Bacterial Identification and Classification

How would you classify humans or a protist (protozoa)

But this system doesn’t work for bacteria

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Methods in bacterial identification1. Microscopic morphology - Gram Staining, Shapes,

arrangements, motility2. Macroscopic morphology – colony appearance, motility3. Physiological / biochemical characteristics – aerobic,

anaerobic, photosynthetic, growth on selective media4. Chemical analysis – e.g.peptides and lipids in cell

membranes5. Phage Typing – which phage infects the bacterium6. Serological analysis – what antibodies are produced against

the bacterium7. Pathogenicity – what diseases does the bacterium cause.8. Genetic & molecular analysis

• G + C base composition• DNA analysis using genetic probes• Nucleic acid sequencing & rRNA analysis

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Methods for identifying bacteria and establish relationships between them

• Pg. 1.23 to 1.24 Lecture notesa. Molecular Approach

1. Via Genomei. DNA Homologyii. DNA hybridizationiii. Biologic hybridizationiv. Nucleotide Sequencing

2. Protein similarity3. Phage Typing4. Serology5. Pathogenicity

b. Diagnostic Approachc. Classification Schemes

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Major Taxonomic Groups of Bacteria per Bergey’s manual

• Mendosicutes – Archaea - primitive prokaryotes with unusual cell walls & nutritional habits

• Eubateria – All true bacteria– Gracilicutes – gram-negative cell walls, thin-skinned

– Firmicutes – gram-positive cell walls, thick skinned

– Tenericutes – lack a cell wall & are soft

For details on classification beyond this point, refer to your Microbiology Lecture Notes

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• species –a collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantly

• strain or variety – a culture derived from a single parent that differs in structure or metabolism from other cultures of that species (biovars, morphovars)

• type – a subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype).

Table 4.7

Table 4.6a

Table 4.6b

Procaryotes with unusual characteristics

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Rickettsias

• very tiny, gram-negative bacteria• most are pathogens that alternate between mammals

and fleas, lice or ticks• obligate intracellular pathogens • cannot survive or multiply outside of a host cell• cannot carry out metabolism on their own • Rickettsia rickettisii – Rocky Mountain spotted fever• Rickettsia prowazekii – epidemic typhus• Coxiella burnetti – Q fever

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Chlamydias

• tiny• obligate intracellular parasites• not transmitted by arthropods• Chlamydia trachomatis – severe eye

infection and one of the most common sexually transmitted diseases

• Chlamydia psittaci – ornithosis, parrot fever• Chlamydia pneumoniae – lung infections

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Mycoplasmas• Smallest free living bacteria• naturally lack a cell wall• stabilized by sterols, resistant to lysis• extremely small• range in shape from filamentous to coccus

or doughnut shaped• Mycoplasma pneumoniae – atypical

pneumonia in humans

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Free-living nonpathogenic bacteria

• Photosynthetic bacteria– Cyanobacteria– Green & purple sulfur bacteria

• Gliding, fruiting bacteria

• Appendaged bacteria– produce an extended process of the cell wall in

form of a bud, stalk or long thread

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Archaea: the other procaryotes• constitute third Domain Archaea• seem more closely related to Domain Eukarya than to

bacteria• contain unique genetic sequences in their rRNA• have unique membrane lipids & cell wall construction• live in the most extreme habitats in nature,

extremophiles• adapted to heat salt acid pH, pressure & atmosphere• includes: methane producers, hyperthermophiles,

extreme halophiles, and sulfur reducers