The purpose of this experiment is to determine if bacteria live on certain US coins, and to determine if the amount of bacteria is related to the coins' surface area. The diameter of a quarter (2.4 cm2), of a dime (1.8 cm2), and of a nickel (2.1 cm2) were measured, and the total surface area of each coin was calculated. To correct for variations in size, 9 quarters, 11 nickels, and 15 dimes were used for each sample. The coins were collected from three sources, soaked for 48 hours in distilled water, then swabbed onto agar plates. After incubating for 48 hours, bacterial colonies were counted, and the number of colonies per cm of each coin were determined.
The study showed that bacteria grows on U.S. coins. There were .2 colonies per cm2 on quarters, .18 colonies per cm2 on nickels, and .45 colonies per cm2 on dimes. Possible explanations for the greater concentration of bacteria on dimes are discussed.