Disk Diffusion Lab Report

Antibiotic Sensitivity of E.Coli and B.Cereus Cora Rebert March 28th 2024 Bio 350-Spring 2024 Collaborated with Emma Mayer and Krystie Webb. I have neither given nor received any unauthorized assistance in the completion of this work. Experiments described here were performed by me and/or my lab partner(s), and this report is entirely my own creative work.

Introduction The purpose of this investigation was to provide a better understanding of the process of a disk diffusion assay and to provide knowledge of how to determine the susceptibility of bacteria to antibiotics. The experiment performed was a disk diffusion assay in which E.Coli and B.Cereus were swabbed onto an agar plate and antibiotics disks were added to the plate to determine

The control disk was removed from the container using the forceps and the petri dish lid was opened. The control disk is placed in the middle of the petri dish, an equal distance from each side of the dish. The petri dish lid was replaced and the forceps were re-sterilized. Penicillin was picked up from the container and placed an equal distance from the control disk and the side of the petri dish. Any antibiotic disks that were dropped were recorded. The steps were repeated for Ampicillin, Tetracycline, Chloramphenicol, and Streptomycin in both petri dishes. Each dish was placed in the incubator and left for 24 to 48 hours. Zones of inhibition were measured in millimeters and recorded after 24 and 48 hours. The zones of inhibition were measured by inverting the petri dish and keeping the lid tight, then measuring the clear diameter. After measuring and recording the zones of inhibition, the susceptibility of the bacteria was found using the Zone Diameter Interpretive Standards for Organisms Other Than Haemophilus and Neisseria gonorrhoeae table. The photographs that were outlined in Figure 1 are visual representations of the

As seen in figure 1 with the pictures of E.Coli in 24 and 48 hrs, there was an increase in diameter for each of the antibiotics except for Penicillin and Tetracycline. The picture of the B.Cereus petri dish after 48 hrs was not taken, however it is shown in the petri dish after 24 hrs that each antibiotic disk formed a zone of inhibition. There was no zone of inhibition around the control disk, meaning the zones of inhibition could be attributed to the antibiotics. The data from Table 2 are the measurements for each sample. Each sample had an increase in diameter except for Penicillin which stayed at 5mm for both bacteria and Tetracycline remaining at 19mm in the B.Cereus sample. All samples except for Penicillin and the B.Cereus sample for Ampicillin were susceptible to the antibiotics based upon the Zone Diameter Interpretive Standards for Organisms Other Than