22. Enterobacteriales 1

Enterobacteriales Order (Taxonomy)

Contains three medically vital families:

1.Enterobacteriaceae,

2.Yersiniaceae,

3.Morganellaceae.

Clinical Significance (%)

Account for 80% of significant clinical Gram-negative isolates. They cause 3/4 of UTIs and 2/3 of bacterial gastroenteritis.

Common Antigen Types

O (Somatic/LPS side chain),

K (Capsule),

H (Flagellar/Cilium).

ETEC (Enterotoxigenic E. coli)

Causes Traveler's Diarrhea (watery, non-bloody).

Virulence: LT (Heat-labile) and ST (Heat-stable) toxins.

EPEC (Enteropathogenic E. coli)

Causes Infant Diarrhea (under 1 year).

Mechanism: Attaching and Effacing (A/E) lesions and pedestal formation.

EHEC (Enterohemorrhagic E. coli)

Causes "Hamburger Disease" and bloody diarrhea.

Key complication: HUS (Hemolytic Uremic Syndrome).

EIEC (Enteroinvasive E. coli)

Causes Dysentery (similar to Shigella) by invading colonic epithelial cells using Ipa (Invasion plasmid antigens).

EAggEC (Enteroaggregative E. coli)

Causes persistent diarrhea in children.

Forms an "aggregative" (stacked-brick) attachment to cells.

LT Toxin Mechanism

ADP-ribosylation of G-protein»»» activates adenylate cyclase»»»increases cAMP»»» watery diarrhea.

Shiga-like Toxins (SLT/Stx)

Produced by EHEC; A-B type toxin that blocks protein elongation and damages endothelial cells.

A/E Lesion Virulence Factors

Requires LEE (Pathogenicity Island),

Tir (receptor),

Intimin (adhesin)

HUS Triad (Hemolytic Uremic Syndrome)

1. Hemolytic anemia

2. Thrombocytopenia

3. Acute renal failure

Shigella Movement

Uses actin polymerization to move "rocket-like" from cell to cell after invading M-cells.

EHEC Treatment Contraindication

Avoid antibiotics (especially fluoroquinolones); they trigger bacterial cell lysis and massive Shiga toxin release, increasing HUS risk.

General Diarrhea Treatment

Mostly self-limiting; focus on fluid and electrolyte replacement.

UPEC (Uropathogenic E. coli)

Most frequent cause of cystitis; requires targeted antibiotic therapy based on an antibiogram.

Nosocomial Genera

Klebsiella, Proteus, Serratia, Citrobacter, and Enterobacter. High risk of ESBL (Extended Spectrum beta-lactamase) resistance.

Proteus Diagnostic Clue

Highly motile with swarming growth on agar

Produces urease.