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Consumption of produce contaminated with Escherichia coli O157:H7 has resulted in cases of foodborne illness. We determined the efficacy of a mixture of three E. coli O157:H7-specific bacteriophages (ECP-100) in reducing the number of viable E. coli O157:H7 on contaminated fresh-cut iceberg lettuce and cantaloupe. E. coli O157:H7 was spot inoculated on lettuce pieces (9 cm2) with a population of 3.76 log CFU/cm2, allowed to dry, and then sprayed with a control (phosphate-buffered saline) or ECP-100 to deliver 7.98 log PFU/cm2 to lettuce stored for 2 days at 4 degrees C. Cut pieces of cantaloupe were spot inoculated with E. coli O157:H7 (4.55 log CFU/ml) and treated with the control or ECP-100 (6.69 log PFU/ml), and then stored at 4 or 20 degrees C for up to 7 days. On days 0, 2, 5, and 7, cantaloupe samples were homogenized, and populations of E. coli O157:H7 were enumerated. Populations of E. coli O157:H7 on lettuce treated with ECP-100 on 0, 1, and 2 days (0.72, <0.22, and 0.58 log CFU/cm2 of lettuce) and stored at 4 degrees C were significantly (P < 0.05) lower than those treated with the control (2.64, 1.79, and 2.22 log CFU/cm2), respectively. Populations on cut cantaloupes treated with ECP-100 on days 2, 5, and 7 (0.77, 1.28, and 0.96 log CFU/ml) and stored at 4 degrees C were significantly lower than those cut cantaloupes treated with the control (3.34, 3.23, and 4.09 log CFU/ml), respectively. This study is the first to show the effectiveness of bacteriophages to reduce E. coli O157:H7 on fresh-cut lettuce and cantaloupes.

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Aims: To determine the effectiveness of an alkaline cleaner used in food-processing plants and a lytic bacteriophage specific for Escherichia coli O157:H7 in killing wild type and rpoS-deficient cells of the pathogen in a biofilm. Methods and Results: Wild type and rpoS-deficient cells were attached to stainless steel coupons (c. 7-8 log CFU per coupon) on which biofilms were developed during incubation at 22°C for 96 h in M9 minimal salts media (MSM) with one transfer to fresh medium. Coupons were treated with 100 and 25% working concentrations of a commercial alkaline cleaner (pH 11AE9, with 100 lg ml )1 free chlorine) used in the food industry, chlorine solutions (50 and 100 lg ml )1 free chlorine), or sterile deionized water (control) at 4°C for 1 and 3 min. Treatment with 100% alkaline cleaners reduced populations by 5-6 log CFU per coupon, a significant (P £ 0AE05) reduction compared with treatment with water. Initial populations (2AE6 log CFU per coupon) of attached cells of both strains were reduced by 1AE2 log CFU per coupon when treated with bacteriophage KH1 (7AE7 log PFU ml )1 ) for up to 4 days at 4°C. Biofilms containing low populations (2AE7-2AE8 log CFU per coupon) of wild type and rpoS-deficient cells that had developed for 24 h at 22°C were not decreased by more than 1 log CFU per coupon when treated with KH1 (7AE5 log PFU ml )1 ) at 4°C. Conclusions:Higher numbers of cells of E. coli O157:H7 in biofilms are killed by treatment with an alkaline cleaner than with hypochlorite alone, possibly through a synergistic mechanism of alkaline pH and hypochlorite. Populations of cells attached on coupons were reduced by treating with bacteriophage but cells enmeshed in biofilms were protected. Significance and Impact of the Study: The alkaline pH, in combination with hypochlorite, in a commercial cleaner is responsible for killing E. coli O157:H7 in biofilms. Treatment with bacteriophage KH1 reduces populations of cells attached to coupon surfaces but not cells in biofilms.