Microorganisms have been around since the beginning of Earth, but we still have much to learn about them. However, we do know a few things about them. Most people associate bacteria with disease and infection, however only a very small percentage of bacteria can actually act as pathogens. Most bacteria are actually helpful to us as humans. That is why we hear about things like pro-biotics which promote the growth of so called "good" bacteria. A man named Koch developed a few postulates which are now used in modern day science in identifying bacteria and pathogens. We will test Koch's postulates by making yogurt, adding E. coli to some and Ampicillin to some and determining the outcome. We are also practicing how to handle microbes or our microbial technique such as using inoculating loops and agar plates.
We started with 4 tubes filled with milk and then we inoculated one with only yogurt bacteria, one with yogurt bacteria and ampicillin, one with E. coli and leaving only milk in one. We then left the tubes in an incubator overnight to allow the bacteria to grow. We predicted that the yogurt tube would be the only one with actual yogurt in it. We also hypothesized that the tube with yogurt and ampicillin in it would be milk, and that the tube with E. coli in it would be milk. The tube with only yogurt and milk did in fact end up as yogurt, while the tube with the ampicillin-yogurt mixture was more of a combination of yogurt and milk. We correctly hypothesized that the E. coli would end up as milk. The tube with E. coli ended up with a rancid smell, while the two tube with yogurt in them had a yogurt smell, and the milk tube smelled like spoiled milk. We then tested the pH of the tubes with Litmus paper they were all neutral except for the yogurt tube which was between 4 and 5.
The tube with only yogurt ended up as yogurt because it was the only addition to the milk in that tube. The tube with yogurt and ampicillin ended up as a mixture of milk and yogurt because the anti-biotic either didn't have enough time to eliminate all the yogurt bacteria or there was not a large enough amount of it to completely destroy the bacteria that was creating the yogurt. The E. coli tube ended up looking like milk and smelling very spoiled, this is because the bacteria multiplied overnight spoiling the milk. There were a few possible sources of error that could have altered our results, we could have used an inoculating loop that had been contaminated somehow, such as with the bleach that was being used. Another source of error could have been misreading the litmus paper. Also we could have not mixed the mixtures up enough with the vortex.
