B1 Topic 3: Preventing and Treating Disease L/O: To explore how disease is stopped. EBI: Evaluate if the overuse of antibiotics is responsible for superbugs. Great: Explain how antibiotics can be used to treat infection. Good: Explain how antiseptics are used to prevent infection.

An investigator placed paper discs containing different concentrations of an antibiotic onto a culture of bacteria in a Petri dish. After an incubation period of two days, the dish looked like this. (i) Explain why there are areas around some of the paper discs where no bacteria are growing (2)

(iii)    Use the table to describe the effect of an increase in the concentration of the antibiotic on the growth of the bacteria. (2) (iv)     The results of the investigation did not show the best concentration of antibiotic to kill the bacteria. Describe how the experiment could be improved to find the best concentration.

(b) (i) because antibiotics diffuse / pass (into agar) 1 where they kill bacteria (ii)     as a control (iii)    as the concentration increases more bacteria are killed or causes less growth levels off (at 6 units) or the greatest effect is when the concentration is increased from 4 to 6 units (iv)     repeat experiment with more concentrations of antibiotic between 4 and 6 units

“Which antiseptic works best?” Your task “Which antiseptic works best?” Soak the paper discs in different concentrations of acid and place in each quarter. Label your dish. Sellotape the edges. Health and Safety: We are handling e-coli. When handling the dish, do not touch your face or mouth. Do not eat or drink before you have washed your hands. Make sure the equipment used is disinfected, including the tables.

Results Letter Acid Concentration Diameter (Cm) A Control (0) B C D

Antiseptics kill bacteria outside of the body, but are too harsh for use inside the body.

Antibiotics Antibiotics – work inside your body to kill the bacteria that causes diseases. They do this by damaging the cell wall of the bacteria which stops them from taking in too much water and so they eventually explode.

Antifungals Stops fungal infections by either: Damaging the cell walls so the water leaks out and they die OR Preventing the fungus from being able to reproduce

Antibiotic resistance

Why? Many people believe drug resistant bacteria (“superbugs”), such as MRSA, are on the rise due to over-prescription by doctors. Basically: Are doctors giving antibiotics out too easily?

Why?