Starter Decide whether the following statements relate to optical methods or dilution plating: Takes a very long time Uses a colorimeter Requires very simple apparatus Need to use a calibration curve Counts only live cells Counts dead and live cells

L2 – Bacterial Growth Understand the different phases of a bacterial growth curve (lag phase, log phase, stationary phase and death phase) and calculate exponential growth rate constants

Independent Study Create a one page revision summary to describe what is meant by aseptic technqiues and how we can measure bacterial growth?

Bacterial Growth media Selective Bacterial Growth Media Broth Cultures Nutrient Agar

Selective growth media For example MacConkey’s Agar (MAC) is used to cultivate Gram-negative bacteria, by discouraging the growth of Gram- positive bacteria through the use of crystal violet dyes and bile salts.

Broth cultures Nutrient broth is typically made of a powdered beef extract. The powder is dissolved in water, put in test tubes, and sterilized.

Nutrient Agar Bacteria cannot digest agar, and the broth-agar contains water, nutrients and often buffers to help regulate pH, all while providing a solid surface for bacteria to grow on. Colony morphology - their characteristic appearance when growing in a group of bacteria that arose from one parent cell.

Questions Describe how to produce a culture of microorganisms: In a flask of broth On a plate of nutrient agar 2. Describe 3 safety precautions that should always be taken when culturing microorganisms and explain their importance. 3. Explain how different media may be used to produce a pure sample of microorganisms for culturing.

Answers Describe how to produce a culture of microorganisms: In a flask of broth – Add water and powdered beef extract, sterilise work surfaces, use a sterilised pipette to add required volume of bacteria to nutrient broth. Make sure neck of bacteria stock is flamed. Incubate and leave to grow. On a plate of nutrient agar – Use sterilised inoculation loop, flame inoculation loop over a Bunsen flame. Flame neck of bacteria stock. Streak loop over pre made agar plate. Seal using tape but not completely.

Answers 2. Describe 3 safety precautions that should always be taken when culturing microorganisms and explain their importance. Do not completely seal up agar plates/petri dishes as this can promote the growth of harmful anaerobic bacteria. Agar plates must be sterilised in an autoclave and bacteria destroyed before disposed of. 3. Explain how different media may be used to produce a pure sample of microorganisms for culturing. Selective growth media Nutrient broth Nutrient agar

Bacterial Population growth curve Spend 5 minutes in your own words describing what you think is happening at stages A-D. H h

What is happening at each stage?

Lag phase Organisms adjusting to their surroundings (taking in water, growing, switching genes on and off, making enzymes) Active cells but not reproducing Numbers do not build up very quickly Length of this phase depends on conditions

Growth Phase http://www.youtube.com/watch?v=gEwzDydciWc

Growth phase Organisms multiply rapidly Size of population doubles every generation (plenty of space and nutrients: not much waste) If bacteria generation is 30 minutes Calculate how many new bacteria an individual can produce in ten hours: Answer: 1,048,576

Stationary Phase Organisms stop reproducing and start to die Lack of food Waste or metabolites build up Births = Deaths In an open system this represents the CARRYING CAPACITY of the environment

Death Phase Deaths outnumber births Food has run out Waste or metabolites at toxic levels In a closed system this would lead to extinction

Exponential Growth rate constant

Complete exam questions

Using the textbooks…

https://www.youtube.com/watch?v=c6pcRR5Uy6w Exponential growth rate

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Answer (c)(i)96 hours ; + 1.5 hours1 (ii)X includes, rapid / exponential / main, growth phase ; ora when primary, metabolites / products are made ; penicillin is a secondary, metabolite / product ; (A) antibiotics (for penicillin) excess of nutrients in X or penicillin produced when nutrients, limited / depleted ;

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