Bacteriophages reduce experimental contamination of hard surfaces, tomato, spinach, broccoli, and ground beef by Escherichia coli O157:H7

Abstract

A bacteriophage cocktail (designated ECP-100) containing three Myoviridae phages lytic for Escherichia coli O157:H7 was examined for its ability to reduce experimental contamination of hard surfaces (glass coverslips and gypsum boards), tomato, spinach, broccoli, and ground beef by three virulent strains of the bacterium. The hard surfaces and foods contaminated by a mixture of three E. coli O157:H7 strains were treated with ECP-100 (test samples) or sterile phosphate-buffered saline buffer (control samples), and the efficacy of phage treatment was evaluated by comparing the number of viable E. coli organisms recovered from the test and control samples. Treatments (5 min) with the ECP-100 preparation containing three different concentrations of phages (10(10), 10(9), and 10(8) PFU/ml) resulted in statistically significant reductions (P = <0.05) of 99.99%, 98%, and 94%, respectively, in the number of E. coli O157:H7 organisms recovered from the glass coverslips. Similar treatments resulted in reductions of 100%, 95%, and 85%, respectively, in the number of E. coli O157:H7 organisms recovered from the gypsum board surfaces; the reductions caused by the two most concentrated phage preparations were statistically significant. Treatment with the least concentrated preparation that elicited significantly less contamination of the hard surfaces (i.e., 10(9) PFU/ml) also significantly reduced the number of viable E. coli O157:H7 organisms on the four food samples. The observed reductions ranged from 94% (at 120 +/- 4 h posttreatment of tomato samples) to 100% (at 24 +/- 4 h posttreatment of spinach samples). The data suggest that naturally occurring bacteriophages may be useful for reducing contamination of various hard surfaces, fruits, vegetables, and ground beef by E. coli O157:H7.

FIG. 1.

Electron micrographs of the three phages in ECP-100. Bars = 0.1 μm.

FIG. 2.

Reduction of E. coli contamination of glass coverslips and gypsum boards treated with ECP-100 (based on triplicate samples; bars, standard errors of the means). Nonactive control, PBS-treated matrices; dry control, untreated matrices; neutralizer control, control for the absence of free phages on the Nalgene filters after rinsing with PBS. The 10E10, 10E9, and 10E8 PFU/ml format is used to convey phage concentrations of 10¹⁰, 10⁹, and 10⁸ PFU/ml, respectively.

FIG. 3.

Reduction of E. coli contamination of (A) broccoli, (B) tomato, (C) spinach, and (D) ground beef treated with ECP-100 (based on mean values; phage titers are shown in logarithmic scale). The 1.0E + 7, 1.0E + 6, etc., PFU/g format is used to convey phage concentrations of 10⁷, 10⁶, etc., PFU/g, respectively.