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Transcript
Bacterial Taxonomy Dr. Jyotsna Agarwal Professor, Dept. of Microbiology, King George’s Medical University What is taxonomy • Classification: Orderly arrangement and placement of bacteria based on certain characters ie. Address • Nomenclature: giving Names • Families - related bacteria eg. Enterobacteriaceae • Within a family - numerous genus eg. Escherichia, Klebsiella, Salmonella • A genus contains many species eg. E. coli, E. tarda Species • Taxonomical unit • Based on morpholopgy, biochemical properties & antigenic characters • Nucleotide base ratio constant for a given species (AT : GC) • Genetic homology demonstrated by DNA hybridization > 98% Interspecies Classification • • • • • They are identical, may show some differences due to mutation Biotype - based on biochemical reactions Serotype - based on antigens on bacteria Phage type - susceptibility to particular phage Colicin type - substance secreted by some bacteria Molecular typing: Plasmid profile, DNA sequence • A bacterial population derived from a single bacteria by binary fission is called CLONE • A bacterial population obtained from a particular source is called STRAIN Nomenclature • Casual name / Scientific name: eg. Gonococcus / Neisseriae gonorrhoeae Pneumococcus / Streptococcus pneumoniae • • • • Name could be a character: Staphylococcus aureus Place of discovery: Salmonella london Scientist: Clostridium welchii Disease: Clostridium tetani Bacterial Growth & Metabolism Prokaryotes • Asexual reproduction - binary fission • Generation time or doubling time • Clinical implication? Bacterial Growth Curve 4 phases What is a Bacterial colony? • Colony - visible growth on a culture plate. • Colony Forming Unit- CFU ? Bacterial Nutrition • Autotrophs - photo /chemo • Heterotrophs – Need preformed organic compounds – Includes most pathogenic bacteria • Fastidious heterotrophs Bacterial Metabolism • Help us in identifying bacteria by their end products • Help us in knowing how to inhibit bacteria Energy Generating Process • Sugars formed or obtained - broken down to release energy – Aerobic respiration – Anaerobic respiration – Fermentation • Microbes that use aerobic respiration, detoxify generated waste: Catalase: H2O2 ------- H20 and 02 Superoxide dismutase : oxygen radical ----- H20 and O2 Energy Generating Process • Aerobic respiration: – COMPLETE breakdown of glucose to CO2 & H2O – Final electron receptor O2 – Yield = 38 ATP • Fermentation: – Yield = 2 ATP – Endproducts: Lactic acid/Alcohol – Final electron receptor is organic molecule • Anaerobic respiration: – Yield >2 <38 ATP – Absence of oxygen Factors affecting bacterial growth • Oxygen : Obligate /facultative; aerobes / anaerobes; microaerophilics • Temperature • Ph • Osmotic pressure • CO2 Summary • • • • • Bacterial Taxonomy Bacterial growth curve Fastidious /non fastidious bacteria Obligate/facultative anaerobe Obligate aerobes