Plate Inoculation Lab Report

Two different types of procedures were carried out over the course of this experiment: tube inoculation and plate inoculation. We started with plate preparation. Three different lysogeny broth, or LB, agar plates were prepared for E. coli growth every other week: a control where water was used, one for triclosan, and one for streptomycin. Using an inoculation loop, E. coli was transferred from the test tube to the agar plate. This was done to each plate twice, creating a grid-like pattern of bacteria growth. A small paper disk soaked in either water, triclosan, or streptomycin was added to the center of the appropriate plate. To prevent the contamination of bacteria between plates and tubes, the inoculation loop was sterilized using an open flame. The bench all procedures were completed on was also sprayed with bleach before and after plate and tube preparation, to prevent contamination. During the off weeks, when the plate was not prepared, a test tube was prepared to grow our naturally-selected bacteria. After retrieving our plates, we would inoculate the tubes with the most resistant bacteria, selected from the E. coli closest to the zone of inhibition, or ZOI. This was
coli to triclosan, but not to streptomycin. The minimum zone of inhibition diameter decreased by 17.38 millimeters for triclosan, whereas the minimum zone of inhibition diameter for streptomycin increased by 1.44 millimeters. The maximum zone of inhibition diameter for triclosan also decreased by 19.72 millimeters. We saw a fluctuation in the maximum zone of inhibition diameter for streptomycin, increasing by 2.75 millimeters before ultimately decreasing by 1.31 millimeters. As seen in the line graphs Figures 1 and 2, triclosan as a more significant decrease in the size of the zone of inhibition than streptomycin did. The minimum and maximum diameters for each selection round are shown below in Table