Methods Used in Investigation to
Develop Isolation Protocol for S. lactis

 

1. Prepared media from following recipes:

                    Tomato Juice Agar (1)
                           40 ml          Tomato Juice
                           10 g.           Peptonized Milk
                           10 g.           Pancreatic Digest of Casein
                           12 g.           Agar

                           pH ~ 6.1 +/- 0.2 at 25oC

                    i)   Added dH20 to 1 Liter.

                    ii)  Dissolved media components in large flask.

                    iii) Autoclaved media.

                    iv) Poured media in petri dishes and allowed to solidify.
 

                    Tomato Juice Agar (2)
                          100 ml          Tomato Juice
                          100 g.           Skim Milk
                              5 g.           Yeast Extract
                            12 g.           Agar

                   i)   Added skim milk powder to flask then fillled to 500 ml with dH 20.

                   ii)  Added remaining ingredients to a separate flask and filled to 500 ml with                                     dH 2 0.

                   iii) Autoclaved flasks separately.

                   iv) Combined two flasks of media.

                   v)  Poured media in petri dishes and allowed to solidify.


 

2. Isolated S. lactis using enrichment media:

                   i)   Inoculated tomato juice agar (1) and tomato juice agar (2)                                                         plates with fresh whole milk using streak plate technique.

                   ii)   Incubated at 37oC for 48 hours.

                   iii)  Isolated and restreaked colonies with characteristic morphologies on T-Soy 
                        agar.


 

3. Performed confirmatory assays:

                  i) Performed the following procedures for organism identification:
                                   - Gram stain 
                                   - Capsule stain 
                                   - Endospore stain
                                   - Motility stab agar incubated for 48 hours at 37oC
                                   - Oxidase/catalase assay
                                   - Incubation for 48 hours at 37oC in T-Soy Broth
                                   - Incubation for 48 hours at 37oC on MacConkey’s medium
                                   - Incubation for 48 hours at 37oC on sheep's blood agar medium
                                   - Incubation for 48 hours at 37oC in anaerobe chamber
                                   - Carbohydrate Utilization (Glucose and Lactose) 
                                   - 48 hour incubation in adverse temperature conditions 
                                      (4o C and 55 oC) 

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