Combined treatment with silver ions and organic acid enhances growth-inhibition of Escherichia coli O157:H7

Individual and combined treatment with silver ions and selected organic acids were evaluated for growth-inhibition of Escherichia coli O157:H7. The concentrations of silver ion were 0.1, 0.3, 0.5, and 1.0 ppm and, citric, lactic, maleic, succinic, and tartaric acids (0.05% and 0.1%) were used. The inhibitory effect was measured during the growth of E. coli O157:H7 in LB broth by optical density at 600 nm. For individual treatments, silver ion at all concentrations and organic acids at 0.1% had a stronger inhibitory effect than untreated control and 0.05% organic acid treatments. For combined treatments, 1.0 ppm of silver ion with 0.1% of organic acids had the greatest inhibitory effect on E. coli O157:H7 growth. With different concentrations, combination with 1.0 ppm of silver ion and 0.05% of organic acids showed greater inhibitory effect than combination with 0.3 ppm of silver ion and 0.1% of organic acids. Combined treatment with silver ion and organic acid showed the enhanced inhibitory effect of E. coli O157:H7 compared to individual treatments. The present study indicated that growth-inhibiting effect of combined treatment was dependant on the concentration of silver ion rather than that of organic acid.