Lec.1 Classification and grouping of bacteria 2025 - Copy.pdf

Classification and grouping of bacteria Prof. Dr. Lamyaa Kadhim Baqer Medical Bacteriology  Learning objectives The learning Objectives of this lecture are: 1-Define the taxonomic models 2- Explain grouping of bacteria 3-Clarify the taxonomy techniques 4- Determi...

Classification and grouping of bacteria Prof. Dr. Lamyaa Kadhim Baqer Medical Bacteriology  Learning objectives The learning Objectives of this lecture are: 1-Define the taxonomic models 2- Explain grouping of bacteria 3-Clarify the taxonomy techniques 4- Determine the classification systems  Taxonomy Microbial taxonomy is the science that studies micro-organisms in order to arrange them into groups or taxon. Taxonomy consists of three separate but interrelated parts 1- Classification: Is the arrangement of organisms into groups or taxa (singular, taxon) using specific shared characteristics. 2- Nomenclature: Is naming of taxonomic groups according to rules so that it means the same to all microbiologists. 3- Identification: Is the practical use of classification to determine that a particular isolate belongs to a recognized taxon. Is classification and identification important in medical practice ? Medical practitioner needs to isolate, identify and find antibiotic susceptibility of a certain pathogen patients with infections. Microbiology treatment often is exceptionally difficult when the pathogen is unknown. Your text here Genus - The hierarchical classification system consists of the following taxa designations: Example: Taxonomic Ranks of the bacterium Escherichia coli Prokaryotes evolved before eukaryotes The three –domain system , based upon molecular analysis ,prokaryotes are divided into two domains bacteria and Archaea Prokaryotes -Are single-celled organisms -May be single-celled or multicellular organisms -Genetic material is not contained in -Genetic material is contained inside a a distinct nucleus distinct nucleus - Have membrane-bound organelles, which - Have no membrane-bound carry out specific cell functions. organelles Examples: Examples: All multicellular organisms including human Bactria are prokaryotes There are over 1.5 million different organisms identified to date. How to put them in groups? This will be based on differences and similarities of several major properties among living organisms to put them into different groups. Genotype and Phenotype The genotype Is a set of genes in DNA responsible for unique traits or characteristics. The phenotype Is the physical appearance or characteristic of an organism. Basis of Classification of Microorganisms Microorganisms are classified based on: 1- Phenetic characteristics 2- Genotypic 3- Phylogenetic 1- Phenetic characteristics Is the classical approaches to taxonomy that make use of morphological , physiological, ecological, and genetic characteristics. Morphological characteristics  Staining reaction Gram negative & gram positive 2- Genotypic(Molecular Characteristics): This is the most powerful approaches to taxonomy through the study of proteins and nucleic acids which are the direct gene products or the genes themselves, yielding considerable information about true relatedness. The more recent molecular approaches in prokaryotic taxonomy are: 1- Comparison of Proteins 2- Nucleic Acid Base Composition 3- Nucleic Acid Hybridization 4- Nucleic Acid Sequencing 3- Phylogenetic Is the studying of evolutionary distance and evolutionary relationships rather than general resemblance Classification Systems : Phenetic system grouping organisms together based on overall similarity 1- Phylogenetic classification Grouping organisms together based on probable evolutionary relationships rather than general resemblance (the direct comparison of genetic material and gene products such as RNA and proteins solves many of these problems. 2- Molecular or Genetic classification This is based on the degree of genetic relatedness of different organisms. DNA relatedness can be tested by studying the nucleotide sequences of DNA and by hybridization or recombination methods. 3- Adansonian or Numerical classification Is the analysis of various types of taxonomic data by mathematical or computerized methods The process begins with a determination of the presence or absence of selected characters in the group of organisms under study. The data are analyzed using mathematical or computerized method using specific equations to evaluate the similarity coefficient between the organisms