Bio 348: Gram Pos Rods

Gram Positive Rods Overview

• Introduction
  • Today’s focus: Gram positive rods
  • Review: Study guide on Gram negative rods from last session
  • Importance of understanding various gram positive rods, especially for nursing.

Classification of Gram Positive Rods

• Diverse group of organisms, categorized as:
  • Aerobic Gram Positive Rods
    • Bacillus species
      • Known for forming spores
      • Example: Bacillus anthracis (causes anthrax)
    • Corynebacterium
      • Normal flora but can cause diphtheria.
    • Lactobacillus
      • Part of normal vaginal flora.
    • Gyneorella
      • Associated with bacterial vaginosis but not covered in detail.
    • Listeria
      • Clinically significant; ability to be pathogens or contaminants.
  • Anaerobic Gram Positive Rods
    • Include numerous clinically significant species:
      • Propionibacterium
      • Cutibacterium acnes
        • Known for causing acne.
      • Bifidobacterium
      • Clostridium and Clostridioides
        • Focus on anaerobic spore formers.

Aerobic Gram Positive Rods

Bacillus Species

• General Characteristics

  • Possess endospores.
  • Morphologies include mucoid, dry, and spread-out colonies.
  • Can be environmental or clinical contaminants.

• Pathogenic Potential

  • Infection routes:
    • Through traumatic introduction can lead to cutaneous infections
    • Ingestion or inhalation of endospores
    • Risk of Bacillus anthracis (anthrax)

• Bacillus anthracis

  • Fatal if mishandled; requires proper biosafety measures.
  • Morphology resembles bamboo shoots under Gram stain.
  • Hemolysis types:
    • Nonhemolytic seen with gray colonies, needing differentiation through Gram stain.
  • Virulence Factors
    • Capsule that evades phagocytosis
    • Toxins:
      • Edema toxin (causes swelling)
      • Lethal toxin (potentially fatal)

• Clinical Manifestations

  • Cutaneous anthrax: Common form; black necrotic lesions known as eschars.
    • Typically painless but may become swollen.
  • Gastrointestinal anthrax: Rare but fatal; caused by ingestion of endospores.
  • Inhalation anthrax: Affects lungs; leads to flu-like symptoms, progresses to severe pneumonia and potentially death.
  • Injection anthrax: Associated with drug abuse; bypasses usual entry routes.

• Bacillus cereus

  • Causes food poisoning and local infections.
  • Two toxins: emetic toxin (vomiting) and other hemolysins.
  • Commonly linked to foodborne illness and should be monitored post-surgery.

Anaerobic Gram Positive Rods

Clostridium Species

• Clostridium perfringens
  • Associated with gas gangrene and food poisoning.
  • Produces gas in cultures leading to severe tissue necrosis.
• Clostridium tetani
  • Causes tetanus; characterized by lockjaw and severe muscle spasms.
  • Spores enter through wounds, particularly from rusty nails.
• Clostridium botulinum
  • Causes flaccid paralysis associated with ingestion of contaminated food (e.g., bulging cans).
  • Associated with infant botulism due to spores present in honey.

Clostridioides difficile

• Renamed from Clostridium difficile
• Causes pseudomembranous colitis, often post-antibiotic therapy.
• Diagnosed via PCR; requires liquid stool samples.
• Emphasis on hospital infection control due to high transmission risk in healthcare settings.

Non-Spore Forming Gram Positive Rods

Listeria monocytogenes

• Grows in cold environments, associated with soft cheeses and deli meats.
• Can cause meningitis, especially in pregnant women; may lead to severe outcomes like stillbirth.
• Notable for the umbrella motility shape in cultures.

Irregular Gram Positive Rods

Corynebacterium

• Exhibits pleomorphic characteristics and typical arrangements resembling “picket fences” or cuboidal shapes.
• Corynebacterium diphtheriae
  • Produces diphtheria toxin leading to severe throat infection and systemic effects.
  • Managed using vaccines and antitoxins in clinical settings.