Bacterial Growth Over 1 Week

See what sneaky bacteria cover our classrooms

Overview: What is Bacteria?

Bacteria is a cell type that contains very few cell organelles; cytoplasm, cell membrane, ribosomes, (free in cytoplasm) DNA (no nucleus) and flagellum, or flagella as plural. Bacteria cells are thought to have been on Earth some 3.5 billion years ago, among the first primitive organisms (single celled) to touch Earth. Nothing on Earth is really "sterile", or bacteria free. Bacterium can be found everywhere, ranging from your toothbrush, to the bar of soap, to the sidewalk, to icy arctic glaciers, and even your very own body and tissues are covered in bacteria.

Bacteria: How it Grows

Bacteria cells grow in what call "colonies" or groups that are tight together. The reasoning for this is that bacterium grow exponentially, or at an increasingly faster rate. It takes just one bacteria cell to grow a colony very large over night.

What I Tested

We all know that the school is, well, gross. Just think; what do you see walking out of the cafeteria after lunch? Food, scraps, garbage, mushed oranges, white milk spilled- and how often does it get cleaned? Not often- it is far too frequent that the same banana peel from Tuesday is there on Wednesday morning. After noticing this, I decided to test the bacterial growth of the floors over 1 week. I also know that the tables are only cleaned when students are told to by their teachers- again, not very often. I tested the tables too, for one week. Then, I thought about what I predicted to be the most gross location; the doorknobs.


To test the bacterial growth of specific school surfaces over the course of one week, you swab, or gently rub a sterile/clean q-tip on the surface of interest. This is then rubbed on a petri dish that has been prepared with agar which is food for the bacteria. Agar is potato dextrose boiled with water, then poured as a thin layer into the petri dishes. After a couple of hours or overnight depending on the amount of agar in the petri dish, the agar will set or solidify like jello. After the swabbed surface is rubbed on the agar prepared petri dish, the lid is put in place and the dish is set up side down where you are going to keep it for analysis each day of the week. Incubators are a great way to grow bacteria; bacteria thrive in their colonies even more than usual when the environment is warm. After taking these steps, you may see visible growth in just hours.
What Is Bacteria?