A 62-year-old male smoker admitted to hospital develops pneumonia with hyponatraemia and deranged liver enzymes. Urinary antigen testing is positive. Which culture medium is required for primary isolation of the causative organism?
- A Lowenstein-Jensen medium incubated at 37 degrees Celsius
- B Buffered charcoal yeast extract agar supplemented with L-cysteine and iron salts ✓
- C MacConkey agar with sorbitol replacing lactose
- D Thiosulphate citrate bile salts sucrose agar
Correct answer: B. Buffered charcoal yeast extract agar supplemented with L-cysteine and iron salts
Explanation
Legionella pneumophila causes atypical pneumonia associated with hyponatraemia, relative bradycardia and gastrointestinal symptoms. It is a fastidious organism requiring buffered charcoal yeast extract agar supplemented with L-cysteine and iron salts; it will not grow on ordinary media because it needs cysteine as an essential nutrient. Sorbitol MacConkey agar is used for Escherichia coli O157:H7, Lowenstein-Jensen for mycobacteria, and TCBS agar for Vibrio cholerae.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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