Transcript Wound Infections

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
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Restlessness
Irritability
Difficulty swallowing
Contraction of jaw muscles
Convulsions
 Particularly in children
› Later symptoms
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Increased muscle involvement
Pain
Difficulty breathing
Death

Causative Agent
› Clostridium tetini
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
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