Tryptic Soy Agar Test Lab Report

Unknown #11: Citrobacter freundii

Tryptic Soy Agar Test (TSA): TSA is a basic medium that is most similar to nutrient agar. The agar contains carbon, nitrogen, sodium chloride, and agar. This allows for the growth of a large variety of microorganisms to grow and ferment in the medium.

Mannitol Salt Agar (MSA): MSA is a selective and differential medium that favors the growth of salt loving organisms. It is commonly used to distinguish the different species of Staphylococci. If an organism ferments mannitol, an acid will be produced turning the indicator yellow. This is an indication that Staphylococcus aureus ferments with mannitol. Unknown #11 did not ferment with the mannitol, as the colonies did not show any yellow coloration, thus eliminating the possibility that the unknown organism is a type of Staphylococci.
This particular type of agar only allows for the growth of gram negative rods. In performing this particular test, distinguishing factors between lactose fermenters and non-lactose fermenters can be shown. If the organism applied to the agar produces orange colonies, and if the area around the bacteria turns orange as well, then the organism is a lactose fermenter. If the organism is not a lactose fermenter, the colonies will remain green or produce a blue color on the agar. Unknown #11 grew on the Hektoen enteric agar, giving evidence that the organism is a lactose fermenter. This evidence also suggests that the organism is a gram negative rod, as only gram negative rods can ferment with