In vitro evaluation of antimicrobial and antioxidant activities of algal extracts

The aim of this study was to evaluate the antioxidant capacity, the antimicrobial proprieties of algae Ascophyllum nodosum and Schizochytrium spp. against one of major swine enteric pathogen Escherichia coli O138 by broth macro-dilution method in Luria–Bertani (LB) medium. The antimicrobial effect of the algal extracts at supplementation of 0.12%, 0.06% and 0.03% (v/v) on E. coli O138, genetically characterised by PCR, was evaluated by following the bacterial growth. The antioxidant activity was determined by the ABTS Radical Cation Decolorisation Assay. In particular, the log₁₀ E. coli used as control resulted significantly higher than 0.12% at 3 hours (8.82 ± 0.07 and 8.18 ± 0.07 log₁₀ cells/mL, respectively; p<.01) suggesting an inhibitory activity related to the dose. No effect activity was observed with Schizochytrium spp. against E. coli growth. A. nodosum and Schizochytrium spp. exhibited antioxidant capacity (p<.05). The combination of them (1:1) exhibited antioxidant activity suggesting a synergistic effect (p<.05). The different proprieties of algal species that can modulate the O138 E. coli growth, one of the major pathogen of swine species, together with the antioxidant capacity, make them a promising functional feed additive to improve the gut health, therefore further studies are needed to confirm these activities in vivo.