Abstract
This project was undertaken as part of a commercial evaluation of two probiotic strains for subsequent use in the European market. Probiotic bacteria are thought to act as competitive exclusion agents against food borne pathogens by several mechanisms. The aim of the study was to characterise the probiotic strains Lactobacillus salivarius 59 and Enterococcus faecium PXN-33, determine the safety of the probiotic strains and to evaluate the strains ability to competitively exclude Salmonella Enteritidis. Analysis of the two novel probiotic strains in vitro confirmed their identity by biochemical and genetic analyses and demonstrated that neither probiotic strains possessed virulence or antibiotic resistance genes. When inoculated into specific pathogen free (SPF) White Leghorn Chicks to test for host tolerance, histological analysis of the gastro intestinal mucosa indicated that L. salivarius 59 and E. faecium PXN-33 were not detrimental towards the host. Inhibition of Salmonella Enteritidis by the probiotic strains was evaluated in vitro using cell free culture supernatant (CFCS) assays and plate diffusion assays. Inhibition was observed in both assays. Priming of macrophages with Enterococcus faecium and subsequent challenge with Salmonella Enteritidis increased TNF-a and IL-6 pro-inflammatory cytokines suggesting Salmonella inhibition was facilitated by immuno-modulation. Following in vitro analysis two in vivo trials were conducted. The first trial involved dosing of SPF chicks by oral gavage with the competitive exclusion (CE) product as individual or dual preparations followed by subsequent inoculation of the birds with Salmonella Enteritidis. A statistically significant reduction of Salmonella Enteritidis as determined by direct microbiological enumeration of samples from GI tissues and cloacal swabs was observed at day 43 in the dual treatment group compared to the control group. In a second study, SPF chicks were dosed with the probiotic preparation using four distinct dosing regimes and challenged by in contact sentinel birds dosed with S. Enteritidis. Significant reductions in Salmonella colonisation were observed in the chicken’s GI tract as compared to control groups.