Microscopic Identification of Bacteria

586 Words2 Pages

The identification of the bacterial unknown was determined through a series of tests using differential media and a gram stain. These tests revealed information about the motility, the metabolism, and the enzymes of the unknown microorganism. The most basic technique for all tests is called the aseptic technique. This technique is “to prevent contamination of the sample” (Leboffe and Pierce, 2010). This is the first technique taught to students in the lab. Aseptic transfers were done with either an inoculating loop or needle between the stock of microorganisms to a sterile media. Sterile media included tryptic soy broth or tryptic soy agar. To prevent contamination, inoculating loops and needles are usually sterilized in the Bunsen burner flame, but in lab, a micro-incinerator was used instead. Other measures taken to avoid contamination include holding an open test tube at an angle and heating the tube’s lip and surrounding air (Leboffe and Pierce, 2010).
A microscopic examination was usually paired with a stain. For example, a Gram stain can be used to identify the shape of the microorganism and the number of peptidoglycan layers it has. The shape can be and type of cell can be used to determine which genera the unknown bacteria could be classified under.
Differential media was used to “distinguish different species of bacteria” (Madigan, Martinko, Stahl, Clark, 2012). While all species of the bacteria are able to survive on the medium, there are visible differences. Selective media was used to promote the growth of specific bacterial species by inhibiting others. Differential and selective media provide more information than a regular media would.
To distinguish a positive result from a negative result for a test, both positive and negative controls are required because results can be varied.
There is no correct species concept for bacteria. The most widely accepted concept groups species “based on overall genomic similarity and sharing of phenotypes deemed ecologically important” (Vos, 2011). This concept is different than the biological species concept used for eukaryotes. The biological species concept defines a species as a group of organisms in a population that is capable of interbreeding and producing viable offspring in nature. Bacteria species do not undergo sexual reproduction making the biological species concept inadequate to define a bacteria species. Another aspect of bacteria that makes it difficult to define a species concept is the ability of prokaryotes to perform horizontal gene transfer.

Open Document