The  taxonomy  of bacteria  is a  contentious  subject because it  has  relied  on,  in  many  cases,  a  limited number of easily performed phenotypic tests (e.g. sugar fermentations or exo-enzyme production), and not on evolutionary criteria,  as  used in the taxonomy of animals or plants.  Consequently, micro-organisms are not infrequently moved from one group to another and given different  names, which although  intellectually stimulating for taxonomists is extremely confusing for the rest of the scientific and medical community.

With the advent of modern molecular biology this situation is changing so that comparative analysis of the genome of micro-organisms using DNA hybridization, and eventually  base sequencing,  will  allow an  objective approach. Meanwhile it is expected that fluctuations in the taxonomy of micro-organisms can be expected. The definitive  work on bacterial  taxonomy  is Bergey's Manual of systematic bacteriology, which should  be consulted for detailed information.