Bacteriology Media

MR-VP Medium

(Methyl Red-Voges Proskauer Medium, also known as Buffered Peptone Glucose Broth) is used for the differentiation of bacteria by means of the methyl red and Voges-Proskauer reactions.

Range	Bacteriology Media
Composition	Formula per liter of medium: Buffered peptone 7 gm; Dipotassium phosphate 5 gm; Dextrose 5 gm; pH after sterilization 6.9 + 0.2
Directions	Using a light inoculum, inoculate tubes of MR-VP media with 18- to 24-hour pure cultures. Incubate tubes aerobically at 35 ± 2°C for a minimum of 48 hours but preferably for 5 days. Prepare the methyl red indicator by dissolving 0.1 g of methyl red in 300 mL of 95% ethyl alcohol. Add sufficient purified water to make 500 mL. After the appropriate incubation period, aseptically remove aliquots (1 mL for the VP test) of the medium and conduct the following tests: 1. Methyl Red Test – Add 5 drops of methyl red indicator to an aliquot of the broth. Interpret the color result immediately. 2. Voges-Proskauer Test – Empty the contents (15 drops) from the reagent A dropper and 5 drops from the reagent B dropper into 1 mL of broth culture. Shake well after the addition of each reagent to aerate the sample. 3. Most members of the family Enterobacteriaceae give either a positive MR test or a positive VP test. However, certain organisms such as Hafnia alvei and Proteus mirabilis may give a positive result for both tests. 4. Incubation time for the Methyl Red test cannot be shortened by increasing the dextrose concentration in the medium or by heavily inoculating the broth. 5. Incubate MR-negative tests for more than 48 hours and test again. 6. Read the VP test at 48 hours. Increased incubation may produce acid conditions in the broth that will interfere with reading the results. 7. VP reagents must be added in the order and the amounts specified or a weak-positive or false-negative reaction may occur. A weak-positive reaction may be masked by a copper-like color which may form due to the reaction of KOH and α-naphthol. 8. Read the VP test within 1 hour of adding the reagents. The KOH and α-naphthol may react to form a copper-like color, causing a potential false-positive interpretation. 9. Due to the possible presence of acetoin, diacetyl or related substances in certain raw materials,8 the use of media low in these substances (such as MR-VP media) is recommended for this test.
Storage	BioScien MR-VP Medium tube should be stored on receipt store between 2-8°C. Use before expiry date on the label. Product performance is best if used within stated expiry period.
Appearance	The color of BioScien MR-VP Medium tube is Light amber, clear solution in sterile tubes. If there are any physical changes or signs of deterioration (shrinking, cracking, or discoloration), and contaminations for hydrated media, discard the medium.
Specimen	Pharmaceutical samples, Cosmetic samples
Pack sizes	1 option