Science Project Group:  Mary Langan, Julie Lee, Jim Bacchi

Antimicrobial Effects of Heavy Metals

Introduction:

Heavy metals, such as mercury and silver are used in medicine to inhibit bacterial growth (e.g., the tropical application of mercurichrome, argyrol or silver nitrate to cuts or infections).  In this experiment we examined the effects of certain heavy metals (silver and copper)  on microbial survial and growth.  To make this interesting for students we can make this into a inquiry project using coins.

Hypothesis:

Coins made before 1965 used silver metal and present coins are mostly made of copper and nickel metals.  We predict silver coins will inhibit growth of E. coli  mixed microflora colonies.

Materials:

dimes (pre-1965 coins)
dimes (post-1965 coins)
2  Nickels
3 pennies
70% ethanol
E-coli colonies
nutrient agar

Procedure:

1. Make three nutrient agar plates.
2. Sterize coin using 70% ethanol.
3. Innoculate nutrient plates with E. coli using a spreading technique.
4. Place alcohol sterized coins on the plate.
5. Incubate in room temperature for one week.
 

Results:

Plate 1: pennies and nickles (post 1965-coins)

These coins show stimulation of growth, as seen by the thick white band of E.coli colonies around each coin.
 

Plate 2:  Pre 1965 coins

These coins show inhibition of growth. Two of the three coins show clear band around the coin and the third coin also has a very thin inhibition line around the coin.

Plate 3:   Post 1965 coins

The last control plate shows the white stimulated growth around the coins, which was also consistent with the first plate of post-1965 coins.
 

Conclusion:

Thing that can change next round:

1.  Have all three coins on one plate
2. Have daily observations
3. Test coins from different countries to add multicultural perspective
4. Isolate resistant bacterium