Abstract

The aim of this study was to determine the inhibitive effect of 25 Lactobacillus delbrueckissp. bulgaricus and 16 Streptococcus thermophilus strains isolated from 30 different homemade yoghurts on several pathogen and contaminant bacteria. The antibiotic resistance of these bacteria was also determined. All of Lactobacillus bulgaricus strains exhibited antimicrobial activity against Escherichia coli, whereas all of S. thermophilusstrains exhibited the same activity against Klebsiella pneumoniae. None of L. bulgaricusstrains were resistant to the polymixin-B, only the OL4 strain has shown resistance to bacitracin. While some strains of S. thermophilus like C6 and SL4 exhibited resistance tonovobiocin, SY72, M3, C1M, and F1M were shown to optochin. ET6 and SY73 strains were found to be resistant in both novobiocin and optochin.

Key words: Antibiotic resistance, antimicrobial activity, homemade yoghurt, lactic acid bacteria, Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus.