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Penetration of the skin by micro-organisms is difficult—Part 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
Leading cause of wound infections
Symptoms› Bacteria are pyogenic› Infection causes
Inflammation Fever
› Some strains produce toxic shock syndrome
More than 30 recognized strains
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
Treatment› Many strains develop resistance to antibiotics
Many strains treated with anti β lactamase penicillins and vancomycin Vancomycin resistant strain identified in 1997
Epidemiology 30% to 100% due to patient’s own flora
› Factors associated with infection include Advanced age Immunosupression or poor general health Prolonged postoperative hospital stay
Primary pathogen is S. pyogenes› Also known as “flesh eaters”
Β 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
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
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
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
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
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)
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
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
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
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
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
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