Materials, Methods, and Science Fair Project Help

Maybe you are doing a school science fair project or maybe you just want to test some products yourself. Either way, there is a few more details that you should know about my experiments.

Agar plates

My experiments involve growing bacteria in petri dishes. The petri dishes have a layer of LB-agar growth medium at the bottom and are frequently called "agar plates". LB-agar  is like firm jello and provides food, water, and a nice surface for bacteria, yeast and mold to grow on. I used to make agar plates all the time when I worked in the research lab. However, now I buy them on amazon from Ez BioResearch LLC. It is important to understand that VIRUSES don't grow on these plates. Viruses only multiply inside another cell (like a human cell). None of the experiments that I have done are looking at viruses. Bacteria, yeast, and fungus CAN grow on these plates. When a single LIVE bacterium is placed on an agar plate and put in a warm place (preferably near body temperature, 98.6 degrees F), it will multiply. It will double, and double again, and double again, and double again until you can SEE a small white pile of bacteria called a colony. It usually takes 12-48 hours of incubation at a warm temperature to see the colony. So, when you are looking at these plates of bacteria, look for the number of colonies on the plates and also how big the colonies are to estimate the amount of bacteria. You will also see some wispy white stuff on some plates. That is fungus. Be sure to dispose of the agar plates according to the manufacturers instructions. Wearing gloves and goggles, I pour bleach on them, seal them in a plastic bag, and throw them in the trash. 


I constructed an incubator by attaching a clamp lamp to a plastic box. I put a black reptile heat light bulb in the clamp lamp to produce heat. All through these experiments, the temperature in the incubator was about  90-95 degrees F. I keep a thermometer in the incubator at all times to monitor the temperature. If the incubator gets too hot, your bacteria can die, and give you confusing results. Don't put the stacks of agar plates directly under the light. I put my stacks of agar plates in the corners of the box. 

PRO-TIP=Put the agar plates inside the incubator UPSIDE DOWN. The agar should be on top so the bacteria grow upside down. This is important because lots of condensation will form and fall to the bottom (lid) of the plate. You need to keep the bacteria growing at the top of the plate so they don't get flooded.


All of your experiments need positive and negative controls.
Positive control=something that is definitely going to grow bacteria. A swab of the dogs mouth or dirt is a good positive control because it will definitely grow bacteria. What if the positive control doesn't grow bacteria? That means that either something is wrong with the agar in your plates (maybe they accidentally contain an antibiotic) or maybe the incubator got too hot and killed everything. You need to throw out all your results from that experiment and try again. 

Negative control=something that is not supposed to grow any germs. For a lot of my experiments, I swab tap water and rub it on the plate as my negative control. Usually nothing at all grows. What happens if lots of colonies form on your negative control? That means your plates got contaminated somehow and you have to throw out the results from this experiment and try again. 

FEEL free to contact me if you need help or advice about your science project.--Annie Pryor,