Chapter 18

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Chapter 18 Nonfermenting G- Rods
Miscellaneous G- Rods

• MLAB 2434 Clinical Microbiology
• Cecile Sanders Keri Brophy-Martinez

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General Characteristics of Nonfermenters

• Nonfermentative organisms that break down
  carbohydrates oxidatively (aerobically) are also
  called oxidizers or saccharolytic
• Organisms that are NOT able to break down
  carbohydrates fermentatively or oxidatively are
  called biochemically inert or nonoxidizers

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General Characteristics of Nonfermenters (contd)

• Nonfermenters are ubiquitous in the environment
• Also isolated in hospitals from nebulizers,
  dialysate fluids, saline, and catheter devices
• Somewhat resistant to disinfectants

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Nonfermenter Clinical Infections

• Nonfermenters make up 15 of all isolates of g-
  rods
• Some common disease manifestations and risk
  factors for nonfermenters
• Disease manifestations
• Septicemia
• Meningitis
• Osteomyelitis
• Wound infections following surgery or trauma

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Nonfermenter Clinical Infections (contd)

• Risk factors for nonfermenter infection
• Immunosuppression
• Foreign body implantation
• Traumatic break in a host barrier

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Biochemical Characteristics of Nonfermenters

• Nonfermenters vary in biochemical and morphologic
  characteristics
• All are nonreactors on TSI slants
• Oxidative vs. fermentative properties can be
  demonstrated with use of OF (oxidative/fermentativ
  e) medium

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Initial Clues to Nonfermenters

• Long, thin g- rods or cb
• Oxidase positive (not ALL nonfermenters)
• Nonreactive in 24 hours on commercial kit systems
• TSI nonreactive
• Resistant to antibiotics

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Nonfermenter Organization

• Nonfermenters are grouped according to three
  characteristics
• Growth on MacConkey
• Oxidase reaction
• OF test

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Commonly Encountered Nonfermentative Organisms

• Pseudomonas characteristics
• G- rods or cb
• Usually motile with polar or polar tufts of
  flagella
• Oxidase and catalase positive
• Usually grows on MacConkey agar
• Usually oxidizes carbohydrates

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Commonly Encountered Nonfermentative Organisms
(contd)

• Pseudomonas aeruginosa
• Most common nonfermenter isolated from clinical
  specimens
• Not common as normal flora
• Types of infections
• Bacteremia with ecthyma gangrenosum of skin
• Wound infections
• Pulmonary disease (esp. in Cystic Fibrosis)

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Commonly Encountered Nonfermentative Organisms
(contd)

• Types of Infections for P. aeruginosa (contd)
• Nosocomial UTI
• Endocarditis
• Meningitis
• Otitis externa (swimmers ear)
• Hot tub syndrome
• Virulence factors for P. aeruginosa
• Endotoxins, hemolysins, proteases, slime, etc.

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Commonly Encountered Nonfermentative Organisms
(contd)

• P. aeruginosa identifying characteristics
• Beta-hemolytic on blood agar
• Green metallic sheen due to production of pigment
  pyocanin (green)
• Most strains also produce pigment pyoverdin
  (blue)
• Odor described as grape-like or Frito-like

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Commonly Encountered Nonfermentative Organisms
(contd)

• P. aeruginosa P. aeruginosa
• on MacConkey producing procyanin

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Commonly Encountered Nonfermentative Organisms
(contd)

• Pseudomonas fluorescens Pseudomonas putida
• Produces pyverdin but not pyocyanin
• Rarely causes clinical disease
• Stenotrophomonas maltophilia
• Third most common nonfermenter cultured
• Common in the hospital environment

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Other Nonfermenters

• Acinetobacter found in hospital environments
  can cause opportunistic infection
• Pseudomonas stutzeri wrinkled, leathery
  colonies that may be light yellow or brown
• Burkholderia cepacia most often associated with
  pneumonia in Cystic Fibrosis
• Burkholderia pseudomallei causes melioidosis
• Alcalingenes found in water and resistant to
  disinfectants