SUMMARY: Morphological, physiological, growth and chemosusceptibility characters were determined for 80 ‘atypical’ acid-fast and 3 non acid-fast strains isolated from tuberculous, or presumed tuberculous, patients, and for 24 control strains belonging to various mycobacterial species. Overall similarity analysis was used for establishing the relationships upon the basis of 60 characters codified by 153 features.

The overall analysis differentiated five clusters having mean matching indices above 80% (80 phenon = 80P), namely: 80P-I (human and bovine mycobacteria); 80P-II (‘atypical’ mycobacteria belonging to the Ist, IInd and IIIrd Runyon groups); 80P-III (mycobacteria related to ); 80P-IV (scotochromogenic mycobacteria with greater metabolic abilities); 80P-V (). Nine strains (among which were three non acid-fast bacilli) were not included in these clusters.

The ‘atypical’ mycobacteria cluster (80P-II) was formed by three clearly delimited subgroups, which broadly corresponded to Runyon's classification.

A more detailed analysis of certain groups, and the determination of the characters of some ‘hypothetical average organisms’, allowed the further differentiation of some subgroups and aberrant strains.

The need to standardize the coding methods is stressed. Because of the value of overall similarity in such a variable genus, an international system to classify and identify strains upon a phenetic basis is suggested.


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