Lab Exercise 6: The Ubiquity Of Bacteria

Lab Exercise 6: The Ubiquity of Bacteria

Purpose: The purpose of Lab Exercise 6: The Ubiquity of Bacteria is to introduce to the microbiology student, the proper techniques for acquiring bacteria cultures from natural sources and appreciate that bacteria are found everywhere.

Equipment/Tools: 1-test tube of nutrient broth, 1-sterile swab, 1-petri dish with nutrient agar, 1-petri dish with sheep’s blood, 1-incubator, 1-sharpie pen and a cough.

Observations/Results:

One test tube incubated for 120 hours at 98.6 degrees Fahrenheit containing the cultural (macroscopic) characteristics for bacterial cultures grown in nutrient broth revealed moderate growth accompanied by pungent odor, an opaque color, a flocculent surface and a turbid subsurface.

The petri dish was inoculated with a cough and placed in an incubator for 120 hours at 98.6 degrees Fahrenheit. The results from petri dish two revealed minimal growth of bacterial spores. This exercise revealed the desired results.

Answer the following Questions:

1. Why is the level of contamination measured as number of colonies rather than size of colonies?

The number of colonies is related to the amount of bacteria in the original sample, while the size of the colonies is not. Therefore, a single bacterium is invisible to the human eye. However, over time each bacterium will grow and divide, and after 1 or 2 days, colonies will form on the petri dishes. Thus, the number of colonies will tell you the number of bacteria in your original sample, while the size of the colonies should coincide with the amount of time that the plates were left in the incubator.

2. Compare the ribosomes of bacteria (prokaryotic) to the ribosomes eukaryotic microorganisms?

Both prokaryotic and eukaryotic cells have many ribosomes, but the ribosomes found in eukaryotic cells are larger and more sophisticated than those of the prokaryotic