Bacterial Classification Assoc.Prof.Dr.Yeşim Gürol Free Powerpoint Templates

In this lesson Describe bacterial classification: List taxon levels Define taxonomy and identification Describe principles of taxonomy Explain classification of bacteria

Taxonomy Is the science of classification, especially of living organisms, to facilitate research and communication. Organisms are arranged into taxonomic categories or taxa (singular: taxon), to show degrees of similarities between organisms.

Criteria that drive taxonomy Although genomic analysis has become the final determinant of taxonomy,demonstration of phenotypic features remains the primary means of applying these classifications in diagnostic microbiology.

Based on certain shared genotypic and phenotypic characteristics bacteria are classified into: • Family • Genus • Species • Strain

Genus (plural genera) refers to a group of bacterial organisms that share in common several structural, biochemical and physiological traits Species refers to a subgroup of organisms within a genus that share more specific traits among themselves. The term strain refers to a pure culture made up of descendants of a single isolation

Bacterial classification is based on several major properties Gram staining (and other stains) Morphology Metabolic behavior Infection patterns Intracellular vs extracellular Antigenic composition DNA sequence

Natural classification scheme that reflects major differences in cell wall structure and to some extent the mechanisms involved in disease. Gram positive (blue): single membrane consisting of a thick peptidoglycan layer – no lipopolysaccharide

Gram negative (pink): inner and outer membranes, with outer membrane having lipopolysaccharide molecules

Property discovered by Christian Gram 1883, a Danish botanist, while attempting to differentiate bacteria from human tissue by different staining methods. He noted differences in stain retention by bacteria..

Gram positive cocci in clusters Gram positive cocci in chains

Gram negative cocci Gram negative rods

Morphology Rods or cocci Curved or spiral Filamentous

Metabolic properties may influence ability type of disease caused but not the only factor Aerobe versus anaerobe (microaerophilic, facultative aerobes) Anaerobes have a greater propensity to cause abscesses Brain, lung, liver, intra-abdominal abscesses

Some correlation between morphology and disease Spiral bacteria---Treponemes, Borrelias, Leptospiras, Spirillium tend to cause systemic diseases

Pathogenic filamentous bacteria Actinomyces, Nocardia, Mycobacteria tend to cause chronic diseases Gram positive bacteria, Staphylococcus more likely to cause skin infections, Streptococci skin and pneumonia

The ultrastructure of Escherichia coli (E The ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote                                                                                     

The general size of a prokaryotic cell is about 1-2 um. Note the absence of membrane bound organelles There is no true nucleus with a nuclear membrane The ribosome's are smaller than eukaryotic cells The slime capsule is used as a means of attachment to a surface Only flagellate bacteria have the flagellum Plasmids are very small circular pieces of DNA that maybe transferred from one bacteria to another.

How does an experienced physician approach bacterial diseases? Organ system approach Which bacteria cause disease in a certain location Gram stain approach What does the gram stain show--used to treat empirically before cultures are completed Requires that one is able to get a gram stain which is not always the case

Organ system approach Meningitis Pneumococci, Meningococci, Hemophilus influenzae, Listeria Sinusitis Pneumococci, H. influenzae, Moraxella Acute otitis media Pharyngitis Group A streptococci These are all aerobic bacteria

Now add in the Gram stain Gram negative rods seen in CSF in meningitis H. influenzae Gram positive cocci in meningitis Pneumococcus Gram positive cocci in sinusitis Pneumococcus or Staphylococcus Gram stain may suggest the organism --clusters or diplococci?

Pneumonia Pleural cavity Endocarditis Pneumococcus, Staphylococcus Pneumococcus, H. influenzae Pleural cavity Pneumococcus, Staphylococcus Endocarditis Streptococcus, Staphylococcus, Enterococci

Pneumonia-sputum gram stain Gram positive diplococci as predominant organism Likely organism Pneumococcus--the most common gram positive cocci found in pneumonia Therapy Endocarditis-blood culture positive Gram positive cocci on the stain Maybe Streptococci, Enterococci, or Staphylococci Treatment decision made on this basis- Vancomycin +

Bacteria Archae Eukarya The three phylogenetic lineages of cells (Domains according to comparative rRNA sequences) Bacteria Archae Eukarya

Bacteria :Prokaryotic Archae :Prokaryotic Eukarya :Eucaryotic

Eukaryotic (Greek for true nucleus) Prokaryotic (Greek for primitive nucleus)

Procaryotic cells Bacteria Archae

Bacteria The smallest cells Visible only with the aid of a microscope The smallest bacteria: Mycoplasma,Chlamydia and Rickettsia-0.1-0.2 micrometer Larger bacteria: many microns in length

Most bacterial cells Approximately 1 micrometer in diameter Visible by light microscope Resolution: 0.2 micrometer

Microscopes Light: Electron Bright-field Dark-field (Treponema pallidum-Syphilis_Frengi) Fluorescence Phase contrast (details of the living cell) Electron

Major characteristics of Eucaryotic and prokaryotic cell Eucaryote Prokaryote Size >5 μm 0,5-3 μm Nuclear structure : Nucleus classic membrane no membrane Chromosomes strands of DNA single sircular DNA diploid genome haploid genome

Eucaryote Prokaryote Cytoplasmic Structures Mitokondria + - Golgi bodies + - Endoplasmic reticulum + - Ribosomes 80S(60S+40S) 70S(50S+30S) membrane with sterols no sterol

Differences between Procaryotes Bacteria differ: -morphology (size, shape, stainig characteristics) -metabolic -antigenic and -genetic characteristics

Procaryotic cells Size: micrometer(μm) 10 -6 meter

Size: -the smallest bacteria: Mycoplasma : 0.3 μm Nanobacteria: 0.2-0.05 μm Escherichia coli:2-6 μm Spirochetes: 500 μm red blood cell:7 μm

Capsule:unstained part

Spore:unstained part

Dark-field (Treponema pallidum-Syphilis_Frengi)

Biochemical reactions are used to classify

Sequencing