Inactivation of Escherichia coli JM109, DH5α, and O157:H7 Suspended in Butterfield's Phosphate Buffer by Gamma Irradiation

Abstract

Food irradiation is a safe and effective method for inactivation of pathogenic bacteria, including Escherichia coli O157:H7, in meat, leafy greens, and complex ready-to-eat foods without affecting food product quality. Determining the radiation dose needed to inactivate E. coli O157:H7 in foods and the validation of new irradiation technologies are often performed through inoculation of model systems or food products with cocktails of the target bacterium, or use of single well-characterized isolates. In this study, the radiation resistance of 4 E. coli strains, 2 DNA repair deficient strains used for cloning and recombinant DNA technology (JM109 and DH5alpha) and 2 strains of serotype O157:H7 (C9490 and ATCC 35150), were determined. The D-10 values for C9490, ATCC 35150, JM109, and DH5alpha stationary phase cells suspended in Butterfield's Phosphate Buffer and irradiated at 4 degrees C were 229 (+/- 9.00), 257 (+/- 7.00), 61.2 (+/- 10.4), and 51.2 (+/- 8.82) Gy, respectively. The results of this study indicate that the extreme radiation sensitivity of JM109 and DH5alpha makes them unsuitable for use as surrogate microorganisms for pathogenic E. coli in the field of food irradiation research. Use of E. coli JM109 and DH5alpha, which carry mutations of the recA and gyrA genes required for efficient DNA repair and replication, is not appropriate for determination of radiation inactivation kinetics and validation of radiation processing equipment.