Spice oil nanoemulsions: Potential natural inhibitors against pathogenic E. coli and Salmonella spp. from fresh fruits and vegetables

Abstract

There has been a surge in the reports of food borne outbreaks associated with fresh fruits and vegetables. Present study proposes the use of spice oil (essential oil) in the form of nanoemulsions as an alternative for conventional chemicals in controlling the microbial load and preventing outbreaks. Stable cumin (Cuminum cyminum) and pepper (Piper nigrum) oil nanoemulsions were formulated by ultrasonic emulsification and minimum inhibitory concentration was determined by tube dilution method. They showed potent anti-quorum sensing activity with 42.2% and 15.8% inhibition in violacein production by C. violaceum CV026, with cumin and pepper oil respectively. Both cumin and pepper nanoemulsion effectively reduced quorum regulated phenotypes in Escherichia coli and Salmonella enterica like bacterial swimming, swarming and biofilm formation along with reduction in EPS production. Cumin oil nanoemulsion (1:2) inhibited biofilm formation to a maximum of 42.56% and 38.92% in E. coli and S. enterica, respectively. Virulence characteristics including auto-agglutination and crystal violet binding notably reduced with both the nanoemulsions. Results of the study imply the potential use of spice oil nanoemulsions as natural inhibitors against bacterial pathogens in fresh fruits and vegetables by effectively disrupting inter-bacterial communications.