Classification and taxonomy
With the advent of molecular techniques the distinction among evolutionary identification and classification relationships has become blurred. In bacteriology a classification is simply a technique of organizing information. This organization may have an underlying meaning or no meaning at all. We could choose to classify bacteria on the color their colonies have when grown on agar plates a classification which would give prominence to the few red and yellow colored bacteria through the majority would be classified in a group of white to cream colony forms. In past microbiology, organisms were classified according to shape, with the bacillus shape now also called a rod forming the largest group and cocci, filaments, and many smaller ones. It is important to stress which classifications were arbitrary; moreover, they do still have a use presently. Microbiologists classify organisms according to their growth properties.
The basic means of classification in microbiology in common with the rest of biology is the Linnaean system. This is a hierarchical system with major divisions sequentially separated down to the lowest level species. The full classification of Escherichia coli is Bacteria (kingdom), Prokaryota (domain), l-proteobacteria (class), Pro- teobacteria (phylum), Enterobacteri- aceae (family), coli (species), Escherichia (genus) and Enterobacteriales (order). Each of these levels is define as a taxon (plural taxa). This system of classification allows biologists a unique identification
Figure:The full Linnaean system of classification.
across all the kingdoms and domains solely through using the appropriate species and genus. The full name of E. coli is its taxonomy and the Linnaean system is a taxonomic classification.In this text the correct domain and kingdom names are used to denote both the Archaea and Bacteria (prokaryotes). Slightly older systems give the kingdom names as Archaeabacteria and Eubacteria (true bacteria), which in many ways is slightly more descriptive.