Fr

Hugh Leifson medium (M.E.V.A.G)

Bacteria can use carbohydrates through two different metabolic pathways:

A Fermentation pathway in which all reactions may occur in the absence of the oxygen in the air; forms catabolites of especially acid degradation, which accumulate d

An Oxidative pathway in which oxygen air is obligatorily used, and little acidic catabolites are formed. The search for an acidity appeared by oxidation of a carbohydrate must therefore be carried out in a poorly buffered medium, such as medium MEVAG.

☰ The MEVAG medium can be used by two people purposes:

  • - Determination of the Path of Attack of the Glucose,
  • - Study of carbohydrates attacked by oxidative bacteria.
MEVAG

☰ Note: Add sterile 1% glucose prior to inoculation

M.E.V.A.G medium principle


- To study the pathway of attack of a carbohydrate, media containing a only carbohydrate and a pH indicator.

- the presence of glucose as the only carbohydrate and BBT as an indicator of pH. The use of glucose results in an acidification of the medium revealed by the change from bromothymol blue to its acid (yellow) hue.

- the regeneration step which creates a gradient of oxygen.

Seeding technique


  1. Regenerate the tube for 20 minutes at 100°C
  2. Sterilely add the glucose for a final concentration of 1%
  3. Solidify the medium by placing it in a cold water bath
  4. Sow with a central sting using the straight thread.
  5. Incubate for 24 hours at 37°C, cap unscrewed.

Reading and Interpretation M.E.V.A.G


M.E.V.A.G

- Tube 1: little or no culture (no use of glucose) absence acidification: Inert metabolism.

- Tube 2: for the tube with paraffin there is little or no culture and a absence of acidification. In the tube without paraffin, there is moderate acidification, usually the top of the tube is yellow and the rest is green: Oxidative metabolism.

- Tube 3: both tubes are yellow, acidification in both tubes: Fermentative and oxidative metabolism of glucose.

- Tube 4: acidification in the tube with paraffin only: Fermentative metabolism alone.

- Tube 5: the top of the tube is blue, bacteria inert to glucose: use of peptides as an energy source