Describe the six main types of cell shape in bacteria (cell morphology).
- Coccus: round
- Bacillus: rod-shaped
- Vibrio: curved=rod
- Cocobacillus: short-rod
- Sprillium: spiral
6: spirochete
Describe seven types of arrangements.
- Coccus: single coccus
2: Diplococcus: pair of 2 cocci: - Tetrad: grouping of 4 cells in a square
- Streptococcus: chain of cocci
5: Staphylococcus: cluster of cocci
6: Bacillus: single rod - Steptrobacillus: chain of rod
Describe the possible arrangements of flagella.
- Atrocious: no flagella
- Monotrichous: one flagellum at one end
- Lophotrichous: a bunch at one end
- Amphitrichous: flagella at both ends
5: Petrichous: flagella all over the surface - Polar: flagella at one or both poles
Name the six terms that are used to describe the appearance of colonies (colony morphology
- Size (mm)
- Shape
- Pigmentation (colour)
- Margin (edge, entire, undulate)
- Elevation (flat, raised, convex)
- Texture (rough or smooth, shiny or dull)
Describe the relationship between “cell” and “colony”.
Colony = visible mass of bacterial cells that originated from a single bacterial cell
Cell = clones of of the original cell
Describe the structure of peptidoglycan
Repeating units of NAG and NAM linked by glycosidic bonds
Describe the structure of gram-positive and gram-negative cell walls
Gram-Positive:
Thick peptidoglycan
Teichoic acids present
No outer membrane
Stains purple
Gram-negative
Think peptidoglycan
No teichoic acids
Outer membrane (LPS)
Stains pink
Describe the steps of the gram stain procedure (the solutions applied and what they do to the cells).
- Crystal Violet: stains cells purple or blue
- Iodine: cells remain purple or blue
- Alcohol: Gram-positive remains purple, gram-negative cells are colourless
- Safranin: Gram-positive cells remain purple or blue, gram-negative cells appear pink
Which step actually allows differentiation between the two cell types?
Alcohol (decolourization step)
Obligate anaerobe
Requires O2 to grow
Grows only at the top
Facultative Anaerobe
Grows with or without O2
Grows throughout, densest at the the top
Microaerophile
Needs low O2
Growth just below surface
Aerotolerant anaerobe
Doesn’t use O2 but tolerates it
Even growth throughout the tube
Obligate anaerobe
Killed by O2
Growth only at bottom
On what principle are biochemical tests based?
Metabolic and enzymatic properties, allowing for their identification.
Describe a fermentation test.
Determines if bacteria can perform fermentation (breakdown of carbohydrates)
pH indicator = phenol red
Neutral pH – red colour
Acidic pH – yellow colour
An inverted tube = used to detect gas formation (E.g., CO2)
Describe a gelatinase test.
Tests whether an organism can use proteins (i.e presence of extracellular proteases)
Bacterial culture + gelatin
Bacteria grown in gelatin medium then cooled
Liquid after cooling = positive
Solid after cooling = negative
Describe a urease test.
Tests whether an organism can use urea
Bacterial culture + phenol red + urea
positive = magenta
negative = no colour change
Describe an amino acid (or deamination) test.
tests whether an organism can use amino acids
Bacterial culture + phenol red + amino acids
positive = magenta
negative = no colour change
Describe the principle that serology tests are based upon.
antigen-antibody reactions (blood serum)
Positive result: antibody binds to antigen
Negative result: no binding.
Describe a slide agglutination test.
Agglutination – clumping of cells or particles by antibodies Latex beads (particles) can be used either:
to detect specific antibodies (e.g. in patient serum) when coated with antigen
OR
to detect specific antigens (e.g. bacteria) when coated with antibody
Clumping = positive result
.
Serology tests can allow differentiation of bacteria to what taxonomic level?
Strains
Describe a direct and an indirect ELISA test.
Direct ELISA: detects antigen in sample (using known antibody)
Application: drugs or hormones in urine (e.g., home pregnancy test)
Indirect ELISA: detects antibody in sample (using a known antigen)
Application: presence of antibodies in the serum of a patient (e.g test for exposure to a pathogen or need for vaccine booster)
Describe how DNA sequencing is used to identify unknown bacteria.
DNA (or full genome) nucleotide sequence determined
Compared to database of microbial genomes
Most accurate way of determining species
