THE USE OF SELECTED RED MACROALGAE (SEAWEEDS) FOR THE REDUCTION OF SALMONELLA ENTERITIDIS IN POULTRY

Abstract

Red seaweeds are rich in bioactive compounds and secondary metabolites that are known to improve human and animal health. Seaweeds are commercially harvested along Pacific and Atlantic coasts of Canada for a wide range of applications in the pharmaceutical, nutritional, cosmetic, agrichemical and food industries. Salmonella Enteritidis is a zoonotic pathogen which causes infections in humans through contaminated poultry products. Worldwide, Salmonella outbreaks have become an important public health and economic concern. Moreover, the rising concerns for bacterial resistance to antibiotics and increasing consumer concern for drug residues in meat and animal products highlight an urgent need for alternative strategies to antibiotics. To evaluate red seaweeds as a natural alternative to antibiotics against Salmonella Enteritidis infection in poultry, six selected red seaweed species were tested. An in vitro study revealed that two red seaweed species namely Sarcodiotheca gaudichaudii (SG) and Chondrus crispus (CC) exhibited antimicrobial activity against S. Enteritidis. Extracts of both seaweeds reduced biofilm formation and motility of S. Entertitidis. Moreover, lower concentrations of seaweed extracts and compounds isolated from these seaweed species potentiated the activity of an antibiotic (tetracycline). Sub lethal concentrations of tetracycline (MIC25; 4 μg mL-1) in combination with seaweed extracts exhibited antimicrobial activity comparable to full strength tetracycline (25 μg mL-1). Further investigation revealed that seaweed components suppressed the expression of multi-drug efflux pump related genes. The in vivo effect of seaweeds was tested using the Caenorhabditis elegans – S. Enteritidis infection model. Seaweeds reduced bacterial proliferation within the nematode gut and increased the survival of worms which correlated with an up regulation of innate immune response genes in the worm. Since the innate immune response pathways between C. elegans and higher animals are conserved, these results provide evidence that seaweed extract (SWE, CC and SG) may also impart beneficial effects on animal and human health. A poultry trial further revealed that dietary inclusion of the red seaweeds CC and SG in layer feed improved the performance of layers, shifted the gut microbiome towards beneficial bacteria, improved villi height, crypt depth, and elicited an increase in the concentration of Short chain fatty acids (SCFA). This suggests that the cultivated strains of C. crispus and S. gaudichaudii could be used as prebiotics for layer hens. Further, a challenge study showed that seaweed dietary inclusion reduced the negative effect on growth and egg production of S. Enteritidis challenged layer hens. Dietary inclusion of Chondrus crispus (CC) inhibited colonization of S. Enteritidis in the ceca and lowered fecal pathogen shedding. This could be by promoting the growth of Lactobacillus and increasing the concentration of SCFA. To conclude, the results suggested that innovative on-farm strategies such as red seaweed feed supplements can reduce S. Enteritidis colonization in birds. Hence, it can serve as an effective alternative to antibiotics to limit S. Enteritidis associated human infections. Additionally, producers (including organic farmers) would likely accept a natural feed additive like seaweed without concerns for toxicity.