Evidence for the pathogenic role of Rhodococcus species in pulmonary diseases.

Three hundred expectorated sputa from patients suffering from chest disorders were examined microscopically and cultured on various media. Among other micro-organisms isolated there were four strains of Rhodococcus aurantiacus (Gordona aurantiaca), one each of Rh. erythropolis, Rh. pellegrino, Rh. rubropertinctus and Rh. rhodnii. Suspensions in 5% hog gastric mucin were virulent for immuno-suppressed white mice and the pathology of their lungs was compatible with those produced in experimental nocardial and rhodococcus infections. The in-vitro antibiogram was similar to that of Nocardia asteroides. Two of the patients from whom Rh. aurantiacus and Rh. pellegrino were isolated responded bacteriologically and clinically to treatment with co-trimoxazole. The frequency with which these rhodococci were isolated and the clinical conditions of the patients strongly indicated a pathogenic role for some Rhodococcus species. It is suggested that rhodococci should be sought in chronic pulmonary infections, particularly in those who are immuno-compromised or debilitated, and their aetiologic role determined.