Although we could not co-stain for individual bacteria because of technical limitations with our staining protocol, extracellular bacilli are detected in the caseum of necrotic macaque granulomas [10] and intact acid-fast bacteria are observed in association with necrotic cells and debris in the caseum of patients with post-primary TB [20], suggesting that the signal detected from S18-2 is from extracellular bacteria in the CP-rich caseum. The gene discussed is CP; the disease is tuberculosis.