Antagonistic activity of Lactobacillus reuteri strains isolated from different niches against food bacteria and its biopreservative application along with nisin in milk system

Abstract

The objective of the present study was to isolate a potential reuterin producing L. reuteri strain and check its biopreservation efficacy along with nisin in milk system. A total of 35 lactobacilli isolates were obtained from 12 different sources which included faecal samples from infants, adult humans as well as rats and also human milk. Finally, 13 isolates could be confirmed as Lactobacillus reuteri on the basis of PCR. The 13 L. reuteri isolates were then screened for their antimicrobial activity in MRS media with or without glycerol supplementation. It was observed that the supernatant obtained from secondary fermentation from eight L. reuteri isolates in glycerol-supplemented media significantly inhibited the growth of majority of bacterial indicators, which was pH independent. Furthermore the supernatant from the same 8 isolates also exhibited significant antifungal activity against the tested fungal indicators. Based on the RAPD strain profile and reuterin based antimicrobial activity, L. reuteri strain 47 was selected as the most potent isolate for further study. The active units of reuterin in the supernatant of L. reuteri 47 were calculated to be 1600 AU/ml. In the milk system, the reuterin system significantly inhibited E. coli, but not P. acidilactici, nisin on the other hand had significant activity against P. acidilactici but not E. coli. The combination of reuterin and nisin had synergistic effect against L. monocytogenes. Hence, the combination of reuterin and nisin can be utilized to target specific pathogens as well as to improve the overall safety of milk and milk products.