L8 – Keeping things sterile

Learning ObjectiveTo be able to explain the processes used to keep things sterile

Key words: Agar, culture medium,

Starter activity:

B1 L1

For bacterial Infections - Use Antibiotics

For viruses – Don’t use Antibiotics because they do not work against them so it is left alone for the body to deal with.

StarterWhy is it important to use aseptic techniques when growing or dealing with micro-organisms? THINK, PAIR, SHARE

Good

Better

Best

Describe how apparatus is sterilised and how this achieves pure cultures

Explain why you need uncontaminated microorganism cultures to study the effects of different treatments

Success Criteria

At the end of this lesson it will be:

Able to state what aseptic technique is?

How do we grow bacteria and fungi cultures?

• Like all living organism, bacteria and fungi need nutrients, these are supplied using an Agar gel.

• The agar gel is melted and then poured into glass petri dishes and allowed to set.

Agar plates and Petri dishes

The Petri dish is flat to give the microbe plenty of surface to grow on.

How do the Petri dish and incubator provide the best conditions for microbes to grow?

Petri dishes can be kept in incubators

which help the microbes to grow.

The lid stops unknown microbes dropping onto the agar and contaminating the

culture.

Agar is a jelly containing a mixture of nutrients to help the microbe to grow known as a culture medium.

Individual microbes are difficult to see without a microscope. However, if provided with enough FOOD, WARMTH and OXYGEN (although some can live without it), they will rapidly divide to produce a COLONY. This is clearly visible to the naked eye. * We usually grow microbes in special dishes called PETRI DISHES which allow air to pass freely in and out but exclude foreign organisms and their spores.

* We put a jelly-like material called AGAR JELLY in the dishes. The jelly contains food for the microbes.

* All the equipment must be sterilized (heated to a high temperature) to kill any microbes that may already be there.

Colonies and Agar Jelly

Temperature

In school and college laboratories, cultures should be incubated at a maximum temperature of 25 °C,

As pathogens grow much worse at lower temperatures

Keeping the temperature at a maximum of 25 degrees greatly reduces the likelihood of growth of pathogens that might be harmful to humans.

Learning objective check

Good State what is needed to grow bacteria

Collect a handoutAseptic Technique ………………….. cultures of microorganism are required for investigating the action of disinfectants and antibiotics. For this:- Petri dishes and culture media must be ……………… before use to kill unwanted microorganisms - inoculating loops used to transfer ………………… to the media must be sterilised by passing them through a ……….. - the lid of the ………. ………. should be sealed with adhesive tape to prevent microorganisms from the ……… contaminating the culture. In school and college laboratories, cultures should be …………………… at a maximum temperature of …………… which greatly reduces the likelihood of growth of ……………….. that might be harmful to humans. In industrial conditions higher temperatures can produce more ………… growth. Missing words: micro-organisms flame Petri dish pathogens 25°C sterilised uncontaminated air incubated rapid

Why keep things sterile?

What 3 diseases does MMR vaccine protect from?

What is a sterile culture. .

Give 2 reasons it is important to keep cultures sterile. .

What temperature should we incubate cultures at in school and why? How does this compare to industry?.

RULES!Never leave a culture dish open, even for a short time when viewing colonies of organisms, unless you intend to destroy it.

When it is necessary to open a dish, keep the lid close to the dish, open it only as far and as long as is necessary to accomplish the procedure, and keep the lid between your face (and your germs!) and the agar surface.

Before we begin the practical, have you;

•described how to grow micro-organisms safely in your book.

•explained precautions needed when handling microorganisms and growing them safely.

Self Assessment

The task for today.

Growing bacteria in the laboratory

Practical: Growing BacteriaDraw your plate.

You can either follow the instructions on your worksheet, and draw a zig zag on your agar plate, or you can try the streaking method shown in the video.

Remember:

Sellotape lid to the base so it cannot come off

Incubate plate for at least 48 hours

Examine growth of bacteria

The task for today.Practical

Growing Microbes safely in the laboratory.Today you will describe how to grow micro-

organisms safely in your book. You will then carry out a practical to grow micro-organisms found in the classroom. You will draw your plate and label

it carefully.

Growing bacteria in the laboratory

• Harmless bacteria can be grown in the laboratory on agar jelly

• The agar gives the bacteria food and water• The plates containing the agar jelly have to be sterile –

that means ‘germ-free’• The plates are then incubated to make the bacteria

GROW

The task for today.

Aseptic Technique:

CORRECT HANDLING TECHNIQUES

Grasp the culture bottle in one hand; remove the cap with the little finger of the other hand – do not place the cap on the work surface.

Flame the mouth of the bottle for 2 or 3 seconds.

Pass the inoculating loop through the flame until red hot.

Lift the lid of the Petri dish just enough to allow entry of the inoculating loop.

Secure the lid with adhesive tape. Use two pieces to fasten the lid, but do not seal all the way round (this could create anaerobic conditions and encourage the growth of possible pathogenic microbes.

Incubate at around 25oC (cultures should not be cultured at 37oC as this is an ideal temperature for the growth of many pathogenic species.)

Do not open the Petri dish after incubation.

http://www.youtube.com/watch?v=QydH5ZoD_Aw&feature=related