Microorganism: Lab Report

Week 3 of lab, we received our unknown microorganisms. That week we performed a differential staining to determine whether our unknown has a gram-negative envelope which stains red or gram positive envelope which stains blue. Gram-negative microorganisms stain red because of their inability to bind crystal violet and their ability to bind the safranin. Gram-positive microorganism, however, stains blue due to their ability to retain the primary stain, crystal violet. I determined my unknown sample to be a gram-negative microorganism. After viewing the slide under the microscope, I concluded that my unknown gram-negative colony has small microbes that were rod shaped.
The following week, we conducted three tests. Initially, we inoculated an enterotube to determine the identity of our unknown …show more content…
First the SIM test showed that the unknown is motile but is negative for sulfide and indole production. Next, I concluded that my unknown has the ability to reduce nitrate into nitrite using nitrate reductase. Thirdly, the milk agar plate T-streak remained white meaning that the unknown lacks proteases which convert casein into a transparent derivative. The next test determined that my unknown is positive for catalase. Lastly, the oxidase test resulted in a negative reaction. Meaning that my unknown is not an oxidase-producing microbe.
Using Appendix E of the General Microbiology Laboratory lab handbook, I narrowed down the unknown microorganism to Enterobacter aerogenes. Every test matched with my experimental results except for the fermentation of lactose. According to Appendix E, E.aerogenes is able to ferment lactose however my enterotube experiment yielded a negative result. I assume this difference is due to human error of misidentification of the color of the enterotube chamber. Besides, the MacConkey plate yielded a result of red microbial growth meaning that my unknown has the ability to ferment