LecTop3: Classification of Bacteria & Diagnostic Methods Flashcards
What are the three levels of classification generally employed to distinguish Eubacteria?
Genus-species-strain
- Genus species makes up binomial nomenclature
- Strain helps distinguish further
What was Carl Linnaeus’ major contribution to biological classification of organisms?
He was the inventor of the Binomial System of Momenclature (TAXONOMY).
-Genus and Species
What are two staining methods important in biotyping bacterial species? Describe each briefly
- Gram Stain: Separates ALMOST ALL bacteria into 2 large groups based on their retention of Crustal violet stain.
- Gram+ bacteria = Thicker Peptidoglycan layer in cell membrane (why dye can’t escape)
- Gram- bacteria = Thinner peptidoglycan layer, but has additional polysaccharide and protein cell wall (increases resistance to antibodies)
- Acid-fast stain: Separates bacteria based on their ability to retain stain after acid wash.
- Acid-fast cells retain initial stain (Red)
- Non Acid-fast cells stain blue with counter-stain.
Most acid-fast bacteria are members of what genus? What is the most important species of that genus to Dentists? Why?
- Most acid-fact bacteria are members of the genus Mycobacterium
- Mycobacterium tuberculosis is the most relevant acid-fast bacteria to dentists because it causes TB and is considered a re-emerging disease and may be encountered in patient carriers.
Describe each of the following bacterial cell shapes (rods & curved rods not included b/c self explanatory):
- Cocci
- Fusiform
- Spirochete
- Square
- Cocci = circular (grape shaped)
- Fusiform = Rods w/ central bulb
- Spirochete = Spiral rod
- Square = Square shaped bacteria that grow in sheets
How effective is colony morphology in defining a specific bacterial species? Give 2 examples to strengthen claim.
Depends upon the bacterial species. Some species, such as S. mutans, grow in multiple colony morphologies dependent upon the external env’t. While other bacterial species, such as Aa, always grow in a specific, defining morphology.
-Note: Aa’s colony morphology always has characteristic stellate shape.
Match the description with the ORAL bacterial species:
- Almost all Gram+ cocci = ?
- Almost all Gram- spirochetes = ?
- Almost all Gram- cocci = ?
- All Gram- bacteria w/ star colony morphology = ?
- All Gram- rods w/ brown-black pigmented colonies = ? and ?
- Streptococcus species
- Treponema species
- Veillonella species
- Aa
- Bacteriodes species and Porphyromonas gingivalis
What is a catalase test? Why is it, and other similar tests, useful?
A catalase test determines whether or not a particular bacteria expresses the enzyme Catalase.
-Enzyme tests are another group of experiments useful for bacterial diagnostics.
What is Biotyping of bacteria based on?
-Give four examples of types of tests used for biotyping.
Biotyping is based on metabolic characteristics of specific biological reactions
- End products of Fermentation rxns
- Acid profiles from sugar fermentations (Ex. Lac+ and Lac- bacteria, pH indicator dye Phenol red is dyed green in the presence of bacteria that can ferment Lactose b/c of acidic byproducts)
- Fatty acid profiles (Gas-liquid chromotagrophy)
- Protein profiles (SDS-PAGE)
What is Serotyping of bacteria based on? Example?
Serotyping is based on immunospecific reactions.
-Such as Antigen-Antibody rxns
What chemical compounds make the best antigens?
Peptides (proteins) & Carbohydrates (sugars)
What are three common types of serotyping assays? What determines which will be used?
- ELISA - Detection of specific antibodies or entire bacteria using antigen-antibody-flourescent antibody reaction
- Immunofluorescence Microscopy - Determine presence of bacteria in solution using antigen-antibody-fluorescent antibody rxn
- Western Blotting - Run out protein products on SDS-PAGE, use antibodies to determine presence of specific antigen proteins in specific bands. Can also transfer to ELISA plate after separation of bands.
- Determination of which serotyping assay will be used depends on specificity required Immunofluorescence Microscopy is really only useful to genome and sometimes species but is also less time consuming and expensive. While western blotting allows you to see what specific bacterial proteins are acting as the antigens.
What is genotyping? What are four methods used? Which doesn’t follow Koch’s postulates?
Genotype: Analytical approach based on DNA sequence analysis.
- 16s rRNA gene sequencing (species identification)
- Polymerase Chain Reaction (PCR) (identify and gene)
- Genomic Sequencing (Slow and expensive but becoming more feasible). Sequence entire bacterial genome, compare to known library. Future of classification.
- Metagenomics. Doesn’t follow Koch’s postulates because don’t isolate individual bacteria and culture in lab but allows you to look at entire microbiota and understand what bacteria are present.
Are all spirochetes gram- or gram+?
All spirochetes are Gram- bacteria.
- How is melanin useful in bacterial classification and diagnostics?
- What is the classic example of a bacterial pigment used in identification?
- It is a pigment produced by certain bacteria.
- In oral cavity Bacteroids species and Porphyromonas gingivalis are gram- rods that produce melanin pigment. - Prodigiosin
