E. Coli

Question 1

General characteristics of enterobacteriacea

Salmonella and E. Coli

Answer 1

Gram (-) rods

Catalase (+)

Oxidase (-)

Facultative anaerobes

Ferment glucose and sugars

• grows on MacConkey agar*
• e. Coli = pink
• salmonella = yellow/gold

e. coli specifically ferments lactose

Question 2

E. Coli specific characteristics

Answer 2

“Travelers diarrhea”
- very closely related to shigella

Characteristics:

• a-hemolytic
• motility
• lactose fermentation
• imdole (+)
• Methyl red (+)
• citrate (-)
• sulfate (-)
• urease (-)

Strains that cause enterocolitis are not normal flora, but some strains are normal flora

Question 3

EMB agar

Answer 3

Eosin-methylene blue agar

- grows e.coli specifically with blue-black colonies with metallic green shine

Question 4

E. Coli stereotypes

Answer 4

Based on O, H and K antigens

O = somatic LPS 
H = flagella protein 
K = polysaccharide capsule

Question 5

Pathogenesis of e. Coli virulence factors

Answer 5

Capsular polysaccharides
- make e. Coli slippery and difficult to phagocytosis

LPS
- are lipid A polysaccharides that produce endotoxins. This is the primary cause of shock and sepsis symptoms

Fimbrial adhesions
- allows attachment to mucosal and epithelial surfaces

Enterotoxin/shigatoxin

• causes cytotoxic and necrotizing effects
• main toxins that are secreted into the blood stream

Question 6

Enterotoxigenic E. Coli (ETEC)

Answer 6

“Travelers diarrhea” strain
- community-acquired in areas with poor sanitation

Causes watery non-bloody diarrhea

• very common in children <5 yrs
• comes from the LT/ST toxin secretions
• NO inflammation or invasion of tissues

Question 7

Enteroinvasive E. Coli (EIEC)

Answer 7

“Dysentery” form

Causes necrosis and inflammation of the intestinal epithelium since it actually invades and lysis vacuoles in the intestinal cells

Causes watery, bloody diarrhea.
- diarrhea also has mucus and leukocytes in it

Question 8

Attaching and Effacing E. Coli (AEEC)

Answer 8

Forms actin pedestals (strong attachment) by attaching to the host cell actin. Then “effaces” host microvilli

Induces premature enterocyte exfoliation and encodes for intimin and TIR
- intimin= keeps host cell attached no matter what

Has two subset forms

• EPEC (enteropathogenic)
• STEC (shiga toxin)

Question 9

EnteroPathogenic E. Coli (EPEC)

Answer 9

A subset of AEEC

“Infantile diarrhea” form
- infects children <2 the most often

Symptoms

• profuse and persistent diarrhea
• vomiting and fever
• dehydration (can be fatal if not kept in check)

Question 10

Shiga Toxin E. Coli or EnteroHemorrhagic E. Coli (STEC)/(EHEC)

Answer 10

Is a subset of AEEC
- includes O157:H7

“Shiga toxin and hemolytic-uremic syndrome form”

• causes dysentery
• causes renal failure in pediatric patients if not fixed
• can induce hemolytic-uremic syndrome after 2 weeks of infection

Question 11

What is Hemolytic-uremic syndrome (HUS)

Answer 11

Classic triad of the following

• anemia
• thrombocytopenia
• Acute kidney damage and decreased renal blood flow due to micro thrombi

Question 12

Enteroaggregative E. Coli (EAEC)

Answer 12

A type of travelers diarrhea, but not the most common one
- that being said it is very common in United States

Forms aggregate colonies/biofilms on top of cells and seeps cytotoxin and enterotoxins into cells/blood stream

Can be acute or chronic and is exceptionally dangerous to HIV patients

Question 13

E. Coli adhesions and the pathotype they are associated with.

Answer 13

EAF = EPEC

AA fimbriae = EAEC

Intimin = EPEC

Actin pedestals = AEEC

Question 14

Toxins seen in e. Coli

Answer 14

Enterotoxins

Heat-labile (LT)

Endotoxins (LPS)

Heat-stabile (ST)

Question 15

Heat-labile toxin

Answer 15

Exotoxins that are secreted by bacteria that are related to cholera

LT1: overactivates cAMP and induces hypersecretion of fluids

• watery diarrhea
• associated with K88 adhesions
• secreted by ETEC

LT2: overactivates cAMP

• induces watery diarrhea
• secreted by ETEC

Question 16

Shiga-like toxin (SLT)

Answer 16

Binds to and inactivates 60s ribosome halting protein synthesis within cells

• kills cells and removes adenine from rRNA
• produces enterocytotoxic, neurotoxic, hemorrhages, edema and thrombosis

secreted by STEC and EHEC forms

Question 17

Heat stabile toxins

Answer 17

Endotoxins that usually only releases when bacteria cells lysis

• overactivates cGMP
• hypersecretion and malabsorption of fluids = watery diarrhea and dehydration

3 subtypes:
1) STa = released by ETEC

2) STb = released by ETEC

3) EAST1 = released by ETEC/EPEC/EHEC
- enhances other toxin effects, does not produce diarrhea by itself