Science Buddies: "Ask an Expert"

What would be the easiest way to dilute a bacteria culture in a home setting? The cultures will be taken from random places around a school and the goal is to find the dirtiest place in a school.

I don't exactly know what you mean by diluting a culture in a home setting, however, you can dilute a culture in a petri dish. Once you take your sample, draw 3 intersecting lines - like chords - that touch the ends of the petri dish. The inoculation pattern is such that the culture is diluted so individual colonies can be seen. Here are websites to help you:

http://www.biotopics.co.uk/microbes/tech2.html
http://web.indstate.edu/thcme/micro/basic.html

When you culture the bacteria sample and inoculate it, the first time will contain too much bacteria that individual colonies can't be seen. Taking a sample from the first streak, the second streak will be less diluted, the third even more, and the fourth even more.

Hope this helps,
Sareena