MRS broth is a medium for the cultivation of lactobacilli and is specifically useful for a number of fastidious strains which is unable to grow properly on other media. MRS broth consists of various nutrients for their proper growth as such carbon, nitrogen, and vitamin sources. Dextrose is present which is fermentable carbohydrate. When an organism is inoculated into the broth medium, those which are capable of fermenting the dextrose survive and utilize other nutrients which is considered as positive result. The turbidity on the medium is the indicator of growth of organism and production of gas during the sugar fermentation is indicated by bubbles seen on the Durham tube in the broth medium. MRS broth is normally used to test the gas production by gram positive Lactic acid bacteria especially, Lactobacillus spp.

Requirements:

• Test tubes
• Incubator
• MRS broth

Composition of MRS broth

Ingredients                                                                     weight (gm/l)

• Dextrose                                                                      20 gm
• Beef extract                                                                10 gm
• Peptic digest of animal tissue                                 10 gm
• Sodium acetate                                                          5.0 gm
• Yeast extract                                                               5.0 gm
• Ammonium citrate                                                   2.0 gm
• Disodium phosphate                                                2.0 gm
• Polysorbate 80                                                           1.0 gm
• Magnesium sulfate                                                   0.1 gm
• Manganese sulfate                                                   0.05 gm

Procedure of MRS test:

• Inoculate MRS broth with an 18 to 24 hour culture of organism .
• Incubate the tube for 24 to 48 hours at 35°-37°C .
• Examine the test tube for turbidity and gas production.

Results interpretation:

• Positive test is indicated by the turbidity of the broth, gas production in the Durham tube in the form of bubbles.
• Negative test is suggested by no turbidity or gas production.

Limitations:

• Organisms other than lactobacilli may grow in this medium, thus appropriate biochemical tests should be performed for confirmation of lactobacilli isolates.
• Some strains may grow poorly or fail to grow at all due to varieties of nutrients in media.
• Biochemical, immunological, molecular or mass spectrometric testing should be performed on colonies from pure culture for complete identification.

MRS Broth test: Principle, Composition, Procedure, and Results interpretation

The post MRS Broth test: Principle, Composition, Procedure, and Results interpretation appeared first on Online Biology Notes.