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Bacteria Classification
By shape: The shape is due to rigid cell wall. Round (coccus) Rod shaped (bacillus)
Spiral shaped (spirillum) Curved rod (vibrio)
By gram staining: Gram negative: The additional lipopolysaccharide layer doesn't allow
the absorption of
crystal violet down to the thin peptidoglycan layer, therefore stains red by counterstain
safranin. Gram positive: The thick peptidoglycan layer is able to retain crystal violet and
safranin but only purple crystal violet stain shows.
By oxygen requirements: Obligate aerobes require oxygen for metabolism.…read more

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Culturing In Laboratories…read more

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Aseptic Technique To prevent contamination into the culture To prevent contamination to
the environment by the culture.
Preventing contamination: Equipment and media are sterilised before use, often by heat.
Autoclave is used at 121°C for 15 minutes. Inoculating loop is sterilised by passing over
Bunsen flame. Plastics which can't be heated are irradiated by gamma rays.
Conditions necessary for culture growth
Temperature: 2545°C, optimum for most enzymes is within this range. 37°C is optimum
for mammalian pathogens. Nutrients: provided in nutrient media (agar).…read more


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