Explain how the phosphate buffer in the media works to maintain a constant pH of 7 throughout the incubation even though S. pyogenes produces acid.
The ingredients in the MR/VP Broth are:
Peptone (protein) 7g
Glucose 5g
Phosphate buffer 5g
Distilled water 1L
Examine the above figure. This figure shows how the pH in the Methyl Red and Voges-Proskauer (MR-VP) broth changes during incubation from time zero to 48 hours with 1) an MR-positive bacteria and 2) a MR-negative bacteria.
We know from the Exercise 5-2 Phenol Red Broth that all of the Unknown Bacteria Species ferment glucose with acid end products. Streptococcus pyogenes is MR negative and VP negative. S. pyogenes does not perform a mixed acid fermentation (purple dashed line). However, S. pyogenes does produce acid from glucose fermentation. Explain how the phosphate buffer in the media works to maintain a constant pH of 7 throughout the incubation even though S. pyogenes produces acid.
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