Bacterial gastroenteritis (Gram negative)

Question 1

Category of acute diarrhea

Answer 1

1. Non inflammatory——> watery , non bloody

2. Inflammatory————-> bloody / dysentery

Question 2

Characteristics of watery diarrhea

Answer 2

1. No red blood cells or wbc’s ——-> no inflammation
2. Usually in Large volume
3. Typically, in small intestine
4. Afebrile ( not feverish )

Question 3

Characteristics of bloody diarrhea

Answer 3

1. Both rbc’s & wbc’s are present in stool
2. Small in volume
3. Typically, in colon
4. Febrile ( feverish )

Question 4

Organisms that cause watery diarrhea

Answer 4

1. Enterotoxiogenic escherichia coli
2. Vibrio cholerae
3. Norovirus
4. Rotavirus
5. Giardia lamblia

Question 5

Organisms tyat cause bloody diarrhea

Answer 5

1. Shigatoxin - producing E.coli
2. E. Histolytica

And others

Question 6

Important properties of E.coli

Answer 6

• Facultative anaerobe
• gram-negative rods
• Ferment lactose

Question 7

What are the 3 antigens that identify E.coli ?

Answer 7

1. Somatic or “O” or “cell wall” antigen:
   * Outer polysaccharide portion of lipopolysaccharide
2. H (flagellar) antigen:
   * on flagellar protein
3. K polysaccharide (capsular) antigen

Question 8

Mode of transmission in E.coli

Answer 8

1. Colonizes vagina & urethra. From urethra, it ascends & causes urinary tract infections
2. Acquired during birth (mother’s birth canal) in neonatal meningitis
3. Fecal–oral in traveler’s diarrhea

Question 9

Habitat of E.coli

Answer 9

Human colon

Question 10

Pathogenesis of Intestinal Tract Infection: Enteropathogenic E coli (EPEC)

Answer 10

• EPEC adhere to mucosal cells of small bowel.
• After attachment, there is effacement (loss of microvilli)& formation of filamentous actin pedestals (cuplike structures)
• EPEC ——> diarrhea in infants (severe, watery non-bloody diarrhea, vomiting & fever)

Question 11

Pathogenesis of Urinary Tract Infectionsin E.coli

Answer 11

• Uropathic E. coli has pili with adhesin proteins that bind to specific receptors (dimers of galactose (Gal-Gal dimers) on urinary tract epithelium
• Motility help E. coli to ascend urethra —-> bladder —->
  ureter ——-> kidney

Question 12

Pathogenesis of Community-acquired UTI from E.coli

Answer 12

Primarily in women due to three features that facilitate ascending infection into bladder:

1- Short urethra

2- Proximity of urethra to anus

3- Colonization of vagina by members of fecal flora

Question 13

Pathogenesis of Nosocomial (hospital-acquired) urinary tract infections due to E.coli

Answer 13

• Equally in both men & women

* Associated with urinary catheters.

Question 14

Pathogenesis of systemic infection in E.coli

Answer 14

A. Capsular polysaccharide

It interferes with phagocytosis & enhance ability of E. coli to cause infections in various organs

e.g. E. coli cause neonatal meningitis have K1 capsular polysaccharide

B. Endotoxin (cell wall lipopolysaccharide)

• Causes gram-negative sepsis & septic shock; fever, hypotension & disseminated intravascular coagulation (DIC).
• Th-17 helper T cells (produce interleukin-17) are important host defense against sepsis caused by E. coli