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Levels of Classification

Identifying Bacteria and Viruses
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Methods for Identifying Bacteria
o Morphology
 Better suited for eukaryotes
o Differential staining
 Gram stains
 Acid-fast stains
o Biochemical tests
 Tests for the presence of certain enzymes
o Molecular Genetics Tests
 PCR, rRNA sequencing, RFLP

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Bergey’s Manuals
o Determinate Bacteriology
 Arranged by phenotypes
 Emphasis on identification
o Systematic Bacteriology
 Focused on phylogeny
 More in-depth



Dichotomous Keys
o Flow chart to rapidly eliminate options for microbe identification
o Asks easy yes or no questions
 Example: Is this microbe gram positive?

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Classifying Viruses
o Viruses are acellular
 Requires own classification
o Classified by shape and genetic code
 RNA vs DNA
 Single stranded vs double stranded
 + or – RNA strand
o Grouped into families
 Example: orthomyxovirus
o Grouped into species
 Example: influenza
o Grouped into strains
 Example: influenza A
o Grouped into subtypes
 Example: influenza A H1N1

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Why rRNA?
o Molecular chronometer
o All cells have rRNA genes, they don’t change quickly, and
if they do change, the changes aren’t lethal
Changed phylogenetics
 Study of evolutionary history of organisms
Created 3 domains: bacteria, archaea, and eukarya

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Linnaean System of Classification
o Carol Linnaeus
o Based on similar structures
o Latin names
o Started with 2 kingdoms but expanded to 5 kingdoms
 Animals, plants, fungi, Protoctista, and monera
o Kingdom, phylum, class, order, family, genus, species

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Rules for Scientific Names
o Each name consists of two parts
 Italicized
o Genus is always capitalized while species is not
o The genus can be abbreviated
o Example:
 Escherichia coli (E

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