Date of Award

2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Family and Consumer Sciences

First Advisor

Dr. Salam Ibrahim

Abstract

In this study, we modified reinforced clostridial medium (RCM) to selectively enumerate and isolate Lactobacillus bulgaricus, a probiotic and an important starter culture in the dairy industry. The disparity in the reported carbohydrate fermentation pattern of L. bulgaricus was used to develop a growth medium not only selective for L. bulgaricus but significantly inhibitory to the growth of other lactic acid bacteria. A recently modified RCM (mRCM) was optimized for this study by the addition of 0.5% fructose, 0.5% dextrose, 1% maltose and 0.25% sodium pyruvate while replacing lactose as a carbohydrate source. The cell recovery and bacterial counts of L. bulgaricus in tested products (Pure L. bulgaricus strains, Starter Culture, Probiotic Supplements and Yogurt) using our modified RCM with sodium pyruvate (mRCM-PYR) were significantly higher (P < 0.05) than in the recently modified RCM and the common de Man, Rogosa and Sharpe (MRS) culture medium. The growth of other lactic acid bacteria (Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus reuteri) and Bifidobacteria was retarded in this modified medium compared to MRS and mRCM. This result is a significant improvement in the enumeration and differentiation of L. bulgaricus in mRCM-PYR compared to the results in MRS and mRCM where the high background growth of similar species interferes with bacterial population counts. Our results thus suggest that mRCM-PYR could be recommended as an alternative and reliable growth medium for the selective enumeration and isolation of L. bulgaricus in a mixed culture.

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