Influence of Penicillin on the Lactic Acid Production of Certain Lactobacilli

Abstract

The influence of penicillin in skimmilk on the lactic acid-producing ability of Lactobacillus acidophilus, Lactobacillus bulgaricus and Lactobacillus casei was determined. Less than 0.3 unit per milliliter of penicillin in milk did not significantly retard acid development. A decreased amount of lactic acid production by these three species of microorganisms occurred in the range of 0.3 to 0.6 unit of penicillin per milliliter. In concentrations of 2.0 units per milliliter, no acid production was observed in 48 hr. at 35° C. In general, these species of lactobacilli were sensitive to concentrations of penicillin only slightly greater (0.3 to 0.6 unit per milliliter) than the levels that have been previously reported for the lactic acid streptococci (0.1 to 0.4 unit per milliliter) commonly used in dairy starters.