Antibiotics are an important medicine that can destroy bacterial infections, although they are ineffective against viruses. They are often able to cure once-fatal diseases, such as scarlet fever.


Do you know the difference between viral and bacterial infections? Viruses are non-living agents of disease; they are genetic material (DNA or RNA) inside a protein coat, which inject themselves into normal cells. The viruses then re-direct the cells’ functions, forcing them to reproduce viruses until they explode, scattering new viruses to neighboring cells (where the process starts over again). Although antibiotics are ineffective against viruses, white blood cells can destroy them and vaccines (a weakened form of a virus) can build a body’s defenses against them.

Bacteria, on the other hand, are living organisms. They can reproduce very rapidly, under the right conditions. Pathogenic (disease-causing) bacteria are controlled either by killing them or stopping them from reproducing. There are a variety of ways to provide protection from bacteria’s harmful effects: they can be killed through sterilization or pasteurization, antiseptics or disinfectants, or they can be killed by hotter or colder temperatures than they are used to. That is why our bodies produce fevers to fight off bacterial infections; the elevated temperature kills off the harmful bacteria, which can only survive in a very narrow temperature range.

Antibiotics are another way to kill bacteria that has entered the body, without harming normal cells. Usually they inhibit steps in the building of bacteria cell walls, so that the cell dies and is unable to reproduce.


While most environmental bacteria are not harmful to healthy individuals, once concentrated in colonies, they can be hazardous. To minimize risk, wear disposable gloves while handling bacteria, and thoroughly wash your hands before and after. Never eat or drink during bacteria studies, nor inhale or ingest growing cultures. Work in a draft-free room and reduce airflow as much as possible. Keep petri dishes with cultured mediums closed—preferably taped shut—unless sampling or disinfecting. Even then, remove the petri dish only enough to insert your implement or cover medium with bleach or 70% isopropyl alcohol. When finished experimenting, seal dishes in a plastic bag and dispose. Cover accidental breaks or spills with bleach or alcohol for 10 minutes, then carefully sweep up, seal in a plastic bag, and discard.


If you have two petri dishes and some nutrient agar, you can demonstrate how antibacterial agents (such as antibiotics) work. Follow the instructions on your agar bottle to prepare an agar solution, cover the bottom of both petri dishes with the agar, and then leave the dishes with their lids off in a location at room temperature. Leave the culture dishes exposed for about an hour; you can work on the second part of the experiment while you wait.

Cut small squares of paper (blotter paper works well), label them (i.e. ‘L’ for Lysol, ‘A’ for alcohol, etc.), and soak each in a different household chemical you wish to test for anti-bacterial properties. If you have time, you might also experiment with natural antibacterial agents, such as tea tree oil or red pepper. Wipe off any excess liquid and use tweezers to set each of the squares on a different spot in one of the culture dishes. The second culture dish is your ‘control’. It will show you what an air bacteria culture looks like without any chemical agents.

Replace the lids and store the dishes in a dark place like a closet where they will be undisturbed for a few days. After 3-7 days take both culture dishes and carefully observe the bacteria growth in each dish, leaving the covers on. The bacteria will be visible in small, colored clusters called colonies. Take notes of your observations and make drawings. Some of the questions you might want to answer from your observations are: In the control culture, How much of the dish is covered with bacteria? In the sensitivity square test culture, Have the bacteria covered this dish to the same extent as the control culture? What effect have each of the chemicals had on the bacteria growth? Did a particular chemical kill the bacteria or just inhibit its growth?


For further study, you might want to consider using our antibiotic disc set and bacteria study kit.