During phenotypic characterisation of a Gram-negative aerobic bacillus in the lab, the following results are noted: oxidase positive, catalase positive, glucose oxidised but not fermented, non-motile by hanging drop, mucoid blue-green pigment on blood agar. Which organism is most likely, and which pigment is pathognomonic?
- A Acinetobacter baumannii — producing pyoverdin fluorescent yellow pigment
- B Pseudomonas aeruginosa — pyocyanin (blue-green, water-soluble) ✓
- C Burkholderia cepacia — producing blue-green violacein
- D Chromobacterium violaceum — violacein purple pigment
Correct answer: B. Pseudomonas aeruginosa — pyocyanin (blue-green, water-soluble)
Explanation
Pseudomonas aeruginosa is the archetypal oxidase-positive, non-fermenting Gram-negative bacillus that produces pyocyanin (a phenazine pigment — blue-green, water-soluble) pathognomonic of the species, combined with pyoverdin (fluorescent yellow-green). The blue-green colonies with fruity (grape-like) odour on blood/nutrient agar are characteristic. Acinetobacter is oxidase-negative. Burkholderia cepacia is oxidase-variable and does not produce pyocyanin. C. violaceum produces violacein (purple) not blue-green.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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