Surrogate organisms for pathogenic O157:H7 and non-O157 Escherichia coli strains for apple juice treatments by UV-C light at three monochromatic wavelengths

Seven non-pathogenic Escherichia coli strains: ATCC 25253, ATCC 25922, ATCC 11775, ATCC 8739, ATCC 11229, NAR and O157 Dm3Na were tested as potential candidates for the surrogate of pathogenic O157:H7 and non-O157 STEC strains (O111:NM, O26:H11, O145:NM and O103:H2) in apple juice treated by UV-C light. The survival studies in apple juice (pH 3.5) revealed that all non-O157 pathogens exhibit acid resistance similar to O157:H7. Subsequently the acid tolerant bacteria, i.e.: all STEC strains, ATCC 11229, ATCC 11775, ATCC 8739 and O157 Dm3Na, were exposed to three UV-C sources emitting light at the wavelengths of 222 nm, 254 nm and 282 nm. The inactivation studies of the nine most UV resistant strains indicated that ATCC 11229 strain can be recommended as a potential surrogate organism for UV treatments of non-O157 STEC strains at 222 nm. In the case of UV-C at 254 nm and 282 nm E. coli ATCC 8739 strain met the criteria for the surrogate organism for O157:H7 and non-O157 STEC strains. The manuscript presents the systematic procedure for the selection and verification of the potential surrogate organisms that can be recommended for validation of UV light processing of high acid juices and beverages.