BACTERIAL TAXONOMY BACTERIAL TAXONOMY 1. Classification: Arrangement of bacteria into taxonomic groups on the basis on biochemical, physiological, genetic, and morphological properties. 2. Nomenclature: Naming of taxa according to their characteristics. 3. Identification: For identification of an unknown taxon and to isolate and identify the causative agent of a disease. BACTERIAL CLASSIFICATION • Cavalier and Smith’s Classification (1998) - Most accepted system. • Molecular classification, six kingdoms—Bacteria, Protozoa, Chromista, Plantae, Fungi and Animalia. BACTERIAL CLASSIFICATION Principle Used to Classify Bacteria Mainly three approaches: 1. Phylogenetic 2. Adansonian 3. Molecular. Phylogenetic Classification • Hierarchical classification representing a branching tree-like arrangement Phylogenetic Classification • Characteristics which are given importance are: o Morphology of bacteria—cocci or bacilli o Staining property - gram-positive and gram-negative o Cultural characteristics such as lactose fermenting and non-lactose fermenting colonies o Biochemical reactions, e.g. coagulase positive Staphylococcus and coagulase negative Staphylococcus. o Antigenic structure, e.g. antigenic structure of somatic antigen present in bacterial cell wall. Adansonian Classification (phenetic classification.) • Classifies organisms based on giving equal weight to every character o • Numeric taxonomic system using algorithms like cluster analysis. Molecular Classification • Based on the degree of genetic relatedness of different organisms. • Guanine + cytosine (G + C) content of bacteria is estimated after extracting DNA from pure bacterial culture. NOMENCLATURE • Branch of taxonomy, that is concerned with designating scientific names to taxa. • Bacterial nomenclature is based on binomial nomenclature as proposed by Swedish botanist Carolus Linnaeus. Binomial nomenclature • Scientific names for taxonomic levels above genus - always capitalized but not italicized; for example, Phylum Proteobacteria. • Scientific name comprises of a genus name (starts with a capital letter) and species name. • Both genus and species should be written in italic or are underlined; e.g. Staphylococcus aureus or Staphylococcus aureus. • Genus is usually a Latin noun. • Species refers to a defined taxon of organisms within a particular genus. Binomial nomenclature • The genus and species are coined based on some property of the bacteria. o Staphylococcus aureus - Staphyle means bunch of grapes, and aureus meaning golden yellow. o Neisseria meningitides - discoverer (U. Neisser) and disease (meningitis) o Brucella suis and Brucella melitensis - discoverer (David Bruce) and animal host (pig) and the place of discovery (Malta, Europe). Taxonomic name changes of medicallyimportant microorganisms Type Cultures • International reference laboratories which are designated as type culture reference centers. o ATCC (American Type Culture Collection), USA o NCTC (National Collection of Type Cultures), UK.