In vitro effects of seaweed extracts on intestinal commensals and pathogens of weaned piglets

While the inclusion of certain seaweed extracts in weaner piglet diets leads to a beneficial gut microbial profile, the mode of action is not known. The aim of this study was to evaluate the prebiotic and antimicrobial potential of Laminaria digitata and Ascophylum nodosum extracts in vitro. Both extracts were two-fold diluted from 2 mg/ml to 0.25 mg/ml. The following strains were used at 106 -107 colonyforming unit(CFU)/ml concentrations: Lactobacillus plantarum, L. reuteri, Bifidobacterium thermophilum, Enterotoxigenic Escherichia coli O149 and Salmonella enterica ser Typhimurium PT12. Each concentration of each extract and controls (0 mg/ml) were incubated for 18 h at 37 °C aerobically or anaerobically (B. thermophilum). Final bacterial concentrations were determined by spread plating. All experiments were carried out with technical replicates on three independent occasions. All data were logarithmically transformed and analysed using the PROC GLM (SAS 9.4). The L. digitata extract increased B. thermophilum 0.7 LogCFU/ml at 0.25 mg/ml (P<0.05) and ≥1 LogCFU/ml from 0.5-2 mg/ml (P<0.05), with no effect on lactobacilli. The A. nodosum extract increased B. thermophilum up to 0.9 LogCFU/ml at all concentrations tested (P<0.05). Additionally, a 0.2 LogCFU/ml increase of L. reuteri and L. plantarum was observed at 2 mg/ml (P<0.05) and 1mg/ml (P<0.05), respectively. Both extracts displayed no antimicrobial activity against ETEC or S. Typhimurium. In conclusion, both extracts exhibited bifidogenic activity in vitro, with an additional slight increase of Lactobacillus spp. for A. nodosum, indicating a prebiotic potential.