E.coli

Question 1

Classification

Answer 1

Family: Enterobacteriaceae
Genus: Escherichia
Species: Coli

Survive for months in the soil and water

Question 2

Morphology

Answer 2

Gram negative rods

Motile

Question 3

Growth characteristics

Answer 3

Facultatively anaerobic

Nonfastidious

Ferment lactose
- this distinguishes it from shigella and Salmonella

Question 4

Antigenic structure

Answer 4

O antigens
K antigens
H antigens
> 1000 antigenic types (serotypes)

Particular sero types are associated with various diarrheal diseases:

O157:H7 causes hemorrhagic colitis

Question 5

Virulence factors

Answer 5

Adhesins- pilli

Capsule:
Capsular Ag K1 -> similar to the embryonic form of the polysialic acid of the neural cells

E.coli K1 strains -> causative agents of neonatal meningitis

Exotoxins:
Enterotoxins (heat labile and heat stable)

Invasiveness

endotoxins

Question 6

Disease

Answer 6

Two groups:

-intestinal infections (gastroenteritis)

-extraintestinal infections
(Most common):

UTI (80% of community acquired)
Septicemia
Neonatal meningitis (infants < 1 month)
Would infections (postoperative)
Intraabdominal infections 
Biliary tract infections 

BUSWIN

Question 7

Virulent types of pathogenic E.coli

Answer 7

• enteropathogenic E.coli (EPEC)
• enterotoxigenic E.coli (ETEC)
• enteroinvasive E.coli (EIEC)
• enterohemorrhagic E.coli (EHEC)
• enteroaggregative E.coli (EAggEC)

P T I H A

Question 8

• enteropathogenic E.coli (EPEC)

Answer 8

Affect small intestine

Destroy epithelial cells

Diarrhea in infants < 3 years:

• fever
• nausea
• vomiting
• non-bloody diarrhea

Question 9

enterotoxigenic E.coli (ETEC)

Answer 9

Affect small intestine

Produce HL and HS enterotoxins

Traveler’s diarrhea

Infant diarrhea in underdeveloped countries:

• watery diarrhea
• vomiting
• cramps
• nausea

Question 10

enteroinvasive E.coli (EIEC)

Answer 10

Affect large intestine

Invade and destroy epithelial cells

Dysentery-like diarrhea

• fever
• cramps
• initial water diarrhea -> dysentery with bloody stools

Question 11

enterohemorrhagic E.coli (EHEC)

Answer 11

Produce shiga-like toxins

Affect large intestine

Destroy epithelial cells

Hemorrhagic colitis

Hemolytic uremic syndrome

Question 12

enteroaggregative E.coli (EAggEC)

Answer 12

Affect small intestine

Prevent fluid absorption

Infant diarrhea in underdeveloped countries

• persistent watery diarrhea
• vomiting
• dehydration

Question 13

Microbiological diagnosis

Answer 13

Specimen:

Stool

Culture:

Differential medium (Mac Conkey’s, EMB agar):
- Lactose-positive colonies, metallic sheen

Biochemical tests:

Motile
Ferment lactose
Ferment glucose
Indole positive

Serologic tests:

Rapid slide agglutination test

Question 14

Treatment

Answer 14

Treatment of extraintestinal infections:

• susceptibility testing is obligatory
• active antimicrobials:
  > broad-spectrum penicillins
  > 2nd and 3rd generations of cephalosporins
  > fluoroquinolones

ESBLs -> treatment with carbapenems

Treatment of gastroenteritis

• fluid and electrolyte replacement
• antimicrobial therapy
  > fluroquinolones (ciprofloxacin, norfloxacin)
  > TMP/SMX
  > abroad-spectrum penicillins

Question 15

Prevention

Answer 15

No vaccine

Prevention of UTIs (prompt removal of catheters)

Prevention of septicemia:

• prompt removal of catheters
• switching of the site of catheters

Prevention of traveler’s diarrhea
- prophylactic use of TMP/SMX or Norfloxacin