chapter 23

Wound Infections

• Biblical Reference: Luke 10:34 mentions healing of wounds—relevant in understanding historical views of wound care.

Key Historical Figures

• Shibasaburo Kitasato (1856–1931)

  • Studied tetanus in Robert Koch's lab.

  • Identified Clostridium tetani spores in soil.

  • Demonstrated that C. tetani is an obligate anaerobe and devised cultivation methods.

  • Discovered that animals injected with C. tetani develop tetanus due to its toxin.

  • Similar work was done by Emil von Behring on diphtheria.

  • Published findings in 1890 and established an infectious disease institute in Japan.

Wound Contamination

• Common Causes:

  • Breaks in skin or mucous membranes can lead to contamination by normal microbiota or environmental microorganisms (e.g., from air, fingers).

• Factors Affecting Infection:

  • Virulence of microbes.

  • Number of microbial cells in the wound.

  • Host’s immune response.

  • Type of wound (contaminating foreign material increases risk).

Types of Wounds

• Incisions: Sharp cuts made by a knife.

• Punctures: Penetration injuries caused by sharp objects.

• Lacerations: Tearing of tissue.

• Contusions: Blunt force injuries that crush tissue.

• Abrasions: Scraping off of the skin.

• Gunshot Wounds: Caused by bullets or projectiles.

• Burns: Resulting from heat, chemicals, electricity, etc.

Anatomy and Physiology of Wounds

• Components:

  • Collagen: Main supportive protein of tissues, including scars.

  • Fibronectin: Binds tissues in healing.

  • Fibrinogen: Converts to fibrin, forms clots to stop bleeding.

• Healing Process:

  • Begins with fibroblast and capillary outgrowth to form granulation tissue, later converting to scar tissue (collagen).

Abscess Formation

• What is an Abscess?: Localized pus surrounded by inflamed tissue.

• Composition of Pus: Combination of living and dead leukocytes, tissue debris, and proteins.

• Challenges in Treatment:

  • Poor circulation hinders antibiotic delivery.

  • Treatment often requires surgical drainage.

Anaerobic Conditions in Wounds

• Anaerobic Wounds:

  • Allow growth of obligate anaerobes like Clostridium tetani.

  • Conditions may arise from contamination with dirt or deep punctures.

Consequences of Infections

• Common Outcomes:

  • Delayed healing, abscess formation, spread of toxins or bacteria, and complications in surgical wounds.

Tetanus (Lockjaw) Overview

• Symptoms:

  • Initial difficulty swallowing, jaw contractions leading to spasms and severe pain, potential respiratory issues, and risk of death.

• Causative Agent:

  • Clostridium tetani, an anaerobic, Gram-positive rod with spores.

• Pathogenesis:

  • Non-invasive but localized colonization, producing the exotoxin tetanospasmin (an A-B toxin).

  • B portion binds to motor neuron receptors, and A portion disrupts neurotransmitter release, leading to uncontrollable muscle contractions.

• Epidemiology:

  • Widespread in dirt, often enters through wounds; vaccination status plays a crucial role in disease frequency.

• Treatment:

  • Human Tetanus Immune Globulin (TIG) for passive immunity, wound care, and vaccination to prevent recurrence.

Common Bacterial Infections of Wounds

• Staphylococcal infections:

  • Staphylococcus aureus and S. epidermidis are common pathogens in wound infections.

• Necrotizing fasciitis:

  • Caused by SPE-producing strains of Streptococcus pyogenes.

• Pseudomonas infections:

  • Pseudomonas aeruginosa often infects damaged tissues, especially burns, and is highly resistant to treatments.

• Other Infections:

  • Bite wounds and soft tissue infections.

Fungal Wound Infections

• Sporotrichosis:

  • Characterized by ulcerating nodules along lymphatic vessels, caused by the fungus Sporothrix schenckii.

Summary Table of Bacterial Infections,

1. Tissue Components Exposed by Wounds:

   • Collagen: Supports tissue structure, particularly in healing.

   • Fibronectin: Binds tissues during the healing process.

   • Fibrinogen: Converts to fibrin, forming clots to stop bleeding and create a temporary barrier against pathogens.

2. Definition and Consequences of Wound Infections:

   • Wound Infections: Infections that occur when pathogens enter a wound, leading to localized inflammation and potential systemic illness.

   • Possible Consequences: Delayed healing, abscess formation, spread of toxins or bacteria, and complications in surgical wounds.

3. Common Bacterial Causes of Wound Infections:

   • Staphylococcus aureus: A predominant pathogen in wounds.

   • Streptococcus pyogenes: Known for causing necrotizing fasciitis.

   • Pseudomonas aeruginosa: Particularly found in burn wounds and known for antibiotic resistance.

4. Characteristics of Common Wound Infections Caused by Aerobic Bacteria:

   • Staphylococcal Infections:

     • Pathogen: Staphylococcus aureus.

     • Symptoms: Redness, swelling, pus formation.

   • Necrotizing Fasciitis:

     • Pathogen: Streptococcus pyogenes.

     • Symptoms: Severe pain, rapid tissue decay.

   • Pseudomonas Infections:

     • Pathogen: Pseudomonas aeruginosa.

     • Symptoms: Greenish discoloration and distinctive odor; often occurs in burn patients.

5. Conditions Favoring Anaerobic Wound Infections:

   • Deep puncture wounds or those contaminated with dirt.

   • Oxygen-deprived environments (e.g., closed spaces in tissue).

   • Presence of necrotic tissue that can serve as a nutrient source for anaerobes like Clostridium tetani.

6. Abscess Formation:

   • Potential Benefits:

     • Localizes infection, preventing the spread of pathogens.

   • Potential Harms:

     • Can cause tissue damage and may require surgical drainage for resolution. Poor circulation can hinder antibiotic efficacy.

7. Difficulties in Treating Toxin-Producing Bacterial Infections:

   • The presence of toxins can lead to rapid systemic effects (e.g., tetanospasmin in tetanus).

   • Treatment requires specialized interventions such as Human Tetanus Immune Globulin (TIG) and thorough wound care in addition to antibiotics.

8. Tetanus Overview:

   • Cause: Clostridium tetani, an anaerobic, Gram-positive rod that forms spores.

   • Pathology: Produces the exotoxin tetanospasmin; binds to motor neuron receptors disrupting neurotransmitter release, causing muscle contractions.

   • Transmission: Enters through wounds contaminated with soil.

   • Prevention: Vaccination is critical for preventing tetanus.

   • Treatment: Involves wound care, human tetanus immune globulin (TIG) for passive immunity, and vaccination to prevent recurrence.