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