Simple Anti-microbial ActionTest

In order to test the effectiveness of Silver in a Bottle, 4 Petri dishes are filled with 1 teaspoon of apple sauce each. The 2 dishes on the left have nothing added to them. To each of the 2 dishes on the right, 1/4 teaspoon of Silver in a Bottle is stirred in.

After sitting at room temperature for five days, the 2 untreated samples on the left have spoiled. The 2 treated samples on the right are still completely clear except for 1 spot in the third dish. Could the spot have formed because the silver liquid was not thoroughly mixed?