Antimicrobial activity and antibiotic resistance of Lactobacillus delbrueckii ssp bulgaricus and Streptococcus thermophilus strains isolated from Turkish homemade yoghurts

The aim of this study was to determine the inhibitive effect of 25 Lactobacillus delbruecki ssp. 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. thermophilus strains exhibited the same activity against Klebsiella pneumoniae. None of L. bulgaricus strains 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 to novobiocin, SY72, M3, C1M, and F1M were shown to optochin. ET6 and SY73 strains were found to be resistant in both novobiocin and optochin.