Last Tuesday, the kids sampled different areas of the house and yard with small swabs and then introduced whatever microbes they captured into Petri dishes. Then we placed the cultures in a bag in an empty room and forgot about them. When an old friend of mine arrived a few days later, the "guest room" smelled like a microbiology lab. Luckily my friend, who himself runs a research lab in Brighton, England, immediately recognized the foul smell of agar and growing beasties. The bacteria were soon transferred outdoors. (Sorry, Claudio!)
A few days of heavy rains followed and the bacteria continued to grow but the humidity caused a lot of fungus to mask the nice colored colonies. But we still grew some cool things. Like this:
As you can see, the bottom half, labelled "clean," has less colonies than the "unclean" half. What's the difference between them? The clean half was not swabbed. The bacteria growing there just happened to land on the agar. On the top half, the kids drew on the agar with a cotton swab full of microbes. What we see above are the colonies that grew from there. The fuzzy spot on the right is a fungus.
In the case of the "control" Petri dish (down below), the kids only opened and closed the dish, without touching the agar. Still lots of colonies grew, from bacteria in the air or our hands or who knows. There are bacteria everywhere!