Wound Infections

Skin Infections

  • Breaks in skin or mucous membranes allow microorganisms to enter.
  • Infection results depending on:
    • Virulence of microbes
    • Number of microbial cells in wound
    • Host’s immune system
    • Type of wound

Common Bacterial Infections of Wounds

Staphylococcal Wound Infections

  • Signs and Symptoms:
    • Staphylococcus are pyogenic, causing pus production.
    • Inflammatory reaction (redness, swelling, pain, heat).
    • Fever if infection is large or spreads to blood and lymph.
    • Toxic shock syndrome from toxin-producing strain: high fever, muscle aches, life-threatening drop in blood pressure, shock.
  • Causative Agents:
    • Staphylococcus aureus, Staphylococcus epidermidis
    • Facultative anaerobes; thrive on dry salty skin
    • S. aureus most common cause of wound infections
    • S. epidermidis can cause device-associated infections
  • Transmission:
    • Survive well in environment and are easily transferred via direct and indirect contact.
    • S. epidermidis usually part of normal microbiota; opportunist in immunocompromised individuals.
    • S. aureus carriers have increased risk for surgical wound infection.
    • Found in microbiota of some individuals: skin, upper respiratory tract
  • Treatment and Prevention:
    • Often difficult due to antibiotic resistance.
    • Methicillin-resistant S. aureus (MRSA) resists multiple antibiotics.
    • Vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) have emerged.
    • Thorough cleaning of wounds reduces infections.

Group A Streptococcal “Flesh-Eating Disease”

  • Severe infections can progress rapidly and are very invasive.
  • Spread into tissues and organs, causing:
    • Pneumonia
    • Meningitis
    • Streptococcal toxic shock syndrome
    • Necrotizing fasciitis (“flesh-eating disease”)
  • Signs and Symptoms:
    • Severe pain at wound site.
    • Rapid progression, sometimes within hours, with swelling, stretching, and discoloring of the skin.
    • Fever and confusion develop.
    • Without immediate treatment: shock and death may follow quickly.
  • Causative Agent:
    • Streptococcus pyogenes
    • Enzymes destroy subcutaneous fatty tissue and fascia.
    • M protein causes neutrophils to release inflammatory molecules; also helps avoid phagocytosis.
    • Virulent strains produce damaging streptococcal pyrogenic exotoxins.
    • Superantigens inducing inflammation by non-specific activation of helper T cell, release cytokines.
    • Protease causing tissue destruction and breakdown.
  • Transmission:
    • Bacteria enter through abrasions and immune system can’t fight it off.
    • Risk factors: skin wounds (trauma, burns, surgery), chronic diseases (diabetes, alcoholism), weakened immune system (cancer, AIDS, injected-drug abuse).
  • Treatment and Prevention:
    • Generally easy to treat: susceptible to penicillin.
    • Toxins spread rapidly: immediate debridement often essential to remove dead tissue and reduce pressure; amputation may be necessary to remove source of toxins.
    • Combination of intravenous antibiotics given with supportive care.
    • Vaccines against M proteins being tested in animals.

Pseudomonas aeruginosa Infections

  • Opportunistic pathogen and significant cause of healthcare-associated infections.
  • Signs and Symptoms:
    • Characteristic greenish pus.
    • After entering bloodstream: chills, fever, skin lesions, shock.
  • Causative Agent:
    • Pseudomonas aeruginosa: Gram-negative rod with polar flagellum.
  • Transmission:
    • Pseudomonas aeruginosa widespread in nature, grows in most places with moisture.
    • Sources: Soaps, ointments, eye drops, contact lens solutions, cosmetics, disinfectants, swimming pools, hot tubs, even distilled water.
    • Introduced into hospitals on ornamental plants, flowers, fruit baskets.
    • Not allowed in burn wards or intensive care units.
    • Also found on hospital equipment, soles of shoes, illegal injectable drugs.
  • Treatment and Prevention:
    • Resistant to many antibiotics; form biofilms that increase resistance to treatment.
    • Only a few antimicrobial medications effective, and not against all strains.
    • Sensitivity tests determine most appropriate medication.
    • Intravenously high dosed medication necessary for systemic infections.
    • Eliminate possible sources of infection; treat wounds promptly; remove dead tissue from burn wounds; apply antibacterial cream.

Diseases Due to Anaerobic Bacterial Wound Infections

  • Many wounds are relatively anaerobic (lacking O2), allowing growth of obligate anaerobes such as Clostridium tetani.
  • Due to extensive tissue damage, small but deep punctures, or contamination with dirt.

Tetanus (Lockjaw)

  • Signs and Symptoms:
    • About a week after infection: irritability, difficulty swallowing, muscle stiffness (often starting in the jaw).
    • Then continuous, painful, uncontrollable muscle spasms.
    • Breathing becomes difficult, abnormal heart rhythms may occur, bones can fracture; severe pain.
    • Death often follows lung damage from pneumonia or regurgitation of stomach contents.
  • Causative Agent:
    • Clostridium tetani
    • Anaerobic, Gram-positive, rod-shaped; forms spherical endospores at one end of cell.
    • Exotoxin tetanospasmin (AB toxin) released from cells.
    • Binds to motor neurons and blocks release of inhibitory neurotransmitters that allow muscle relaxation.
    • Causes spastic paralysis (uncontrolled contraction).
  • Transmission:
    • C. tetani widespread in soil and dust, also in gastrointestinal tract and feces of those who have eaten endospore-contaminated food.
    • Anaerobic puncture wounds: stepping on a nail, body piercing, tattooing, animal bites, splinters, injected-drug abuse, insect stings, also surgery; abrasions, and burns if anaerobic due to dirt, dead tissue.
    • Individuals who get tetanus have inadequate immunity, either not immunized, or missed scheduled booster shot.
  • Treatment and Prevention:
    • Thoroughly cleaning all wounds of dead tissue and foreign material that could cause anaerobic conditions.
    • Vaccine (DTaP) contains inactivated tetanospasmin.
    • Also includes diphtheria toxoid and acellular pertussis (whooping cough) vaccine.
    • Booster given every 10 years.
    • Human tetanus immune globulin (TIG) injection
    • Antibodies bind to toxin molecules, provide passive immunity, but do not neutralize attached tetanospasmin or repair nerve damage.
    • Muscle relaxants and supportive care necessary.
    • Antibacterial kills actively growing C. tetani cells.

Clostridial Myonecrosis (“Gas Gangrene”)

  • Signs and Symptoms:
    • Severe pain, swelling, and fluid leaks from wound; may look frothy (gas production).
    • Incubation period: 1–5 days.
    • Tight skin becomes mottled with black as tissue dies.
    • Near death, victim becomes delirious and goes into coma.
    • Rare but life-threatening.
  • Causative Agent:
    • Clostridium perfringens most common.
    • Encapsulated, Gram-positive, spore-producing, anaerobic, rod-shaped.
    • Releases gases as a product of fermentation.
    • Gases increase pressure and aid spread of infection.
  • Transmission:
    • C. perfringens widespread in soil, common in intestinal tract of animals and humans; sometimes in vagina of healthy women.
    • Gas gangrene occurs in neglected wounds and occasional surgical wounds; in uterus after self-induced abortions, occasionally after miscarriages or childbirth.
    • Blood vessel disease or diabetes (poor oxygenation of tissue) are predisposing factors.
  • Treatment and Prevention:
    • Prompt debridement of all dead and infected tissue; perhaps amputation.
    • Antibiotics, perhaps hyperbaric oxygen treatment.
    • No available vaccine.

Fungal Wound Infections

Sporotrichosis (“Rose Gardener’s Disease”)

  • Signs and Symptoms:
    • Resemble those of a bacterial skin infection, often leading to misdiagnosis.
    • Chronic localized forms, usually within 1 to 3 weeks.
    • Series of ulcerating nodules that develop toward center of body.
    • Lymph nodes enlarge, but patients generally do not become ill unless immunocompromised.
    • Death is rare; painless.
  • Causative Agent:
    • Sporothrix schenckii
    • Dimorphic fungus that switches between single cellular (yeast-like) to multicellular (mold) life stages.
    • Found in soil and moss.
  • Transmission:
    • Conidia (reproductive spore) enters through injury.
    • Mostly associated with puncture wounds from plant material; farmers, carpenters, gardeners.
    • Can be transmitted by infected animals.
  • Treatment and Prevention:
    • Antifungal medications.
    • Prevention includes wearing protective gloves and clothing.

Review Questions

  • Pseudomonas aeruginosa causes:
    • Greenish pigment in wounds
  • Popular name for tetanus is:
    • Lockjaw