Pseudomonas

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Pseudomonas

• Gram negative bacteria
• Rod-shaped, polar flagella (hence, motile)
• Inhabit the soil and water
• Pseudomonas aeruginosa is the most prevalent
  opportunistic pathogen
• Intrinsically resistant to many antibiotics ?
  nosocomial infection
• combinations gt2 drugs (eg. Penicillin
  aminoglycoside)

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P. aeruginosa

• Obligate aerobe
• Produce a sweet or grape-like smell
• Colonies with a fluorescent greenish colour,
• nonfluorescent bluish pigment pyocyanin
• greenish pigment pyoverdin
• dark red pigment pyorubin
• black pigment pyomelanin

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Pathogenesis

• Pili (fimbriae) promote attachment
• Exotoxin A causes necrosis, blocks protein
  synthesis (? DTx)
• P. aeruginosa is only pathogenic when introduced
  into areas of devoid normal defenses

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A 48 year old Caucasian male presented to the
emergency room after a progressive history of
left foot cellulitis. The patient works as an
oil-field worker and began experiencing left foot
erythema and blisters. -- progressed to increased
erythema and a green-yellowish drainage from the
digits and in between the toes.

• Medical history. abuse alcohol ,drug abuse when
  he was in his 20s. His family history includes
  diabetes mellitus. His x-ray report reveals no
  signs of gas in the tissue and no signs of
  osteomyelitis. His culture report revealed 3
  tiny gram negative rods and 1 gram positive
  cocci. On day 1, presumptive 4 Pseudomonas
  aeruginosa was identified. Diptheroids and
  coagulase negative staphylococcus species were
  also identified. His aerobic and anaerobic blood
  cultures were negative.In the photo on left, it
  is interesting how just his left foot is infected
  and his right foot is completely spared.
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• Discussion and Treatment
• host does not initially appear to be
  immunocompromised. However, he has a history of
  drug use and consumes alcohol quite heavily
  during the week. His work conditions are also
  conducive to these type of infections wears
  steel toe type boots and rubber-type boots in the
  field. Soil contaminates and moisture would play
  an important role in pathogenesis of this
  infection. The patient also had exposure to
  Bactrim early in his treatment which may have
  played a role in the ability of his immune system
  to fight the infection in its early stage. Two
  extracellular proteases and extracellular protein
  toxins are produced in the initial infective
  stage. Elastin protease and alkaline protease
  destroy the cells ground substance and lysis its
  supporting structure of fibrin and elastin.
  Exotoxin A has a tissue necrotizing effect and
  has the same mechanism of action as the
  diphtheria toxin. Exoenzyme S is also thought to
  be a tissue destructive exoenzyme that is
  commonly seen during pseudomonas colonization on
  burn wounds.

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The picture at left represents local colonization
of pseudomonal infection of the foot. Here, the
skin is erythematous and has a scalded-skin type
appearance. This is likely due to extracellular
toxins and proteases causing local ground
substance disruption. You can also readily see
the alginate slime layer that forms a matrix of
the pseudomonas biofilm. This alginate biofilm is
representative of pseudomonas colonization and
the bacterial attempt at protecting the colony
from host defenses. Treatment should include
primary coverage for pseudomonal infection.
Sensitivity reports revealed bacteriocidal
activity using Ciprofloxacin.
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Burkholderia pseudomallei

• Small, motile, aerobic Gram-negative bacillus
• Colonies are mucoid and smooth to rough and
  wrinkled in cream to orange colour.
• Melioidosis of humans, in SE Asia and northern
  Australia
• high mortality rate if untreated
• surgical drainage of localised infection may be
  necessary