Thermo Scientific™ M17 Agar (Dehydrated)

Description

• Cultivate lactic streptococci and their bacteriophages and selectively enumerate Streptococcus thermophilus from yogurt with Thermo Scientific™ Oxoid™ M17 Agar (Dehydrated)
• M17 Agar is based on the formulation described by Terzaghi and Sandine 1 and is recommended as an improved medium for the growth and enumeration of lactic streptococci and their bacteriophages
• Lactic streptococci are nutritionally fastidious and require complex media for optimal growth 2,3
• Their homofermentative acid-producing nature require that the medium is well buffered so that the culture pH is maintained above 5.7 during active growth
• This maintenance of the pH is important as lower pH can results in injury and reduced recovery of lactic streptococci
• M17 Agar contains di-sodium glycerophosphate which has sufficient buffering capacity to maintain the pH above 5.7 of actively growing cultures even after 24 hours at 30°C
• This buffering agent also allows the addition of calcium without a precipitation complex being formed
• The calcium-containing medium is used for the assay of bacteriophages of lactic streptococci 1 Shankar and Davies 4 reported that M17 Agar was suitable for the isolation and enumeration of Streptococcus thermophilus from yogurt as the high concentration of di-sodium-glycerophosphate resulted in suppression of Lactobacillus bulgaricus
• M17 Agar has been recommended 5,6 by the International Dairy Federation for the selective enumeration of Streptococcus thermophilus from yogurt
• M17 Agar is also suitable for growing and maintaining starter cultures for cheese and yogurt manufacture as it has little deleterious effect on their subsequent acid-producing ability in milk at either 30°C or 22°C 1
• One further useful property of this agar is its ability to detect streptococcal mutants which are unable to ferment lactose 1
• These mutant Lac- strains form much smaller colonies than the parent lactose fermenting strain
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• Remel™ and Oxoid™ products are now part of the Thermo Scientific brand.