A patient has the cold, explain to them why antibiotics can only be used to treat certain types of infection and the issues that develop when antibiotics are used too much.

Infections can be caused by bacteria, viruses or fungi. Antibiotics are a class of drug designed to kill or stop the growth of bacteria. They cannot be used to treat infections caused by viruses, such as the common cold, because viruses live inside of host cells. 

Bacteria can become resistant to antibiotics through natural selection. Some bacteria may have mutations that stop them from being affected by an antibiotic. These bacteria are able to survive the antibiotic treatment and can reproduce. This increases the number of bacteria that are resistant to the antibiotic. Infections caused by these bacteria can no longer be treated in the normal way. MRSA  or methicillin-resistant Staphylococcus aureus is an example of a resistant bacteria. It is very hard to treat because it is resistant to lots of antibiotics. If antibiotics are used incorrectly then the chances of resistant bacteria developing increase.