Evolving Superbugs! Omar Kamal and Benny Lo Britannia (Secondary) Floor Location: M120H

Yeast infections are a growing problem in today’s medical community. In this experiment, we investigated yeast and their ability to resist a high concentration of the antifungal nystatin. Yeast develops resistance to low concentrations of nystatin through natural selection. When yeast is treated to a low concentration of nystatin, most yeast cells are killed but a small amount survives. Those that survive are able to resist that concentration of nystatin and require a higher concentration of nystatin to kill.

In the primary experiment, it was investigated if evolved yeast, yeast that had been exposed to gradually increasing concentrations of nystatin for 200 generations, developed resistance to a high concentration of nystatin. The nystatin-treated yeast and ancestral yeast, grown under normal conditions, were both treated to a high concentration of nystatin at the optimal temperature of 30°C. The nystatin-resistance yeast reproduced better than the ancestral yeast while being treated to a high concentration of nystatin. That suggests yeast that has been exposed to increasing concentrations of nystatin for 200 generations evolves resistance to a high concentration of nystatin.

In the temperature experiment, it was investigated if temperature affected the ability of evolved yeast to resist high concentrations of nystatin. Both evolved and ancestral yeast were treated to a high concentration of nystatin at 26°C and 37°C. The growth of the evolved and ancestral at the different temperatures was then compared. While evolved yeast reproduced faster than ancestral yeast at both 26°C and 37°C, there was much overlap in the results with a 95% confidence interval. As a result, it can be suggested that temperature has no significant effect on the ability of yeast to resist a high concentration of nystatin.

In the cross-resistance experiment, it was investigated if yeast that developed resistance to a high concentration of nystatin developed any resistance to other stressors such as a low concentration of ethanol and salt. Evolved yeast was exposed to ethanol and salt. The growth of the evolved yeast in ethanol and salt was compared to the growth of ancestral yeast in ethanol and salt. While the ancestral yeast reproduced faster in the presences of both ethanol and salt, there was much overlap in the results at a 95% confidence interval. Therefore, no definite result can be drawn and it can be suggested that yeast that has developed resistance against a high concentration of nystatin does not develop resistance against a low concentration of ethanol or salt.

These experiments suggested that when yeast is exposed to increasing amounts of nystatin for a long period of time, the yeast will evolve resistance to a high concentration of nystatin. In addition, it was suggested that temperature has no significant effect on the ability of yeast to resist a high concentration of nystatin and that yeast that can resist a high concentration of nystatin cannot resist a low concentration of ethanol or salt.