Microbiology:
Q: What three main shapes do bacteria make?
Bacillus or rod-shaped
Coccus or spherical
Spiral or corkscrew shaped.
Q: What causes the shape of bacteria to be different:
The shape of bacteria is due to their rigid cell wall; containing a 3D mesh of
peptidoglycan.
Q: How do you distinguish between gram positive and negative bacteria?
Gram positive: after adding crystal violet and lugols iodine, the peptidoglycan layer
binds to the complex, so stains purple. On treatment with acetone alcohol, the
crystal violet iodine complex is maintained, due to the absence of the
lipopolysaccharide layer. Gram Positive = purple
Gram Negative: after adding crystal violet and lugols iodine, the peptidoglycan layer
binds to the complex, so stains purple. However, on addition of acetone alcohol, the
outer lipopolysaccharide membrane, and the thin inner peptidoglycan layer if left
exposed, this means that the crystal violet/ iodine complex is washed away, losing
the purple colour. They stain red with the counterstain safranin.
Q: What conditions are necessary for culturing bacteria:
1. Nutrients – supplied in nutrient media. Nutrient media supply water, a carbon and
energy source (usually glucose), nitrogen for amino acid syntheisisin the form of
nitrate ions.
2. Growth factors including vitamins such as Na+, Mg2+, Cl-, SO42-, PO43-.
3. Temperature, as bacterial metabolism is maintained by enzymes , the range of 25-45
degrees is suitable for most bacteria.
4. pH – most bacteria are favoured by slightly alkaline conditions (7.4)
5. Oxygen:
Obligate aerobes = require oxygen for metabolism
Obligate aerobes = require no oxygen for metabolism, cannot grow in its presence.
Facultative anaerobes = grow best in oxygen but can survive in its absence.
Q: What does aseptic technique try to prevent?
Contamination of the environment by the microbes being handled.
Contamination of microbial cultures by unwanted microbes from the environment
Q: What three main shapes do bacteria make?
Bacillus or rod-shaped
Coccus or spherical
Spiral or corkscrew shaped.
Q: What causes the shape of bacteria to be different:
The shape of bacteria is due to their rigid cell wall; containing a 3D mesh of
peptidoglycan.
Q: How do you distinguish between gram positive and negative bacteria?
Gram positive: after adding crystal violet and lugols iodine, the peptidoglycan layer
binds to the complex, so stains purple. On treatment with acetone alcohol, the
crystal violet iodine complex is maintained, due to the absence of the
lipopolysaccharide layer. Gram Positive = purple
Gram Negative: after adding crystal violet and lugols iodine, the peptidoglycan layer
binds to the complex, so stains purple. However, on addition of acetone alcohol, the
outer lipopolysaccharide membrane, and the thin inner peptidoglycan layer if left
exposed, this means that the crystal violet/ iodine complex is washed away, losing
the purple colour. They stain red with the counterstain safranin.
Q: What conditions are necessary for culturing bacteria:
1. Nutrients – supplied in nutrient media. Nutrient media supply water, a carbon and
energy source (usually glucose), nitrogen for amino acid syntheisisin the form of
nitrate ions.
2. Growth factors including vitamins such as Na+, Mg2+, Cl-, SO42-, PO43-.
3. Temperature, as bacterial metabolism is maintained by enzymes , the range of 25-45
degrees is suitable for most bacteria.
4. pH – most bacteria are favoured by slightly alkaline conditions (7.4)
5. Oxygen:
Obligate aerobes = require oxygen for metabolism
Obligate aerobes = require no oxygen for metabolism, cannot grow in its presence.
Facultative anaerobes = grow best in oxygen but can survive in its absence.
Q: What does aseptic technique try to prevent?
Contamination of the environment by the microbes being handled.
Contamination of microbial cultures by unwanted microbes from the environment
