Gram + pathogens (non spore vs spore) and toxins

Gram Stain, Morphology, and Identifying Characteristics

Listeria monocytogenes

  • Gram Stain and Morphology:
    • Gram-positive rods (coccobacilli) in pairs.
  • Growth Characteristics:
    • Grows at low temperatures (4°C and colder).
    • Tolerates a wide pH range.
    • High salt tolerance.

Corynebacterium diphtheriae

  • Gram Stain and Morphology:
    • Gram-positive, non-spore forming rods in clumps of irregular shapes.
  • Oxygen Requirements:
    • Facultative anaerobe.

Bacillus Species

  • Gram Stain and Morphology:
    • Gram-positive endospore forming rods.
  • Oxygen Requirements:
    • Aerobic or facultative anaerobes.

Clostridium/Clostridioides Species

  • Gram Stain and Morphology:
    • Gram-positive endospore forming rods.
  • Oxygen Requirements:
    • Obligate anaerobes.

Mechanism for Cell Attachment and Virulence Factors of Listeria

Attachment and Entry

  • Mechanism:
    • Internalins (proteins) bind to cell glycoproteins (cadherin) leading to internalization into M-cells and macrophages.

Key Virulence Factors

  • Escape from Phagosome:
    • Cytolysin (Listeriolysin O) – Forms pores in phagosome membranes.
    • Bacterial Phospholipase C – Breaks down phospholipids, aiding escape.

Spread Mechanism

  • Intercellular Spread:
    • ActA protein causes actin filament extension, propelling bacteria into adjacent cells.
    • Survives in migratory phagocytic cells for systemic spread.

Sources of Infection and Disease Pathology

Listeria monocytogenes

  • Common Sources of Infection:
    • Foodborne (infected milk, cheese, ice cream, peanut butter).
    • Grows at low temperatures contributing to outbreaks.
  • Disease Pathology:
    • Gastroenteritis (most common).
    • Severe outcomes: meningitis, systemic listeriosis.
    • In utero infections can lead to severe complications, including death.

Corynebacterium diphtheriae

  • Sources of Infection:
    • Respiratory droplets from carriers.
    • Oropharynx carriage occurs in many individuals.
  • Disease Pathology:
    • Causes Diphtheria: presents with respiratory symptoms and characteristic pseudo-membrane.
    • Diphtheria toxin can lead to myocarditis, paralysis, kidney failure, and systemic effects.

Toxins and Virulence Factors

Listeria monocytogenes

  • Virulence Factors:
    • Internalins (for attachment).
    • Listeriolysin O and Bacterial Phospholipase C (for phagosome lysis).
    • ActA protein (for cell-to-cell spread).

Corynebacterium diphtheriae

  • Toxin:
    • Diphtheria toxin (AB exotoxin):
    • B-portion binds to the HB-EGF receptor; A-portion terminates host protein synthesis.

Bacillus anthracis

  • Virulence Factors:
    • Protein capsule (anti-phagocytic).
    • Anthrax toxins: Lethal Factor (LF), Edema Factor (EF), Protective Antigen (PA).
    • LF+PA = lethal toxin; EF+PA = edema toxin.

Bacillus cereus

  • Toxins:
    • Enterotoxins causing food poisoning (heat-stable and heat-labile).

Clostridium perfringens

  • Key Toxins:
    • Alpha toxin (cell lysis).
    • Beta toxin (necrotizing enteritis).

Clostridioides difficile

  • Toxins:
    • Toxin A (enters intestinal cells; increased permeability).
    • Toxin B (destroys cell cytoskeleton).

Clostridium tetani

  • Toxin:
    • Tetanospasmin – AB neurotoxin affecting neurotransmitter release, causing spastic paralysis.

Clostridium botulinum

  • Toxin:
    • Botulinum toxin – inhibits acetylcholine release, causing flaccid paralysis.

Environmental Origin and Mechanisms of Exposure

Bacillus anthracis

  • Environmental Source:
    • Found in soil (herbivores).
  • Exposure Mechanisms:
    • Contact with contaminated animals/products (skin, ingestion, inhalation).

Bacillus cereus

  • Environmental Source:
    • Common in soil and grains.
  • Food Poisoning Mechanism:
    • Spores survive cooking and produce toxins post-ingestion.

Clostridium Species

  • Environmental Source:
    • Common in soil; spore-resistant.

Clostridium perfringens

  • Disease Mechanism:
    • Spores introduced through wounds; food poisoning via contaminated food.

Clostridioides difficile

  • Environmental Source:
    • Part of normal gut flora.
  • Infection Mechanism:
    • Outgrowth following antibiotic disruption of gut microbiota.

Clostridium tetani

  • Environmental Source:
    • Ubiquitous in soil.
  • Infection Mechanism:
    • Introduction through puncture wounds.

Clostridium botulinum

  • Environmental Source:
    • Ubiquitous in soil.
  • Exposure Mechanisms:
    • Improperly preserved foods, ingestion of spores (especially in infants), wound contamination.

Toxins and Physiological Outcomes

Listeria Monocytogenes

  • Toxic Mechanisms:
    • Listeriolysin O and Phospholipase C facilitate intracellular survival and spread.

Diphtheria Toxin

  • Physiological Effects:
    • Inhibits protein synthesis, resulting in local cell death and systemic organ damage.

Bacillus anthracis Toxins

  • Effects:
    • Edema and lethal toxins contribute to edema and shock; capsule protects against phagocytosis.

Bacillus cereus Toxins

  • Effects:
    • Heat-stable causes rapid vomiting; heat-labile causes diarrhea.

Clostridium perfringens Toxins

  • Mechanisms:
    • Alpha toxin leads to tissue destruction; enterotoxin causes fluid loss and diarrhea.

Clostridioides difficile Toxins

  • Mechanisms:
    • Toxin A increases intestinal permeability; Toxin B destroys cell structure, leading to inflammation and diarrhea.

Clostridium tetani and Botulinum Toxins

  • Mechanisms:
    • Tetanospasmin causes spastic paralysis (muscle overstimulation).
    • Botulinum toxin causes flaccid paralysis (loss of muscle excitability).