Purpose: The purpose of this study was to evaluate the role of HT and OP on growth promotion of probiotic strains and their antimicrobial effect against growth and virulent gene expression of major foodborne pathogens.
Methods: The minimum bactericidal/inhibitory concentration (MBC/MIC) of HT and OP on enterohemorrhagic Escherichia coli (EHEC) and Salmonella enterica serovar Typhimurium (ST) were determined by broth microdilution method. The effects of HT and OP on Lactobacillus casei, Lactobacillus rhamnosus, and Lactobacillus plantarum or against EHEC and ST were investigated in mixed liquid culture conditions. Several invasion-related virulence genes of ST and EHEC, under stress of HT and OP, were also evaluated by qPCR.
Results: OP, up to 2.0% (w/v), significantly stimulated the growth of all three Lactobacillus strains in a dose-dependent manner, whereas only lower concentrations of HT, up to 0.2%, slightly promoted the growth of L. rhamnosus. In mixed culture condition, 0.05 and 0.2% HT competitively excluded both EHEC and ST within 24 h. Similarly, 1.0 and 2.0% OP completely excluded both EHEC and ST within 24 h. Further, HT significantly (P<0.05) down-regulated the expression of multiple invasion-related virulence genes such as hilA/C/D, invA/C/F/G/H, sipA, and sirA/B for ST and eaeA, espA/B/D, ler, and tir for EHEC (1.5 to 6.0 fold), respectively.
Significance: Both HT and OP could be strong alternative antimicrobials, as well as stimulators for Lactobacillus growth, which may serve as a gut microbiome modulator in preventing foodborne enteric infections.