The effect of the pH of various dairy products on the survival and growth of Brucella melitensis.

In this study we report the effect of the pH of various dairy products on the survival and growth of Brucella melitensis. The growth patterns of B. melitensis in broth media at different pHs (ranging between 3 and 9) were studied for up to four weeks, to standardize the growth of the organism at each pH. These growth patterns were compared with those of the same organism growing in different dairy products [milk, soft cheese, yoghurt, and buttermilk (shaneena)] under the same growth conditions. This showed that B. melitensis could survive for more than four weeks in broth at a pH of greater than or equal to 5.5, was inhibited in less than three weeks at pH 5 and in one day at pH 4, but could not survive in a pH of less than 4. In dairy products there was a marked drop in the total viable count, and the organism could not be detected after short periods of time. After 72 hours B. melitensis could be detected only in soft cheese, but it was not detectable in any of the dairy products tested after 96 hours. Thus, this study has shown that the survival of B. melitensis in the different dairy products was inversely proportional to the pH of the product.