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Nonfermentative Bacilli

General Characteristics:

  • prefer wet environments
  • not usually part of healthy human normal flora
  • most are environmental organisms (including the hospital environment)
  • considered opportunistic and can colonize and infect immunocompromised individuals
  • often found as transient or colonizing flora of healthcare-associated pathogens

Common Group Indicators:

  • organism does not ferment carbohydrates
    • nonfermenters produce weak acids from oxidation of the sugars present.
    • these weak acids cannot be detected on TSI agar so there is no color change on the slant or in the deep butt
    • a subtle pink color on the TSI slant is due to the deamination of the proteins present by the organism which is a typical reaction for nonfermenters
  • nonfermenters can be oxidase positice
  • nonfermenting gram-negative rods show poor growth on MacConkey agar
  • some have sweet, fruity odors and display unique colony morphologies and pigmentation
  • many are often multi-drug resistant
  • display limited biochemical reactivity in commercial identification systmes used for Enterobacteriaceae

Biochemical Tests:

  •  Hugh-Leifson Oxidation-Fermentation (OF) Medium
  • Oxidase
  • Decarboxylation of Amino Acids
    • control tube does not turn yellow as it does with the Enterobacteriaceae because nonfermetners are unable to ferment the glucose present.
    • a positive reaction is a deeper purple color as compared to the gray-purple control
  • Growth at 42° C
  • Pigments, colony morphologies, and distinct odors
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