Fighting Bacterial Growth

10 October 2016

Fighting Bacterial Growth The purpose of this lab was to determine the effectiveness of antiseptics, disinfectants, and antibiotics on bacteria. The hypothesis was that if bleach was used, it would be the most effective because bleach is commonly used to clean and disinfect various things. The variables that were tested were antibacterial soap and Scope mouthwash for the antiseptics; bleach and ammonia for the disinfectant; and Cipro, erythromycin, and tetracycline for the antibiotics.

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All of these chemicals were used on the bacteria M. luteus. Two Petri dishes were covered in the bacteria and split into four quadrants, in which each had a disc containing one of the chemicals stated above. One quadrant was left alone with no chemicals for the control group. The dishes were then left for the bacteria to grow, and once obtained again it was obvious that some of the bacteria was killed by the chemicals.

In individual data, there was a zone of inhibition of 3mm in the antibacterial soap; 10mm in the Scope mouthwash; 2mm in the bleach; no zone of inhibition around the ammonia; 10mm in both the erythromycin and the tetracycline, and 15mm for the Cipro. The average length of the halo of inhibition in antiseptics was 8 mm in the E. coli, and 6 mm in the M. luteus. The average length of the halo of inhibition in the disinfectants was 12mm and 11mm respectively. For the antibiotics, it was 7mm and 9mm respectively.

The data represented the hypothesis because for both the E. coli and the M. luteus, the largest zone of inhibition was in the disinfectant; and more specifically, the averages were 28mm in the E. coli and 18mm in the M. luteus in the bleach. In some Petri dishes, the bleach also killed bacteria in the other quadrants, indicating that it killed a lot of bacteria. This also affected some measurements for the other chemicals, because the zone of inhibition for the other chemicals around the bleach could have been caused by the bleach instead of the other chemical.

Another error was that since these Petri dishes were left out for 2 days, there was re-growth in the bacteria in and around the zones of inhibition, like the ammonia in the individual data. In the lab, the chemicals were tested on bacteria to see how much of the bacteria will get killed. What kind of items then would create the most bacterial growth? If bleach was used on different kinds of bacteria, which kinds of bacteria would be most affected by the bleach, and which bacteria will be the least affected by the bleach?

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