Isolation of Bacteria For this part of the project, we were each provided with an unknown bacteria. In order to obtain pure cultures of the unknown bacteria we had to use the streak plate technique to isolate separate colonies. We used a nutrient and MacConkey agar plate to begin. We used both agars because the nutrient agar allows us to grow the largest number of different types of microbes, yet not all bacteria can grow because it is rich with beef broth and some yeast extracts. McConkey agar only allows gram negative bacteria to grow while inhibiting gram positive bacteria. This agar also contains a pH indicator which allows us to detect if fermentation occurred. The number I was given for my unknown project was number 23. Yes, my colonies …show more content…
To introduce my experimentation, I began with an Indole production test. This test appeared with a negative result which was an indication that my organism does not produce tryptophanase, which means tryptophan was not hydrolyzed. Next I performed a Methyl Red test which at first was inconclusive because it showed red and yellow coloring, which could indicate a positive or negative result. However I concluded it was a positive result for mixed acid fermentation. I also completed a Vogus-proskauer test which also provided me with inconclusive results, but after intense observation also indicated a positive reading for glucose fermentation into acetoin products. Next, I established a Citrate utilization test to determine whether my bacteria could utilize citrate. This test appeared positive, which indicated citrate fermentation. While using a flow chart guiding my next movies, I came to perform a Decarboxylase test to determine if my bacteria could decarboxylate lysine. After inoculation, this test concluded positive results. This lead me to acknowledge that my bacteria was either Serratia marcescens or Serratia liquefaciens. Some strains of Serratia marcescens are capable of producing a pigment which ranges in color from dark red to pale pink, depending on the age of the colonies. This meant that all I needed to do in order to distinguish my bacteria was to determine the effects of temperature of my microbial growth. This lead me to perform a streak plate which was incubated at body temperature, 25 degrees celsius. After incubation, my organism appeared as a pink pigment, in conclusion, it was presumtively Serratia marcescens. S. marcescens is capable of thriving in many different environments, including water, soil, and the digestive tracts of various animals. S. marcescens is involved in hospital acquired infections, particularly catheter associated