Wound Infections

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Wound Infections

• Chapter 24

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Wound Infections

• Penetration of the skin by micro-organisms is
  difficultPart of the innate defense
• Wounds provide the most common access through the
  skin.
• Disease production in infected wounds depends on
• How virulent infecting organisms are
• How many organisms infect the wound
• Is the host immunocompetent
• Nature of the wound
• Does it contain crushed material or foreign
  material

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Staphylococcal Wound Infections

• Leading cause of wound infections
• Symptoms
• Bacteria are pyogenic
• Infection causes
• Inflammation
• Fever
• Some strains produce toxic shock syndrome
• More than 30 recognized strains

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Staphylococcal Wound Infections

• Causative Agent S. aureus
• Virulence due to the production of extracellular
  products
• Coagulase
• Causes blood clotting to evade phagocytosis
• Clumping factor
• Aids in bacterial wound colonization
• Protein A
• Hide bacteria from phagocytic cells
• ? toxin
• Produces hole in host cell membrane

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Staphylococcal Wound Infections

• Treatment
• Many strains develop resistance to antibiotics
• Many strains treated with anti ß lactamase
  penicillins and vancomycin
• Vancomycin resistant strain identified in 1997
• Epidemiology
• 30 to 100 due to patients own flora
• Factors associated with infection include
• Advanced age
• Immunosupression or poor general health
• Prolonged postoperative hospital stay

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Group A Streptococcal Infections

• Primary pathogen is S. pyogenes
• Also known as flesh eaters
• ? hemolytic, Gram-positive cocci in chains
• Can cause rapidly deteriorating disease and death
• Common cause of wound infections
• Not a lot of antimicrobial resistance early
  penicillin

• Two extracellular products are responsible for
  virulence
• Pyrogenic exotoxin A
• superantigen toxic shock
• Exotoxin B
• necrotizing fasciitis

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Pseudomonas aeruginosa Infections

• P. aeruginosa
• Major cause of nosocomial infections
• Lung infections
• Burn infections
• Community acquired infections include
• Rash and external ear infections
• Infection of foot bones
• Eye infections
• Heart valve infections
• Lung biofilms

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Pseudomonas aeruginosa Infections

• Pathogenesis
• Some strains produce enzymes and toxins to
  enhance virulence
• Exoenzyme S
• Toxin A
• Phosphlipase C
• Epidemiology
• P. aeruginosa is widespread in nature
• Prevention and Treatment
• Prevention involves elimination of sources of
  bacteria
• P. aeruginosa is multi-drug resistant
• Medications must be administered intravenously at
  high doses

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Tetanus (Lockjaw)

• Symptoms
• Divided into early and late symptoms
• Early symptoms
• Restlessness
• Irritability
• Difficulty swallowing
• Contraction of jaw muscles
• Convulsions
• Particularly in children
• Later symptoms
• Increased muscle involvement
• Pain
• Difficulty breathing
• Death

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Tetanus

• Causative Agent
• Clostridium tetini
• Anaerobic
• Gram-negative
• Bacillus
• Spore former
• 25 mortality rate rare in the developed world
• tetanospasmin toxin
• blocks inhibition of motor neurons, causing
  paralysis
• Prevention vaccination, treatment antitoxin
• Bacterial spores prevalent in dirt and dust and
  gastro intestinal tract of humans and other
  animals

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Clostridial Myonecrosis (Gas Gangrene)

• Causative Agent
• Several species of Clostridium
• Most common offender, C. perfrigens
• Encapsulated, Gram-negative bacillus
• Endospores of causative bacillus are innumerable
• Spores found in nearly all soil or dusty surface
• Normal flora of intestinal tract and vagina
• Primarily disease of wartime
• Due to neglected wounds containing debris
• Treat with hyperbaric oxygen, antibiotics
  (penicillin)

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Actinomycosis

• Causative Agent
• Actinomyces israelii
• Filamentous, anaerobic, slow growing
• Pathogenesis
• A. israelii cannot penetrate healthy mucosa
• Infection is characterized by cycles
• Abscess formation ? scarring ? formation of sinus
  tracts
• Disease progresses to skin and can penetrate bone
  or central nervous system
• Epidemiology
• Can be normal flora
• Prevention and Treatment
• No proven prevention
• Responds to numerous antibacterials
• Penicillin and tetracycline

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Pasteurella multocida

• Causative Agent
• Pasteurella multocida
• Gram-negative
• Coccobacillus
• Rounder bacillus shape
• Most are encapsulated
• Bite infections from numerous animals
• Fowl Cholera, animal reservoir
• Symptoms
• Spreading redness
• Tenderness
• Swelling of adjacent tissues
• Pus discharge

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Cat Scratch Disease

• Causative Agent
• Bartonella henselae
• Gram-negative bacillus
• Symptoms
• Disease begins within a week
• Painful enlargement of lymph nodes
• Fever
• Epidemiology
• Zoonotic disease
• Cats infected by flea bite
• Infections treated with amipicillin

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Streptobacillary Rat Bite Fever

• Causative Agent
• Streptobacillus moniliformis
• Gram-negative,Bacillus
• Symptoms
• Bite wound usually heals without complication
• Development of chills, fever, head and muscle
  ache and vomiting 2 to 10 days after healing
• Majority of cases are self limiting
• 7 - 10 of untreated cases are fatal

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Sporotrichosis AKA. rose gardeners disease

• Causative Agent
• Sporothrix schenckii
• Dimorphic fungus
• Lives in soil and on vegetation
• Associated with puncture wound from vegetation
• Sporadic
• rare in healthy people
• Untreated cases may become chronic
• Itroconazole and amphotericin B