Comparative Study of Probiotic Cultures to Control the Growth of Escherichia coli O157: H7 and Salmonella typhimurium

Abstract

Pure lactobacilli (Lactobacillus acidophilus, L. plantarum and L. brevis) strains isolated from commercial probiotic consortium (Truferm™) and Bacillus subtilis ATCC 6633 were investigated for their in vitro antagonistic ability against two enteric pathogens (Escherichia coli O157:H7 and Salmonella typhimurium). Generally, both pathogens were inhibited by the probiotic strains but the inhibition of S. typhimurium was greater than that of E. coli. Furthermore, B. subtilis had a better antagonistic activity compared to that recorded for lactobacilli. Among lactobacilli, L. acidophilus exhibited the highest antagonistic activity against both indicator strains. All probiotic strains succeeded to exhibit a positive coaggregation with both faecal pathogens. The maximum coaggregation was reached after 4 h of incubation of indicator strains with lactobacilli and 6 h with B. subtilis. L. acidophilus recorded the highest coaggregation result. Regarding acid and bile tolerance, B. subtilis and L. acidophilus could not survive for 1 h at pH 1.0, whereas, L. plantarum and L. brevis could demonstrate low survival percentages. All strains showed an acid tolerance when incubated at pH 2.0 or 3.0 over a period of 4 h. The highest survival percentage in the acidic conditions occurred with L. acidophilus. B. subtilis recorded the highest bile tolerance over lactobacilli. The sensitivity response of probiotic as well as indicator strains to antibiotics varied.