A Statistical Approach to the Definition of Bacterial Species

ABSTRACTA statistical method is proposed for recognition of a bacterial species or for differentiation of two groups of bacterial strains. Comparison between two groups is done by the “t”‐test. When the mean S‐values (similarity value) of two groups are A and B, and the mean S‐value for all possible combinations between strains of both groups is S, a condition necessary for defining the two groups as different species is to demonstrate the existence of equations A > S and B > S. Unless this condition is fulfilled, the two groups should be considered unseparable. The condition necessary for recognition of two groups as one species is to demonstrate the existence of equations A:= S and B = S. A few examples of the test were shown using the mycobacteria, and it was suggested that this statistical method is useful in the recognition of a species.