4. E. coli Shigella

Enterobacterales and Escherichia coli

  • Presenter: Tibor Pál

  • Affiliation: Department of Medical Microbiology and Immunology, University of Pécs, Hungary

Overview of Enterobacterales

  • Also known as "enteric bacteria"

  • Found in the gastrointestinal tract, plants, and environment

  • Comprises of over 60 genera

  • Medically significant for its roles in:

    • Urinary tract infections (UTIs): 50-80%

    • Hospital-acquired pneumoniae: 20-25%

    • Bloodstream infections: 15-30%

  • Notable genera:

    • Escherichia (includes Shigella), Salmonella, Yersinia, Proteus, Morganella, Klebsiella, Enterobacter, Citrobacter, Serratia

Characteristics of Enterobacterales

  • Primarily composed of Gram-negative rods

  • Possess LPS (lipopolysaccharides) - endotoxin that can cause shock

  • Multi-resistance tendencies

  • Structure includes:

    • Outer membrane

    • Cell membrane

    • Cytoplasm

  • Antigens:

    • O antigen (LPS) is always present (except Yersinia pestis)

    • K antigen (capsule) presence varies by species/strain

    • H antigen (flagellum) presence varies by species/strain

Escherichia coli (and Shigella)

  • E. coli is a standard member of the gut flora

  • Antigenic variations: O:(K+/-):(H+/-)

  • Pathogenic potential varies significantly across strains

  • Shigella is genetically close to E. coli - traditionally classified as a separate genus due to specific pathogenicity traits

Types of E. coli Infections

  • E. coli can be categorized as:

    • Apathogens: Normal intestinal flora

    • Extraintestinal Pathogenic (ExPEC) strains:

      • Involved in enteric infections, causing diarrhea and other systemic infections

      • Uropathogens (UPEC) responsible for UTIs

      • Neonatal Meningitis (NMEC)

  • Strains related to diarrhea-causing pathotypes include:

    • Enteropathogenic E. coli (EPEC)

    • Enterohaemorrhagic E. coli (EHEC)

    • Enterotoxigenic E. coli (ETEC)

    • Enteroaggregative E. coli (EAEC)

    • Enteroinvasive E. coli (EIEC)

ExPEC Virulence Factors

  • Include:

    • Siderophores: Iron-chelating compounds

    • Cytotoxins

    • Fimbriae: Various types (type 1, P, S, M) aiding adhesion

    • Surface proteins: Include ibeA, traT, afa/dra

    • Toxins: Include cytotoxic distending toxin (CDT) and cytotoxic necrotising factor (CNF)

    • Capsule (K1, K5, ...): Functions to evade phagocytosis

Pathogenesis of Urinary Tract Infections (UTIs)

  • Community-acquired UTIs: 70-80% caused by E. coli

  • Predominantly affects women due to anatomical proximity and shorter urethra

  • Infections usually ascend from the colon to the urethra and bladder

  • Cystitis Mechanism:

    • Type 1 fimbriae adhere to uroplakin (mannose) leading to cell invasion,

    • Inflammation causes cell detachment which can be detectable in urine

  • Pyelonephritis involves specific adhesins (e.g., P fimbriae) and toxins leading to kidney infections

Asymptomatic Bacteriuria

  • Strains may lose virulence factors but can form biofilms, prompting treatment when seen in children and pregnancy

Bloodstream Infections

  • Derived from pyelonephritis or gut bacteria through mucosal barrier injuries

  • Increased risk in neonates and patients with intestinal perforations or other infections

Neonatal Meningitis (NMEC)

  • Major cause of neonatal meningitis associated with K1 capsular antigen

  • Mechanism includes blood-brain barrier transcytosis, leading to infection and inflammation in the brain

Diarrhea-causing Pathotypes of E. coli

  • Types include:

    • EPEC: Causes watery diarrhea; adhesion disrupts absorption

    • EHEC: Shiga toxin-producing, associated with severe complications like HUS

    • ETEC: Common in developing countries; causes watery diarrhea through enterotoxins

    • EAEC: Chronic diarrhea in children; linked to malabsorption

    • EIEC/Shigella: Causes dysentery, severe inflammation, and ulceration

Summary of Pathogenic Characteristics and Treatment Approaches

  • EPEC: Affects primarily children under 3; management involves rehydration and sometimes antibiotics.

  • EHEC: Low infectious dose, foodborne transmission; management focuses on supportive care.

  • ETEC: Human reservoirs, often food-related; supportive measures are key, with limited antibiotic use.

  • EAEC: Not well understood epidemiology; treatments may include rehydration.

  • EIEC/Shigella: More severe; treatment may include antibiotics and electrolytes.

Further Readings and Contact Information

  • Reference: Murray, P., Rosenthal, K., Pfaller, M. (eds.): Medical Microbiology, 8th ed. 2015 Elsevier

  • Contact: pal.tibor2@pte.hu