Abstract
One of us 1 found that a small amount of glucose appeared to be essential in media to be used for the cultivation of hemolytic streptococci and pneumococci. It seems likely that by a splitting of this substance to lactic acid, these organisms are able to derive energy for their growth. The amount of growth was roughly proportional to the percent of sugar, up to the point where sufficient acid was produced to check the growth of the organisms. This use of a phosphate buffered broth to delay the culture in reaching a toxic pH, thus allowing the utilization of more glucose and the development of heavier growth, is now very common. However, even a heavily buffered medium will yield not more than 2 or 3 times the volume of bacteria that can be obtained from the ordinary unbuffered infusion broth.
In the preparation of cultures of these organisms for securing large quantities of bacterial sediment or products, one might perhaps, by the occasional addition of sterile NaOH solution, keeping the medium constantly at a pH of 7.2 to 7.8, obtain considerably greater yields than from buffered broth. We have found this to be the case. Ordinary meat infusion broth containing 2% glucose and 5 or 6 drops of 0.2% phenol red solution to 100 cc. is inoculated heavily with a young, plain broth culture of a hemolytic streptococcus or a pneumococcus. After a few hours, when growth commences and the color begins to change from red to yellow, sterile N/1 or stronger NaOH is added from a capillary pipette until the proper red color returns, and incubation is continued. This process is repeated as often as necessary, perhaps every 15 minutes, as long as growth continues.
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