An elderly hospitalized patient with dysuria has a culture showing BAP smooth, non-hemolytic, opaque colonies; MAC colorless; CHOC growth enhanced; Gram stain shows short GNB resembling coccobacilli; oxidase negative, catalase positive (bubbles); motility non-motile; TSI K/K with no gas or H2S. Which organism is suspected?

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Multiple Choice

An elderly hospitalized patient with dysuria has a culture showing BAP smooth, non-hemolytic, opaque colonies; MAC colorless; CHOC growth enhanced; Gram stain shows short GNB resembling coccobacilli; oxidase negative, catalase positive (bubbles); motility non-motile; TSI K/K with no gas or H2S. Which organism is suspected?

This pattern points to a nonfermenting, oxidase-negative, nonmotile Gram-negative coccobacillus that grows well on chocolate agar and yields colorless colonies on MacConkey, with a nonfermentative sugar pattern on TSI (alkaline slant/alkaline butt, no gas or H2S). Acinetobacter baumannii fits all of these clues: it is oxidase negative, catalase positive, nonmotile, and often appears as smooth, nonhemolytic, opaque colonies; it grows readily on CHOC and on MAC as colorless colonies since it does not ferment lactose. The TSI result K/K confirms lack of fermentative activity. In contrast, Pseudomonas would be oxidase positive and usually motile; Klebsiella and E. coli are lactose fermenters and typically produce lactose-fermenting colonies on MAC with different TSI patterns (A/A with gas, etc.). Given the combination of oxidase status, motility, colony morphology, growth on CHOC and MAC, and the nonfermentative TSI result, the organism most consistent with this presentation is Acinetobacter baumannii.

This pattern points to a nonfermenting, oxidase-negative, nonmotile Gram-negative coccobacillus that grows well on chocolate agar and yields colorless colonies on MacConkey, with a nonfermentative sugar pattern on TSI (alkaline slant/alkaline butt, no gas or H2S). Acinetobacter baumannii fits all of these clues: it is oxidase negative, catalase positive, nonmotile, and often appears as smooth, nonhemolytic, opaque colonies; it grows readily on CHOC and on MAC as colorless colonies since it does not ferment lactose. The TSI result K/K confirms lack of fermentative activity. In contrast, Pseudomonas would be oxidase positive and usually motile; Klebsiella and E. coli are lactose fermenters and typically produce lactose-fermenting colonies on MAC with different TSI patterns (A/A with gas, etc.). Given the combination of oxidase status, motility, colony morphology, growth on CHOC and MAC, and the nonfermentative TSI result, the organism most consistent with this presentation is Acinetobacter baumannii.

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