Growth inhibition of Escherichia coli by the brown seaweed, Ascophyllum nodosum

Escherichia coli 0157:H7 is an enteric pathogen responsible for more than 21,000 cases of food-related illnesses each year. It is usually transmitted to humans through the consumption of undercooked ground beef Efforts to reduce E. coli populations in cattle through antibiotic supplementation have resulted in the development of antibioticresistant, food-borne pathogens. Previous studies indicate that several species of seaweed have shown antibacterial properties when tested against E. coli strains. Tasco-14 is a seaweed meal made from the drying and grinding of the brown seaweed Ascophyllum nodosum. Supplementation of this product in the diet of beef cattle two weeks prior to slaughter resulted in decreased numbers of E. coli strains, including E. coli 0157:H7. Tasco-EX (seaweed extract) has shown antimicrobial properties against E. coli strains 0157:H7, K-12, and Atir in vitro when tested using standardized methods in both agar and broth media. Tasco-14, supplemented as 2% of the diet, failed to show any antimicrobial properties against E. coli strain EPEC Atir when tested in vitro in an artificial rumen (chemostat). The resulting data indicated a noticeable amount of growth inhibition by Tasco-EX in vitro, whereas results using Tasco-14 were inconclusive. The vitamin and mineral composition of Tasco-14 and Tasco-EX were examined and individual components as well as sub-combinations were screened for antimicrobial activity. Individual metals found in Tasco-14 and Tasco-EX were incapable of inhibiting growth while sub-combinations did display some antimicrobial activity.