Escherichia coli

Question 1

Diseases of Escherichia coli

Answer 1

1_ Urinary tract infection (UTI)
2_ sepsis
3_ neonatal meningitis
4_ “traveler’s diarrhea”

are the most common.

Question 2

Characteristics of Escherichia coli

Answer 2

1_ Facultative gram-negative rods

2_ ferment lactose

Question 3

Habitat of Escherichia coli

Answer 3

1_ Habitat is the human ((colon))

2_ it colonizes the (( vagina and urethra.))

Question 4

Transmission of Escherichia coli

Answer 4

1_ From the ((urethra)), it ascends and causes UTI.

2_ Acquired during ((birth)) in neonatal meningitis 3_ ((fecal–oral route ))in diarrhea.

Question 5

Toxines of Escherichia coli

Answer 5

1(( Endotoxin)) in cell wall causes septic shock.
2 ((Two enterotoxins )) are produced by enterotoxigenic E.coli (ETEC) strains
** The heat-labile toxin (LT)
**The heat-stable toxin (ST)
3_Shiga toxin (verotoxin) is an enterotoxin produced by E. coli strains (STEC) with the O157:H7 serotype.

Question 6

Function of The heat-labile toxin (LT) in E.coli

Answer 6

stimulates adenylate cyclase by ADP-ribosylation.

                                     ⬇️⬇️⬇️

Increased cyclic AMP causes➡️➡️ outflow of chloride ions and water, resulting in diarrhea.

Question 7

Function of The heat-stable toxin (ST) in E.coli

Answer 7

causes diarrhea, perhaps by stimulating guanylate cyclase.

Question 8

Virulence factors of E.coli

Answer 8

1_ pili for attachment to mucosal surfaces

2_ capsule that impedes phagocytosis.

Question 9

What causes of shiga toxin (verotoxin )

Answer 9

It causes :

1_ bloody diarrhea
2_ hemolytic-uremic syndrome associated with eating undercooked meat.
Shiga toxin (verotoxin) inhibits protein synthesis by removing adenine from the 28S rRNA of human ribosomes.

Question 10

What is the Predisposing factors to UTI in E.coli ?

Answer 10

1_ Predisposing factors to UTI in women include the proximity of  the  anus  to  the  vagina  and  urethra,  as  well  as  a  short  urethra.
 This  leads  to colonization of  the urethra and  vagina  by  the  fecal flora. 
2_ Abnormalities (e.g., strictures, valves, and stones) predispose as well.
3_ Indwelling urinary catheters and intravenous lines predispose to UTI and sepsis, respectively.

( Colonization of the vagina leads to neonatal meningitis acquired during birth. The main virulence factor for neonatal meningitis is the K1 capsular polysaccharide).

Question 11

The main virulence factor for neonatal meningitis in E.coli

Answer 11

the K1 capsular polysaccharide

Question 12

Which type of ager to grow E.coli on it ?

Answer 12

1_EMB (eosin–methylene blue)
2_MacConkey agar
3_TSI (Triple sugar iron)

Question 13

Characteristics of colonies on EMB

Answer 13

1_Lactose-fermenting colonies

2_Green sheen colonies on EMB agar

Question 14

What showing of e.coli on TSI ?

Answer 14

shows acid slant and acid butt with gas but no H2S.

Question 15

How to differentiate E.coli from other lactose-positive organisms ?

Answer 15

by biochemical reactions.

Question 16

Treatment of UTI caused by E.coli

Answer 16

Ampicillin or sulfonamides

Question 17

Treatment of meningitis and sepsis caused by E.coli

Answer 17

Third generation cephalosporins

Question 18

Treatment of traveler’s diarrhea caused by E.coli

Answer 18

Rehydration

Question 19

How to shorten duration of symptoms in E.coli ?

Answer 19

trimethoprim-sulfamethoxazole