Protocol

1. Obtain milk and incubate at 45 degrees Celsius for 48 hours.
2. Make Tomato Juice Agar, Tryptic Soy Agar, and sucrose fermentation tubes.
3. Dilute the milk by a factor 10 and 100 with saline.
4. Plate each dilution in duplicate on TJA and TSA.
5. Incubate plates at 45 degrees Celsius for 24 hours.
6. Restreak plates until a pure culture of colonies characteristic of Lactobacillus helveticus is obtained.
7. Perform a Gram Stain with the pure culture.
8. Use a colony from the pure culture to inoculate mannitol, sucrose, lactose, and glucose fermentation tubes.
9. Incubate tubes at 45 degrees Celsius for 24 hours and compare the results to those typical of L helveticus. 
10. Perform catalase test