title: Fate of E. coli O157:H7, Salmonella spp. and potential surrogate bacteria on apricot fruit, following exposure to UV-C light.
abstract: Some soft fruit, such as tree-ripened apricots, cannot be washed with aqueous sanitizers, due to their innate softness and delicate surfaces. In this study, ultraviolet-C (UV-C) light was investigated for its efficacy in inactivating 4-5 individual strains of Escherichia coli O157:H7 and Salmonella spp. on apricots, in addition to a four-strain composite of Shiga toxin-negative E. coli O157:H7 and a cocktail of three attenuated strains of Salmonella Typhimurium and Salmonella Typhimurium LT2. Also, the survival of E. coli O157:H7 and Salmonella spp. after exposure to 74 and 442 mJ/cm² of UV-C was evaluated during post-UV storage at 2 and 20 °C. The fruit was spot inoculated and the areas (ca. 1.5 cm²) of fruit surface with the inoculated bacteria were exposed to UV-C at 7.4 mW/cm². E. coli O157:H7 and Salmonella spp. populations decreased rapidly (1-2 logs) (P<0.05) with increasing UV-C doses of 0 to 74 mJ/cm². Further increases in UV-C dosage achieved only limited additional reductions in bacterial populations. Shiga toxin-negative bacteria and attenuated S. Typhimurium strains, along with S. Typhimurium LT2, responded similarly to corresponding pathogenic E. coli O157:H7 and Salmonella spp. During storage at 2 or 20 °C, populations of pathogenic E. coli O157:H7 and Salmonella spp. on untreated fruit decreased slowly; however, populations on fruit treated with 442 mJ/cm² decreased rapidly at both temperatures. After 8 days at 20 °C or 21 days at 2 °C, E. coli O157:H7 and Salmonella spp. populations on UV-C treated fruit were at least 2 log CFU/g lower than on non-treated controls. Our results suggest that surface-inoculated bacteria survived poorly following UV-C treatment of apricots.
authors.affiliation: Key Laboratory of Food Nutrition and Safety (Tianjin University of Science & Technology), Ministry of Education, Tianjin 300457, China; U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038, USA.
authors.forename: Juan
authors.initials: J
authors.lastname: Yun
authors.forename: Ruixiang
authors.initials: R
authors.lastname: Yan
authors.forename: Xuetong
authors.initials: X
authors.lastname: Fan
authors.forename: Joshua
authors.initials: J
authors.lastname: Gurtler
authors.forename: John
authors.initials: J
authors.lastname: Phillips
mesh_terms: D001419:Bacteria / Q000528:radiation effects*; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000528:radiation effects; D005511:Food Handling; D005516:Food Microbiology; D005638:Fruit / Q000382:microbiology*; D050296:Microbial Viability / Q000528:radiation effects; D027861:Prunus / Q000382:microbiology*; D012475:Salmonella / Q000528:radiation effects; D013696:Temperature; D014466:Ultraviolet Rays
keywords: Escherichia coli O157:H7; Post-UV storage; Salmonella spp.; Soft fruit; Ultraviolet