A 24-year-old patient with cystic fibrosis has a persistent cough; sputum culture shows Gram-negative bacilli; BAP grows after 3 days; MAC yields colorless colonies; Oxidase is positive with a purple reaction; Motility is evident; Glucose oxidation/oxidation tests: O tube yellow, F tube green; TSI is K/K. Which organism is suspected?

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Multiple Choice

A 24-year-old patient with cystic fibrosis has a persistent cough; sputum culture shows Gram-negative bacilli; BAP grows after 3 days; MAC yields colorless colonies; Oxidase is positive with a purple reaction; Motility is evident; Glucose oxidation/oxidation tests: O tube yellow, F tube green; TSI is K/K. Which organism is suspected?

In a cystic fibrosis patient, this combination of features points to Burkholderia cepacia complex. It is a non-fermenting Gram-negative rod that is oxidase positive and motile, yet does not ferment sugars. The MacConkey result of colorless colonies fits a non-lactose fermenter, and the oxidative/fermentative test showing glucose oxidation without fermentation (O tube yellow, F tube green) matches organisms that rely on oxidative metabolism rather than fermentation. The slow growth on blood agar (3 days) and the absence of acid production in the TSI test (K/K) further support a non-fermenter. While Pseudomonas aeruginosa can share several features, it typically grows more rapidly and often produces pigments, and Stenotrophomonas maltophilia is oxidase negative. Achromobacter xylosoxidans is another non-fermenter but is less consistent with this specific pattern in a CF setting. Taken together with the CF context and the risk of Burkholderia cepacia to cause persistent colonization and severe decline, this pattern most strongly indicates Burkholderia cepacia.

In a cystic fibrosis patient, this combination of features points to Burkholderia cepacia complex. It is a non-fermenting Gram-negative rod that is oxidase positive and motile, yet does not ferment sugars. The MacConkey result of colorless colonies fits a non-lactose fermenter, and the oxidative/fermentative test showing glucose oxidation without fermentation (O tube yellow, F tube green) matches organisms that rely on oxidative metabolism rather than fermentation. The slow growth on blood agar (3 days) and the absence of acid production in the TSI test (K/K) further support a non-fermenter. While Pseudomonas aeruginosa can share several features, it typically grows more rapidly and often produces pigments, and Stenotrophomonas maltophilia is oxidase negative. Achromobacter xylosoxidans is another non-fermenter but is less consistent with this specific pattern in a CF setting. Taken together with the CF context and the risk of Burkholderia cepacia to cause persistent colonization and severe decline, this pattern most strongly indicates Burkholderia cepacia.

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