Enterobacter Cloacae Experiment

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Antibiotics were initially thought of as a superior drug that could kill many bacterial diseases. Prior to antibiotics, it was hard for anyone to fight a bacteria. However, bacteria are very changing and have begun being able to gain resistance against antibiotics due to overuse, not strong enough dosage of antibiotics, or improper use. By determining the resistance and cross-resistance, one may determine the the relative ability for bacteria to gain resistance to antibiotics. We hypothesis that if we expose Enterobacter cloacae to Tetracycline over a week, then the bacteria will evolve a resistance and the zone of inhibition will decrease. Also, the bacteria will gain a resistance to other antibiotics and biocides, such as Triclosan.
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Zone of inhibition (mean +/- SE) for Enterobacter cloacae after four generations of selection (selected) when exposed to tetracycline and bacteria that was not exposed to antibiotics (control), n=5.

Among the replicates, the zone of inhibition increased initially for replicates B and E but declined after the 2nd generation, whereas the zone of inhibition for replicate A increased at first but declined after the 1st generation (Figure 2). Replicate D had a steady decline for the zone of inhibition over the entirety of the experiment, and the zone of inhibition for replicate C declined at the start, then after the 2nd generation it increased (Figure 2).

Figure 2. Zones of Inhibition (mm) for five replicate samplings of Enterobacter cloacae chosen over three rounds of selective resistance to tetracycline (control).

The selected strain of Enterobacter cloacae which had been exposed to Tetracycline was also exposed to Triclosan on the last day of the experiment. The average zone of inhibition for triclosan on day 8 of selection was slightly smaller (0.8mm +/- 0.8SE). The parent strain of bacteria was also exposed to Triclosan and had a zone of inhibition of (1.4 mm +/- 0.24SE; Figure 3). However this difference in the means was not statistically significant (p=0.55, df=4,
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cloacae gained a cross-resistance to triclosan (Figure 3). The evidence wasn’t very strong as our error bars show that could have been great amount of variability. My t-test (p=0.55, df=4, t=0.65) showed me that we were right that there was a cross-resistance but not a significant difference. We believe that if we lengthened my experiment by a week or two because it would give us a better chance to see the progress the bacteria makes against the antibiotic. Also if we strengthened the concentration of triclosan there would be a significant cross-resistance because it would allow us to see a more accurate

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