Study Notes on Enterobacteriaceae Family

Enterobacteriaceae Family

Overview of the Family: Enterobacteriaceae

  • Family Classification: Enterobacteriaceae-
    • Tribe Identification:
    • Escherichieae: Genus - Escherichia
      • Species: Escherichia coli (E. coli)
        • Subtypes/Pathovars: ETEC (Enterotoxigenic), EPEC (Enteropathogenic), EIEC (Enteroinvasive), EHEC (Enterohemorrhagic, aka Verotoxin-producing E. coli)
          • Associated Bacteria: Shigella, which includes S. sonnei and S. dysenteriae
    • Edwardsielleae: Genus - Edwardsiella
      • Species: Edwardsiella tarda
    • Salmonelleae: Genus - Salmonella
      • Notable Species: S. typhimurium, S. enteritidis, S. typhi
    • Citrobactereae: Genus - Citrobacter
    • Klebsielleae: Genus - Klebsiella
      • Notable Species: Klebsiella pneumoniae, K. aerogenes
    • Enterobacter: Notable Species - Enterobacter cloacae
    • Serratia: Notable Species - Serratia marcescens
    • Proteae: Genus - Proteus
      • Notable Species: P. mirabilis, P. vulgaris
    • Morganella: Notable Species - Morganella morganii
    • Providencia: Notable Species - Providencia spp.
    • Yersinieae: Genus - Yersinia
      • Notable Species: Yersinia pestis

Escherichia coli (E. coli)

  • Pathogenic Types and Their Mechanisms:
    1. Enterotoxigenic E. coli (ETEC):
      • Mechanism: Produces an enterotoxin leading to secretory diarrhea.
      • Associated Condition: Traveler's diarrhea or Montezuma’s revenge, occurring 5-15 days post-exposure.
      • Clinical Presentation: Initial attachment to intestinal epithelial cells necessary for toxin production.
    2. Enteropathogenic E. coli (EPEC):
      • Type: Invasive; exact pathogenesis unclear.
      • Target Population: Mainly affects children, causing diarrheal syndromes.
      • Pathological Reaction: Leads to inflammatory responses and breakdown of intestinal epithelial tissue.
    3. Enteroinvasive E. coli (EIEC):
      • Clinical Presentation: Feces may contain blood, mucus, and white blood cells.
      • Mechanism: Bacteria invade intestinal epithelial cells causing inflammatory diarrhea.
    4. Enterohemorrhagic E. coli (EHEC):
      • Alternative Denomination: Verotoxin-producing E. coli (VTEC).
      • Clinical Consequence: Produces bloody diarrhea due to toxin damage to epithelial cells.
      • Associated Syndromes:
        a. Hemorrhagic Colitis:
        - Symptoms: Abdominal cramps with watery diarrhea followed by bloody diarrhea; no significant fever or white blood cells noted in stool samples.
        b. Hemolytic Uremic Syndrome (HUS):
        - Clinical Significance: Leading cause of acute renal failure in children following diarrheal illness.
        - Laboratory Distinction: EHEC is the only E. coli type that is sorbitol negative; detected using MacConkey agar supplemented with sorbitol (clear colonies) whereas other E. coli ferment sorbitol (pink colonies).

Shigella spp.

  • Key Distinguishing Features:

    • Lactose Fermentation: Does not ferment lactose (glucose positive).
    • Biochemical Properties: Generally biochemically inert with most test results negative.
    • Infective Dosage: Requires only a few organisms (~100) for infection.
    • Epidemiological Correlates: Linked to poor sanitation, malnutrition, crowding, particularly noted in daycare outbreak in Indianapolis (1999).

  • Pathogenesis and Clinical Presentation of Shigellosis:

    • Mechanism: Involves fecal-oral transmission; endotoxin causing fever; enterotoxin induces intestinal inflammation and degeneration, leading to bleeding and excessive mucus secretion.
    • Symptoms: Fever, abdominal cramps, watery diarrhea, and muscle pain/myalgia.
    • Progression of Symptoms:(2-3 days manifesting)
      • Bowel movement frequency decreases; the volume of stool declines; and the feces may contain red blood cells and mucus due to epithelial damage.
    • Species Analysis:
      • S. sonnei: Milder and often asymptomatic symptoms associated with diarrheal disease.
      • S. dysenteriae: Less frequently recovered; exhibits the highest virulence, producing Shiga toxin impacting brain blood vessels, potentially leading to neurological symptoms including coma.

Salmonella spp.

Key Features and Pathogenicity

  • Pathogenesis:
    • Origin: Notable infections arise from consumption of foods/water contaminated by excrements from various animal reservoirs (e.g., poultry, cattle, pigs, pets).
    • Notable Subtypes:
      • S. typhimurium, S. enteritidis: Mostly responsible for non-typhoidal Salmonella infections; often self-limiting.
      • S. typhi:
        • Unique Reservoir: Solely human host with no natural reservoir; identified as an obligate parasite.
        • Initial Infective Dose: Between 200,000 to 1 million bacilli initiate a systemic and invasive infection resulting in intestinal ulceration and septicemia.
        • Historical Context: Example of "Typhoid Mary" - a carrier who perpetuated outbreaks without exhibiting symptoms, highlighting issues surrounding carrier states in pathogenicity.
    • Symptoms of Infection:
      • Typical febrile response: Sustained increase in fever, abdominal pain; risk of intestinal rupture and subsequent shock.

Clinical Types of Salmonella Infections

  1. Gastroenteritis:
    • Frequency: Most common type with varied diarrhea severity and accompanying low-grade fever; nausea and vomiting can occur.
    • Timeline: True infection develops across 2-3 days.
  2. Septicemia without prominent gastrointestinal symptoms:
    • Characterization: High fever and positive blood cultures indicative of systemic infection.
  3. Enteric Fever (Typhoid Fever):
    • Symptoms: Includes mild diarrhea; prolonged fever.
  4. Carrier State:
    • Long-term excretors of S. typhi post-recovery, impacting public health measures.

Citrobacter spp.

  • Key Habitat: Natural environments include soil, water, and human feces.
  • Infective Potential: Can induce urinary tract infections and septicemia, especially in immunocompromised individuals. Also associated with meningitis and brain abscesses in neonates.

Klebsiella spp.

  • Key Notes: Exhibits large mucoid colonies; lactose positive (glucose positive).
  • Types of Infections: Involves various conditions including:
    • Lung infections in patients with existing debilitating conditions (e.g., alcoholics, diabetics).
    • Other complications include urinary tract infections, enteritis, meningitis in infants, and septicemia.

Enterobacter spp.

  • Notable Species: Enterobacter cloacae - widespread in water, sewage, soil, and vegetables.
  • Pathogenicity: Typical role in opportunistic infections within urinary and respiratory tracts; not usually associated with gastrointestinal disturbances.

Serratia spp.

  • Ecology: Found in soil and water; part of normal intestinal flora.
  • Example: Serratia marcescens, known for its intense red pigmentation (prodigiosin).
  • Infection Association: Linked to pneumonia and septicemia in immunocompromised patients, and prominently nosocomial infections.

Peculiar Historical Note:

  • Serratia marcescens and its intense red pigment were historically viewed as miraculous when observed on communion wafers in the 18th century, mistaken for blood.

Proteus spp.

  • Characteristics and Motility:
    • Distinctive swarming motility; exhibits rapid population movement across agar surfaces.
    • Notable Species:
      • Proteus mirabilis: Urinary tract infections and wound infections; indicates indole negative.
      • Proteus vulgaris: Often presents indole positive; found in immunocompromised hosts.

Morganella and Providencia spp.

  • Notable species: M. morganii and Providencia spp. also predispose to urinary tract infections; other types of infections are rare.