bacterial identification and classification. how would you classify humans or a protist (protozoa)...
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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).
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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
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