BY4 - Microbiology

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  • BY4 - Microbiology
    • Penicillin
      • Fermenter is inoculated with a culture of penicillium notatum which grows under optimum condition in the fermenter
      • Takes about 30 hours for penicillin production to begin
      • Penicillin is secreted by the fungus and accumulates in the medium
      • Delay in production occurs because penicillin is a secondary metabolite
    • Serial Dilutions
      • A method of counting the number of bacteria in a sample
      • Autoclave equipment at 121 degrees for 15-20 minutes
      • Place 9cm3 of distilled water into 3 test tubes
      • 1cm3 of the bacterial sample is mixed in the first test tube
      • 1cm3 of the sample of the first test tube is mixed in the second test tube
      • 1cm3 of the sample of the second test tube is mixed in the third test tube
      • Transfer 1cm3 of each sample onto a sterile nutrient agar plate
        • Repeat this to have 3 plates for each sample
        • Use a sterile spreader to spread the sample around the plate
          • Incubate at 25 degrees for 24 hours
          • Select suitable plates (60-100) colonies with countable colonies and count them
            • Calculate the number of bacteria per cm3 of the original sample using a dilution factor
            • Inaccuracies of population number can occur if colonies are clumped together

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