Agar plate culture grows germs on a jelly-like food inside a flat dish, which lets you count how many live in a sample. This project melts BHI agar into petri dishes and places filters from water bottle samples onto that jelly food. After a day in the incubator, each colony on the dish marks germs that fed and grew on the agar.

Agar plate culture provides a flat dish of jelly-like food that lets germs collected from real surfaces grow into visible colonies you can count. In this project, swabs from restroom door handles transfer any microbes onto blood agar plates, where the jelly food supports bacterial growth during a 48-hour incubation at 35 degrees Celsius. The resulting colonies on each plate become a measurable record of how much bacteria was living on that handle.

Agar plate culture lets you grow germs evenly across a jelly-filled dish so you can see what stops them. This project streaks E. coli onto agar dishes and then exposes each one to a different spice to watch which ones block growth. Because the jelly food feeds the bacteria across the whole surface, any gap in growth shows where a spice killed the germs.

Growing a lawn of E. coli across an agar plate turns the dish into a map you can read. This project collects saliva from 102 dogs using sterile filter paper touched to their upper gums, then places each sample onto that bacterial lawn. Where saliva has antibacterial effects, rings of inhibition appear — zones where the bacteria stopped growing in the jelly food. About 16 percent of samples produced clear inhibition, offering visible evidence of whether dog saliva can kill bacteria.

Agar plate culture turns a flat dish of jelly-like food into a growth surface where germs from a sample spread out and become visible. This project swabs agar dishes with juice from different types of ground beef, so any bacteria in the juice land on the jelly food and begin to feed. After five days of incubation, the amount of the dish covered by bacteria shows how well the germs grew on the agar.