Lecture 20. GI Infections 1

Diagnostic value of fecal and Gram's stain for GI microflora for GI infections

Little diagnostic value.

Gastroenteritis

Nausea, vomiting, diarrhea, and abdominal discomfort.

Diarrhea

Abnormal fluid-like fecal discharge from disease of the small intestine.

Dysentery

Inflammatory disorder of the GI tract with blood/pus in feces, fever, and cramps due to large intestine disease.

Enterocolitis

Inflammation of both the small and large intestines.

Morphology and oxygen requirement of E. coli

Facultative anaerobic Gram-negative rod.

E. coli

what pathogen is indicated by the gram negative rods in this image

E. coli classification

1. Based on serology (O, H, F, K antigens)

2. pathology (ETEC, EPEC, STEC, EIEC).

ETEC infection establishment

Normal flora--> Entry via fecal-oral route → adherence to intestinal mucosa via fimbriae → toxin-mediated hyper secretion

fimbriae

what virulence factor is shown by this ETEC causing E. coli

pathogenesis of ETEC

fimbriae and enterotoxin mediated pathogenicity that results in toxin mediated hypersecretion (no damage to GI epi)

Fimbrial virulence factors in ETEC

1. F5 in calves and lambs

2. F4 in pigs.

Enterotoxins produced by ETEC

1. Heat-labile (LT)

2. heat-stable (ST) toxins (Sta in calves, STb in piglets).

what leads to ETEC in neonates

They experience FPT (failure of passive transfer) and can't block fimbriae binding.

What is the result of fimbriae binding to intestinal epi and enterotoxin release

Stimulate adenylate cyclase → inhibit Na⁺/Cl⁻ uptake in villi → increase Cl⁻ secretion in crypts → ↓ absorption.

Clinical signs of ETEC infection

1. Watery/yellow-white diarrhea (calf scours)

2. dehydration

3. hypovolemic shock

4. high mortality in 3-5 days.

Diagnosis of ETEC

1. Clinical signs + history

2. Latex agglutination for fimbriae

3. multiplex PCR for virulence factors.

are fecal cultures used in ETEC diagnosis

No, unless done on fresh feces before antibiotics.

Treatment of ETEC

1. IV fluids/electrolytes

2. antibiotics for septicemia

3. immunoglobulins for FPT.

Prevention of ETEC

Sanitation, adequate colostrum, dam vaccination, oral passive monoclonal antibodies.

Virulence factors for EPEC

Pili and intimin (eae); no toxin production.

Virulence factors for STEC

Shiga toxins, fimbriae, and Stx2e toxin (especially in piglets).

Pathogenesis of EPEC/STEC

Bind to intestinal epithelium → hypersecretion + malabsorption (THERE IS CELL DAMAGE OF A/E LESIONS)

Disease associated with STEC in piglets

Edema disease (increased vascular permeability, no cell damage).

Diarrhea in EPEC/STEC infection is...

Rare.

Diagnosis of EPEC/STEC

1. PCR for Shiga toxins, 2. histology for A/E lesions.

attaching and effacing lesions (Cell damage) in the intestines is associated with what E. coli types

EPEC and STEC

Key feature of EIEC pathogenesis

Invasion of intestinal epithelial cells in humans.