M17 Agar

M17 Agar contains sodium glycerophosphate which has sufficient buffering capacity to maintain the pH above 5.7. Actively growing cultures of these homofermentative organisms produce large amounts of acid and need a good buffer to maintain the pH above 5.7, thereby guaranteeing the growth conditions of the organisms. This maintenance of the pH is important since a lower pH may cause injury and a reduced recovery of lactic streptococci.

Soy, meat and casein peptones, as well as beef extract, provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is the source of vitamins, particularly of the B-group. Lactose provides the carbohydrate as an energy source. Sodium glycerophosphate increases the buffering capacity of the medium and maintains the pH. Ascorbic acid stimulates the growth of lactic streptococci. Magnesium sulfate provides essential ions for growth. Bacteriological agar is the solidifying agent.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 55 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 45-50 °C, mix well and dispense into plates.

Instructions for use

Inoculate and incubate at 28-30 °C for 48 hours, or up to 2 weeks if required.

• American Public Health Association, Standard Methods for the examination of water and wastewater.
• Terzaghi, B.E., a. Sandine, W.E.: Improved medium for lactic streptococci and their bacteriophages.