Classification of Mycobacterium simiae by means of comparative reciprocal intradermal sensitin testing on guinea-pigs and deoxyribonucleic acid hybridization.

This study is a contribution to the elucidation of the taxonomic relationships among Mycobacterium simiae serovars 1 and 2, other photochromogenic, mycobacterial species and the non-photochromogenic species M. avium and M. intracellulare. DNA-DNA homology percentages and comparative reciprocal intradermal sensitin reactions in guinea-pigs have confirmed that M. habana is a subjective synonym of M. simiae serovar 1 and that M. asiaticum is a separate species. The two strains of M. simiae serovar 2 studied were distinct from each other and both were distinct from M. simiae serovar 1. M. simiae was so different from M. avium and even from M. intracellulare serovars 12, 14, 16 and 19, that there is no basis for including M. simiae in the so-called M. avium-intracellulare complex. Neither did M. simiae bear any close relation to the photochromogenic species M. kansasii and M. marinum. A fairly close negative correlation was observed between the DNA-DNA homology percentages and the specificity differences of the sensitins from the same pairs of strains. This is per se a proof of the veracity of the two taxonomic methods used in the study.