Description
Lactic acid bacteria possess bacteriophages requiring complex medium for their assay. Lowrie and Pearce investigated the growth characteristics of these phages and concluded that even very complex formulations may fail to retrieve certain strains of lactic streptococci. They developed a medium know as M16 to overcome this problem, but it did not possess a strong buffering capacity to neutralise the excessive acid production during the growth phase.
It was demonstrated by Terzaghi and Sandine that rapid drops in pH could reduce the number of retrievable organisms and colony size, including that of phage plaques. They varied the M16 formulation to include sodium glycerophosphate, whose strong buffering capacity maintained pH above 5.7 during homo-fermentative utilisation of lactose during the active growth phase at 30°C. This chemical also prevented the formation of precipitate after the addition of calcium when performing phage assays. They called this variant M17, and described a broth to be used in conjunction with it.
