CLASSIFICATION AND NOMENCLATURE OF MYCOBACTERIA

Abstract

1. Numerical classification of mycobacteria
The numerical classification introduced to the field of microbiology by Sneath was first applicated by Bojalil and his associates to the study of mycobacteria. However, the number of characters used by them remained 30. It was much less than 50 which were considered as appropriate to obtain reliable results (Sneath; Lockhart). The present author carried out numerical classification first using a large number of characters. As the result of this study, the genus Mycobacterium was divided into two subgenera, which approximately corresponded to slowly growing mycobacteria and rapidly growing mycobacteria. The subgenera were divided by the following characters: (1) growth rate; (2) tolerance to picric acid; (3) tolerance to nitrite; (4)-(6) utilization of succinate, malate and fumarate as sole carbon source.
According to the results of our studies, the following taxa were regarded as independent species:
A. Slowly growing mycobacteria. M. tuberculosis, M. bovis, M. kansasii, M. marinum, M. gastri, M. simiae, M. asiaticum, M. xenopi, M. gordonae, M. avium-intracellulare-scrofulacaum complex, M. nonchromogenicum, M. triviale, M. shimoidei, M. szulgai.
B. Rapidly growing mycobacteria. M. smegmatis, M. phlei, M. fortuitum, M. chelonei (M. chelonei subsp. chelonei), M. abscessus (M. chelonei subsp. abscessus), M. thermoresistibile, M. vaccae, M. chitae, M. parafortuitum, M. rhodesiae, M. obuense, M. agri, M. aichiense, M. chubuense, M. gilvum, M. duvalii.
Among the above, M. nonchromogenicum, M. thermoresistibile, M. chitae, M. parafortuitum, M. obuense, M. rhodesiae, M. agri, M. shimoidei, M. chubuense and M. aichiense were proposed by Tsukamura or Tsukamura and his associates. M. szulgai was proposed by Marks, Jenkins and Tsukamura in 1972.
2. Tests useful for differentiation among mycobacteria
(1) Tests useful for differentiation of M. tuberculosis and M. bovis from other mycobacteria: (a) salicylate medium, (b) para-nitrobenzoic acid medium.
(2) Tests useful for differentiation between slowly growing and rapidly growing mycobacteria: (a) picric acid (0.2%)-Sauton agar, (b) nitrite (0.1%)-Sauton agar.
(3) Test useful for differentiation between pathogenic and non-pathogenic species of Group II and Group III mycobacteria: ethambutol (5μg/ml)-Ogawa egg medium.
(4) Tests useful for differentiation of M. fortuitum, M. chelonei and M. abscessus from other mycobacteria: (a) PAS degradation test, (b) salicylate degradation test.
(5) NH₂OH · HCl-Ogawa egg medium (0.125, 0.25 and 0.5mg/ml).
(a) No growth at 45°C and growth on NH₂OH (0.5 mg/ml) show that the test strains belong to either M. fortuitum, M. chelonei or M. abscessus. Hence, all pathogenic ones of Group IV are distinguished by these characters.
(b) M. xenopi and M. gastri of Group III are susceptible to 0.25 mg/ml NH₂OH, whereas M. avium complex and M. nonchromogenicum complex are resistant to this.
(c) M. kansasii is susceptible to 0.25 mg/ml whereas M. marinum is resistant to it.