Isolation of Avian Tubercle Bacilli in Human Silicosis

¹ Section of Bacteriology, Section of Medicine, Mayo Clinic and Mayo Foundation.

Acid-fast microorganisms with the cultural characteristics of avian tubercle bacilli were isolated from three specimens of sputum and a gastric washing from a patient with silicosis. These organisms were virulent for chickens and rabbits but failed to produce progressive disease in guinea pigs. The infected animals reacted slightly to old tuberculin but severely to avian tuberculin. Additional studies on one culture revealed it to be resistant in vitro to streptomycin, para-aminosalicylic acid and isoniazid, which is typical of avian tubercle bacilli.

The patient died of cardiac failure. Sections of lung revealed extensive pneumonoconiosis and fibrosis. Birefringent crystals typical of silica were seen in sections examined with polarized light. It is believed that the avian tubercle bacilli played little part, if any, in the production of pulmonary fibrosis and that these microorganisms were able to proliferate because of the pre-existing silicotic lesions in a host for which avian tubercle bacilli are normally relatively avirulent.