Antimicrobial Activity of Copper Alone and in Combination with Lactic Acid against Escherichia coli O157:H7 in Laboratory Medium and on the Surface of Lettuce and Tomatoes

Table 1

Growth of E. coli O157:H7 strains in BHI broth (O.D.) after incubation for 8 h at 37°C in the presence of (Cu) and lactic acid (La).

E. coli O157:H7 strains
Treatments	H1730	43895+	43895−	86.24
O.D. 610 nm
Control	0.84^a±0.064	0.81^a±0.014	0.78^a±0.035	0.83^a±0.021
Cu 5 ppm	0.81^ab±0.035	0.78^ab±0.007	0.77^ab±0.021	0.82^ab±0.042
Cu 10 ppm	0.80^ab±0.014	0.76^bc±0.014	0.77^ab±0.007	0.79^bc±0.028
Cu 20 ppm	0.78^b±0.028	0.74^bc±0.014	0.74^ac±0.014	0.75^cd±0.014
Cu 40 ppm	0.76^bc±0.014	0.71^de±0.042	0.65^d±0.007	0.69^ef±0.007
La 0.1%	0.71^cd±0.028	0.69^e±0.021	0.71^c±0.049	0.72^de±0.014
La 0.1% + Cu 5 ppm	0.70^cd±0.014	0.67^ef±0.021	0.71^c±0.021	0.69^ef±0.049
La 0.1% + Cu 10 ppm	0.66^ed±0.007	0.65^f±0.014	0.71^c±0.007	0.69^ef±0.000
La 0.1% + Cu 20 ppm	0.63^ef±0.000	0.61^g±0.021	0.65^d±0.014	0.66^f±0.028
La 0.1% + Cu 40 ppm	0.61^efg±0.028	0.55^h±0.021	0.51^ef±0.021	0.58^g±0.007
La 0.2%	0.58^fg±0.021	0.50^i±0.007	0.54^e±0.007	0.60^g±0.000
La 0.2% + Cu 5 ppm	0.55^g±0.071	0.49^i±0.014	0.48^f±0.021	0.52^h±0.000
La 0.2% + Cu 10 ppm	0.48^h±0.014	0.44^j±0.007	0.38^g±0.007	0.50^h±0.007
La 0.2% + Cu 20 ppm	0.28^i±0.028	0.35^k±0.014	0.28^h±0.007	0.36^i±0.028
La 0.2% + Cu 40 ppm	0.11^j±0.028	0.26^l±0.021	0.17^a±0.007	0.26^j±0.021

Means (± standard deviation) within the same column not followed by the same letters are significantly different (𝑃<0.05).
Initial bacterial population was approximately 3.00 log CFU/mL.