Enterobacteriaceae I

Question 1

Characteristics of Enterobacteriaceae

Answer 1

Facultative Gram Neg Rods
Ferment Glucose
No Oxidase
simple growth requirements- blood agar
LPS Endotoxin
Reduce nitrate to nitrite

Question 2

What are the components of LPS?

Answer 2

O Antigen: outer most element-> gives many serotypes; Antibodies are against O polysaccharides

Lipid A: Innermost region of LPS leading to toxicity and septic shock when released into blood

Question 3

Where are H and K antigens located?

Answer 3

H Antigen: In the peritrichous flagella

K Antigen: Capsule

Question 4

Which Enterobacteriaceae do NOT ferment lactose?

Answer 4

Salmonella
Shigella
Proteus
Yersinia

Question 5

Which Enterobacteriaceae ferments lactose?

Answer 5

E.Coli
Klebsiella
Enterobacter
Citrobacter
Serratia

Question 6

What is MacConkey Agar good for?

Answer 6

Selective fro gram negative growth and doesn’t allow gram positive growth

Can make diffferential as well by putting latose and checking for lactose fermenting ability
Purple: lactose fermenter
Colorless: non lactose fermenter

Question 7

What are the main genera of Enterobacteriaceae?

Answer 7

E.coli
Shigella
Edwardsiella
Salmonella
Citrobacter
Klebsiella
Enterobacter
Serratia
Proteus
Yersinia

Question 8

Where is E.coli normally found?

Answer 8

Instestines of humans and animals

Question 9

How does Ecoli grow on Macconkey Agar?

Answer 9

purple: Lactose fermenter

Flat

Question 10

What is Ecoli most know for clinically?

Answer 10

Common cause of UTI

Number 1 cause of meningitis in neonates

Question 11

What are clinical sx of E.coli infection?

Answer 11

Gram Neg Sepsis
UTI
Wound infections
Pneumonia
Neonatal meningitis
Gastroenteritis

Question 12

What are the different strains of Ecoli causing gastroenteritis?

Answer 12

ETEC: enterotoxigenic
EPEC: enteropathogenic
EIEC: Enteroinvasive
EHEC: hemorrhagic
STEC: Shiga Toxin producing
EAggEC: Enteroaggregative

Question 13

What is characteristic of ETEC?

Answer 13

Enterotoxigenic E.Coli
Due to secretory toxins that do not damage mucosal
Secretory diarrhea -> profuse and watery
AKA Traveler’s Diarrhea

Question 14

What is characteristic of EPEC?

Answer 14

Enteropathogenic
Adheres to epithelial cells -> attaching and effacing lesions
Occurs in infants -> infantile diarrhea with mucous but no blood

Question 15

what is characteristic of EIEC?

Answer 15

Enteroinvasive
invades epithelial cells -> inflammatory diarrhea (like dysentery in shigella) with blood mucus and leukocytes
Hallmarks: Fever and colitis

Question 16

What are the characteristics of EHEC/STEC?

Answer 16

Enterohemorrhagic/Shiga Toxin Producing

Genes to produce shiga toxins -> E.Coli O157:H7 mainly -> bloody diarrhea without WBCS
No fever
Can lead to Hemolytic Uremic Syndrome

Question 17

What are the characteristics of EAggEC?

Answer 17

Enteroaggregative

Adhere to epithelial cells -> watery diarrhea with blood and mucus

Question 18

A college student returning from a Spring vacation in Puerto Vallarta, Mexico developed a profuse watery diarrhea accompanied by mild abdominal cramps. His diarrhea is so profuse that he is experiencing symptoms of dehydration. While on vacation he was careful not to purchase food from street vendors but did frequent the local bars and had drinks served with ice. Stool exam revealed no blood or WBC’s. What type of diarrheagenic E. coli is most likely to cause the symptoms
experienced by this student?
A. E. coli O157
B. Enterotoxigenic E. coli (ETEC)
C. Enteroinvasive E. coli (EIEC)
D. Enteropathogenic E. coli (EPEC)
E. Enterohemorrhagic E. coli (EHEC)

Answer 18

B

Question 19

Which strain of E.coli is most identified wiht producing Shiga Toxi?n

Answer 19

E.Coli O157/STEC

Question 20

How is E.coli O157 transmitted?

Answer 20

Shed in feces of animasl -> contaminated food or water

Also direct contact with infected patietn

Question 21

Where is the reservoir of E.coli O157?

Answer 21

Healthy dairy cattle -> Ground beef in hamburgers

Question 22

What is HUS?

Answer 22

Hemolytic Uremic Syndrome:
Acute Renal Failure
Thrombocytopenia
Hemolytic Anemia

Precedes bloody diarrhea -> only about 20% with infection get HUS

Question 23

What is the clinical sequence of sx for EHEC?

Answer 23

3-4 days nonbloody diarrhea with abd pain => onset of bloody diarrhea with severe abd pain => resolution in 4-10 days
OR
HUS => death or long term sequelae (renal impairment, HTN, CNS)

Question 24

Do the E.coli O157 organisms cause infections by invading bloodstream?

Answer 24

NO
Stay in intestines-> secrete Shiga toxins into blood -> bind to receptors on endothelial cells (renal endothelial area have large conc of receptors) => RENAL FAILURE

Question 25

How do the shiga toxins work?

Answer 25

Inhibit protein synthesis in commensal bacteria and host cells
Damage microcircultion -> vasculitis -> mucosal damage-> blood diarrhea
Induce cytokines and apoptosis

Question 26

What are the risk factors for developing HUS after EO157 infection?

Answer 26

Very young/old age

P Antigen on RBCs

Question 27

How is EO157 detected?

Answer 27

Anigens: Shiga Toxin or O157 LPS antigen
Direct fecal specimen detection
Enriched broth culture detection

Question 28

How is STEC diarrhea treated?

Answer 28

Oral rehydration
Dialysis for HUS/Renal Failure
NO ABX!!! => destroy Ecoli cells -> massive release of ST and endotoxin all at once-> potentiation -> bad for patient

Let it play out and manage sx

Question 29

A healthy 3-year-old child develops diarrhea that lasts about a week, and that is bloody for a few days. His diarrhea resolves, but he remains lethargic, and passes only a little urine. A blood
smear shows fragmented red blood cells and no platelets. What etiologic agent of infection would most likely produce the signs
and symptoms displayed in this case?
A. E. coli 0157
B. Campylobacter jejuni
C. Salmonella typhi
D. Shigella flexneri
E. Yersinia enterocolitica

Answer 29

A