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Bacterial ClassificationAssoc.Prof.Dr.Yeşim Gürol

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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 cocciin 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. 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

Pneumococci, H. influenzae, Moraxella• Pharyngitis

Group A streptococci

These are all aerobic bacteriaThese 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 • 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 +



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:– 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 DNAdiploid genome haploid genome



Eucaryote Prokaryote• CytoplasmicStructuresMitokondria + -Golgi bodies + -Endoplasmic reticulum + -Ribosomes 80S(60S+40S) 70S(50S+30S)Cytoplasmic 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

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