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Pseudomonas aeruginosa


Image Source: Doc Kaiser

General Characteristics:

  • long, thin, gram negative rod (Enterobacteriaceae are usually short and plump)
  • may be encapsulated
  • single polar flagellum
  • aerobic but can grow without oxygen if nitrate is available as a respiratory electron acceptor


Image Source: fotocommunity

Colony Appearance:

  • often beta-hemolytic
  • rough, flat, spreading colonies with ground glass appearance and serrated or jagged edges
  • aluminum foil or metallic sheen
  • blue-green pigment that diffused into the agar
  • also red or brown pigment
  • often sweet, fruity odor (grapelike or corn taco-shell-like)
  • may be mucoid
  • characteristit of cystic fibrosis (CF) patients
  • grows at 42°C
  • fluoresces under UV light

Clinical Significance: 

  • usual specimens isolated from:
    • blood
    • urine
    • sputum and other lower respiratory specimens
    • skin and wound samples
    • bone and cartilage

Pathogenesis and Infectious Disease:

  • nosocomial infections due to the use of antibiotics to which P. aeruginosa is resistant
  • exogenous infections : infections brought about by organisms in the environment
  • endogenous infections : infections brought about by organisms which have colonized the host
  • respiratory infections
  • cystic fibrosis colonizer
  • bacteremia and septicemia
  • “swimmer’s ear”
  • bacterial keratitis
  • chronic osteomyelitis
  • urinary tract infections
  • necrotizing enterocolitis in infants
  • antibiotic-associated diarrhea
  • skin and soft tissue infections
    • burn wound
    • pyoderma with large sores
    • dermatitis
    • folliculitis

Prevention and Treatmen : 

  • infection control measures
  • antibiotic therapy
    • intrinsically resistant to many antibiotics
    • antipseudomonal beta-lactam agent combined with an aminoglycoside
    • CF patients require aerosolized aminoglycoside

Test Results:

  • Lactose fermentation : negative
  • Oxidase : positive
  • Carbohydrate Utilization : oxidizes glucose, fructose, and xylose but NOT lactose or sucrose
  • Motility : positive
  • Nitrate : positive
  • Arginine Decarboxylase : positive

Other Pseudomonas species :

  • Pseudomonas fluorescens and P. putida (fluorescent group)

    • motile
    • aerobic
    • oxidase positive
    • gram negative rods
    • resembles P. aeruginosa
    • produce pyoverdin or fluorescein but not pyocyanin
    • environmental organisms
    • grows best at 25-30°C
    • nonlactose fermenting on MAC
    • lack growth at 42°C result differentiates from P. aeruginosa
    • P. putida grows at 4°C and hydrolyzes gelatin while P. fluorescens does not
    • isolated from respiratory tract specimens, pleural fluid, urine, CSF, feces, blood, and other specimens
    • associated with abscesses, UTI, sepitcemia, septic arthritis
    • nosocomial pathogen in immunosuppressed persons
  • Pseudomonas stutzeri
    • nonfluorescent gram negative rod
    • environmental organism
    • rare opportunistic pathogen
    • adherent, wrinkled or leathery, hard, dry with yellow or brown pigmented colonies on BAP
    • nonlactose fermenting on MAC
    • motile
    • oxidase positive
    • denitrifer
    • no fluorescence
    • arginine decarboxylase negative (B. pseudomallei and most common pseudomonads are positive)
    • oxidizes maltose and hydrolyzes starch
    • associated with bacteremia and septicmia, bone infection, endocarditid, eye infection, meningitis, skin infections and UTI (opportunist)
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