Investigating how we can kill microbes Lesson Aims: To study how we can kill microbes and to safely set up an experiment to compare different disinfectants.

Lesson outcomes By the end of the lesson you should be able to: use key scientific vocabulary appreciate how to use agar plates to compare disinfectants and achieve reliable results recognise that scientists worked collaboratively to develop the antibiotic penicillin

Use the resources available in the room to find the meaning of the following key vocabulary Antibiotic –. Disinfectant – Antiseptic – a substance that kills micro-organisms and is safe to use on skin. a substance that kills micro-organisms. a substance made by one living thing that kills another living thing.

Comparing disinfectants The purpose of the next 2 lessons is to present evidence in the form of a written report and write a formal letter back to the hospital domestic supervisor (completed in next lesson) summarising your overall findings. SAFETY : You must wear goggles DO NOT open the lid after you have added the filter paper (Dangerous bacteria may grow) Secure the lid with 3 pieces of sticky tape Cover any open skin and wash hands with soapy water before and after the practical Clean your work area

Comparing Disinfectants There has been an outbreak of an infectious bacterial disease at Lincoln Hospital. The domestic supervisor is responsible for ensuring that the correct cleaning methods and procedures are complied with to reduce the spread of the disease. You are a microbiologist who works at the hospital and the domestic supervisor has requested that you test 4 disinfectants to assess which one is the more effective in killing the bacteria causing the disease. The agar jelly in the plates already contains the micro-organism. If left unaffected these can grow

Instructions 1. Using the OHT pen write your initials and date at the outer edge on the bottom dish of the agar plate. Using the china clay pencil divide your agar plate into fifths and label the five areas A, B, C,D and E. Write on the base, not the lid. 2. Areas A, B, C,and D will be treated with the three disinfectant solutions you are testing. 3. To apply the disinfectants to areas A, B, C,D and to apply distilled water to E as a control b) using clean forceps aseptically remove one filter paper disc, saturate it in the solution of disinfectant. c) Remove excess liquid by blotting the wet disc briefly on a paper towel. d) Gently lay the wet disc (in the appropriate position) on the surface of the seeded agar. Take care not to drip chemical on other parts of the plate. Repeat for the different disinfectants and the distilled water. Make sure you record which disinfectant solution was used in each area. 4. Close the agar plate and secure with sticky tape, go over the top and bottom of the plate. Do not go round the edge as air must be able to get in. 6. The plates will be placed in a warm oven, base up, until next lesson. D E C B A

In your exercise book draw a diagram of your agar plate, label each area (A,B,C,D,E) and record which solution you added to each section Make a prediction which disinfectant will be the best and explain why. Read pages Spectrum Biology Answer questions Extension questions 7-10

Lesson outcomes Can you? use key scientific vocabulary appreciate how to use agar plates to compare disinfectants and achieve reliable results recognise that scientists worked collaboratively to develop the antibiotic penicillin