Antimicrobial activity of selected natural products against Escherichia coli O157:H7 in laboratory medium

Natural antimicrobial products are gaining more attention in the scientific community. The objective of this study was to determine the antimicrobial effect of selected natural products including: copper in combination with lactic acid and essential oils (EO) of armoise and clove bud against E. coli O157:H7. The selected natural products were tested against three strains of E. coli O157:H7 (ATCC 700599, ATCC 43895, and ATCC 51659) in brain heart infusion (BHI) medium using the growth over time assay. Low concentrations of copper ions (10, 20, and 40 ppm) in combination with lactic acids (0.1%, 0.15%, and 0.2% v/v) were tested. EOs were tested at 0.025%, 0.05%, 0.1%, 0.15%, 0.2% and 0.25% (v/v) concentrations. In control samples, E. coli O157:H7 strains continue to grow, turbidity reached 0.933±0.024 optical density (O.D. 610 nm) and bacterial population reached 8.89±0.51 log CFU/mL after 8 h of incubation at 37°C. In the presence of copper (40 ppm) in combination with lactic acid (0.15% v/v), turbidity reached 0.084±0.012 (O.D. 610 nm) and bacterial population reached 4.45±0.72  log CFU/mL after 8 h of incubation at 37°C. EOs of Armoise at 0.15% and clove bud at 0.1% (v/v) concentrations showed bactericidal effect against the tested E. coli O157:H7 strains. At these concentrations, no growth was observed and bacterial populations were below the detectable level (<1 log CFU/mL). These results indicated that combinations of copper and lactic acid or EOs of Armoise or clove bud can be used to control E. coli O157:H7, thereby mitigating food safety concerns.