In vitro screening of synbiotics composed of Lactobacillus paracasei VL8 and various prebiotics and mechanism to inhibits the growth of Salmonella Typhimurium

This study aimed to screen the synbiotics with good antibacterial effect against Salmonella Typhimurium and to investigate its antibacterial mechanism. Laboratory-isolated Lactobacillus paracasei VL8 were selected and combined with four prebiotics, fructooligosaccharide (FOS), inulin, galactooligosaccharide (GOS), and mannan oligosaccharide (MOS) for the comparison. Their growth, adhesion, tolerance and inhibition ability were evaluated by growth curve, non-specific adhesion test, simulated gastrointestinal fluid, and zone of inhibition method, respectively. The results showed that MOS had a better synbiotic effect with L. paracasei VL8, resulting in a significant increase in the growth of L. paracasei VL8, higher acid production, and a larger zone of inhibition of S. Typhimurium, reaching 16.75 mm. The time-kill curves showed that 20% (v/v) of metabolite in the medium could kill S. Typhimurium within 4h completely. Further, electron microscopic micrographs showed that the synbiotic metabolites caused damage to the cell membrane of S. Typhimurium, resulting in cytoplasmic efflux. The Findings indicated that the synbiotic combination between MOS and L. paracasei VL8 not only promoted the growth and acid production of the probiotic, but also exerted good inhibitory effects on S. Typhimurium by disrupting the cell membrane, which can be a potential natural antimicrobial agent for food applications.