

Answer 4

peritrichous flagella

Question 5

Where is the K antigen located?

Answer 5

capsule

causes UTI, invasive disease

Question 6

What are the 7 virulence factors for enterobacteriaceae?

Answer 6

1) Endotoxins (LPS)
2) Capsule (no phagocytosis)
3) antigenic phase variation
4) type III secretory system
5) sequestration of growth factors (ex: iron)
6) resistance to serum killing
7) antimicrobial resistance

Question 7

Are enterobact obligative or facultative?

Answer 7

facultative

Question 8

What key enzyme are enterobact NEGATIVE for?

Answer 8

oxidase

Question 9

What is the energy source for enterobact?

Answer 9

ferment glucose

reduce nitrate to nitrite

Question 10

Do all bacteria ferment lactose?

Answer 10

NO, some do and some don’t

Question 11

What is special about macconkey agar?

Answer 11

only gram NEGATIVE grow on it

Question 12

What color do lactose fermenters turn on macconkey agar?

Answer 12

purple

Question 13

Is the normal flora in our body lactose positive or neg?

Answer 13

positive (streak a stool sample and if everything is purple, no infection)

Question 14

What are the 7 tribes of enterobacteriaceae?

Answer 14

I Escherichiae
II Edwardsielleae
III Salmonelleae
IV Citrobactereae
V Klebsielleae
VI Proteeae
VII Yersinieae

Question 15

What is the most common enterobacteriaceae isolated from human infection?

Answer 15

E. coli

Question 16

Where is E. coli found in the environment?

Answer 16

IT ISNT

if it is found in water, it is indicative of fecal contamination

Question 17

What are 6 clinical syndromes that E. coli can cause?

Answer 17

1) gram negative sepsis
2) UTI
3) wound infection
4) pneumonia in IC hospitalized patients
5) meningitis in neonates
6) gastroenteritis

Question 18

What are the 5 strains of E. coli causing gastroenteritis?

Answer 18

1) Enterotoxigenic (ETEC)
2) Enteropathogenic (EPEC)
3) Enteroinvasive (EIEC)
4) Enterohemorrhagic (EHEC)
5) Enteroaggregative (EAggEC)

Question 19

What strain of E. coli is associated with Traveler’s diarrhea? (profuse watery diarrhea)

Answer 19

ETEC

Question 20

What strain of E. coli is associated with infantile diarrhea?

Answer 20

EPEC (no gross blood)

Question 21

What kind of E. coli is associated with blood, mucus, and many leukocytes in the stool? And tenesmus

Answer 21

EIEC (invade epithelial cells)

Question 22

What kind of E. coli is associated with bloody diarrhea without WBCs? no fever

Answer 22

EHEC (caused by O157:H7)

Question 23

What kind of E. coli is associated with watery diarrhea with blood and mucus, less commonly associated with abdominal pain?

Answer 23

EAggEC

Question 24

What is the most common Shiga Toxin Producing E. coli (STEC)?

Answer 24

O157

Question 25

How is STEC transmitted?

Answer 25

feces of cattle, deer, sheep

humans get it via food (undercooked ground beef), water or direct contact with infected patient

Question 26

What 2 infections are associated with E.coli O157?

Answer 26

• Hemolytic Uremic Syndrome (HUS)

- Hemorrhagic Colitis

Question 27

What 3 things are indicative of hemorrhagic colitis?

Answer 27

1) abdominal cramps, watery diarrhea, bloody discharge
2) no significant fever
3) absence of WBC in stool

Question 28

What is the triad of symptoms in HUS?

Answer 28

• acute renal failure
• thrombocytopenia
• hemolytic anemia

Question 29

What is the leading cause of renal failure in kids?

Answer 29

HUS

preceded by bloody diarrhea

Question 30

What is the clinical trajectory followed by Enterohemorrhagic E. coli?

Answer 30

3-4 days nonbloody diarrhea w/ ab pain then bloody diarrhea w/ severe ab pain

either resolves in 4-10 days or HUS

Question 31

What does a CBC look like for an O157 E. coli patient?

Answer 31

RBCs are hypochromic (white) and fragmented (shisotcytes)

Question 32

What is responsible for toxicity seen in O157?

Answer 32

shiga toxin (builds up on kidney wall)

Question 33

What is the mechanism of action of Shiga toxin?

Answer 33

1) inhibit protein synthesis targets (of commensals and host cells)
2) damage microcirculation –> vasculitis –> mucosal damage
3) trigger signaling cascades (influence cytokines)
4) Hits endothelial and epithelial cells of the CNS

Question 34

What 2 settings can HUS occur in?

Answer 34

1) diarrheal related (classical)

2) non-diarrheal HUS (pneumococcal infection, chemo, transplant immunosuppression)

Question 35

What are 3 host risk factors that can increase chance of getting HUS?

Answer 35

1) young or old age
2) mental retardation
3) P antigen on RBCs (attachment site for shiga)

Question 36

Treatment with what can worsen an O157 infection?

Answer 36

anti-motility agents (increase susceptibility)

Question 37

True or false: serotypes other than O157 can cause disease

Answer 37

TRUE (still make shiga)

Question 38

What antigens are you looking for to diagnose positive O157 infection?

Answer 38

shiga
O157 antigen (LPS)

Question 39

What antibiotics do you treat STEC with?

Answer 39

NONE - will cause massive destruction of e. coli which will release all the shiga toxin and endotoxin

Question 40

How do you treat STEC diarrhea?

Answer 40

rehydration, dialysis

NO antimotility agents and NO antibiotics