Some considerations regarding the classification and identification of mycobacteria.
The principles of classification and identification of microorganisms are stated briefly. Reliable classification and identification are achieved by numerical methods. A simple method of testing the distinctness of taxa (clusters or species) involves three steps: determination of the hypothetical median or mean organism (HMO) for each taxon, estimation of matching coefficients (M values) for individual strains of each taxon to the HMO of the same taxon and to HMOS of other taxa, and definition of the range of a taxon as M +/- 2SD, where M is the mean M value to the HMO. The minimal number of characteristics needed for reliable classification is greater than 40, and none of the characteristics should be related or biased. A species should be defined by more than four strains. After distinct taxa are defined and named as species, new isolates are tested to determine which taxon they belong to. This test is done by a numerical method: comparison of a new isolate with the HMO of various species and testing whether the resulting M values fall within the ranges of any of these species. If an M value of a new isolate falls within the range of taxon X and M values to the HMOS of other species are outside the limits of those species, the isolate is identified as belonging to taxon X. A simple, conventional (nonnumerical) identification system consisting of a small number of tests may be used in clinical laboratories, but one should always keep in mind that identification by such a system often leads to misidentification. Causes of misidentification are false reactions (misjudgment of results), inadequate choice of test characteristics, and use of too small a number of tests.
D003951:Diagnostic Errors; D009161:Mycobacterium / Q000145:classification* / Q000302:isolation & purification / Q000502:physiology