A Characterization of Atypical Acid-Fast Bacilli Obtained from Patients with Pulmonary Tuberculosis

¹ Suburban Cook County Tuberculosis Sanitarium District, Hospital-Sanitarium.

The characteristics of 25 atypical and 11 typical cultures, obtained from 36 patients with pulmonary tuberculosis, were studied in terms of: 1) Colonial and cellular morphology; 2) Rate of growth in liquid medium; 3) Drug sensitivity; 4) Oxidation-reduction of dyes, catalase reaction, and neutral red tests; 5) Guinea pig virulence; and 6) The characteristics of the clinical disease encountered in these cases.

We were able to classify the atypical organisms as follows: Group I, consisting of 12 cultures which produced typical colonies and developed lemon-yellow pigmentation on exposure to light (photochromogenic); Group II, comprising three cultures which produced confluent growth with little tendency to form discrete colonies and showed no pigmentation; and Group III, consisting of 10 cultures which produced yellow-orange colonies in the dark (skotochromogenic). In general, the atypical organisms showed a rapid rate of initial growth in liquid Dubos medium, complete or partial reduction of the oxidation-reduction dyes, highly positive catalase reactions, and negative neutral red tests. Guinea pig inoculation revealed that Group I and II strains were virulent. The Group III organisms, however, were uniformly much less virulent. The atypical cultures were not markedly different from the typical strains in their sensitivity to streptomycin, PAS and isoniazid.

Review of the clinical records of the 25 patients from whom the atypical cultures were isolated, suggested certain correlations. The 15 infected with Group I and II strains all had significant pulmonary disease, clinically indistinguishable from tuberculosis caused by typical organisms, and at no time in their clinical course were cultures of typical organisms obtained. These 15 patients responded more slowly to chemotherapy than did those infected with typical strains. The 10 Group III strains all were isolated from patients with long-standing pulmonary tuberculosis who had responded satisfactorily to chemotherapy and from whom typical organisms had been recovered in sputum cultures obtained during the earlier phases of their disease. The Group III strains did not cause progressive disease in any patient. Furthermore, recovery of. Group III strains was rarely followed at a later time by the isolation of typical cultures from the same patient.