A 92-year-old male presents with a cough of several months duration. He has been coughing up brownish "stuff." The man is 5?6? tall and his weight is down from 150 to 140 lbs., having lost 10 lbs. in the past 2 months without trying. His tuberculin skin test has been greater than 10 mm the three times you have tested him in the 25 years he has been your patient. The chest radiograph is consistent with reactivational TB. You order Mycobacterium tuberculosis testing and susceptibilities and start him on standard therapy. Luminescent real time PCR confirms M. tuberculosis. What has been the standard medium used to grow M. tuberculosis and what is the standard clue to TB in examination cases?

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Standard cultures may still be set up on Lowenstein-Jensen agar. Palmitic acid-containing broths (some with anti-TB drugs) have replaced solid agars, and growth detection systems now allow more rapid diagnosis. (The mycobacteria have limited numbers of ribosomal genes slowing their growth.) Choice B (BCYE) is a clue to legionellosis; chocolate agar is required to grow either Neisseria spp. or Haemophilus influenzae from sterile sites like CSF. Thayer-Martin is a chocolate agar with antibiotics used to culture Neisseria spp. from any mucosal surface preventing overgrowth of the normal flora. Tellurite (choice E) is a clue to C. diphtherias.

A 92-Year-Old Male Presents with a Cough of Several Months