Methods

Media

Tomato Juice Agar (TJA)

Tryptic Soy Agar (TSA)

Isolation

Milk was incubated at 45 degrees Celsius in order to spoil it and create an ideal environment for Lactobacillus helveticus.  1 Liter worth of Tomato Juice Agar was prepared.  The spoiled milk was then diluted with saline by a factor of 100, 10,000, and 100,000.  Each dilution was plated on either TSA or TJA.

Number of plates used for each dilution

Plates were incubated at 45 degrees Celsius for 48 hours. 

Confirmation

Those plates not displaying growth typical of Lactobacillus helveticus were discarded.  This typical growth is characterized by small convex colonies, opague in color, and approximately 2-5mm across.  The colonies on the TJA plates with the 10^-2 and 10^-4 dilutions appeared characteristic of L helveticus colonies.  The 10^-6 TSA plate also illustrated such growth.

            Gram Stains were performed on these four plates.  One of the TJA plates with the 10^-2 dilution displayed Gram positive rods and contained only minimal gram negative rods.  Colonies from this plate were restreaked on TJA and incubated for 24 hours at 45 degrees Celsius.  Gram Stains were performed on these samples to confirm the presence of L helveticus. 

Tests 

            100 ml worth of sucrose solution was made in order to create sucrose fermentation tubes. Colonies from the 10^-2 TJA plate were used to inoculate the mannitol, glucose, lactose, and sucrose tubes.  These tubes were incubated for 24 hours at 45 degrees Celsius. A catalase test was also performed.