title: High temperature in combination with UV irradiation enhances horizontal transfer of stx2 gene from E. coli O157:H7 to non-pathogenic E. coli.
abstract: BACKGROUND
  Shiga toxin (stx) genes have been transferred to numerous bacteria, one of which is E. coli O157:H7. It is a common belief that stx gene is transferred by bacteriophages, because stx genes are located on lambdoid prophages in the E. coli O157:H7 genome. Both E. coli O157:H7 and non-pathogenic E. coli are highly enriched in cattle feedlots. We hypothesized that strong UV radiation in combination with high temperature accelerates stx gene transfer into non-pathogenic E. coli in feedlots.
  
  
  RESULTS
  E. coli O157:H7 EDL933 strain were subjected to different UV irradiation (0 or 0.5 kJ/m(2)) combination with different temperature (22, 28, 30, 32, and 37 °C) treatments, and the activation of lambdoid prophages was analyzed by plaque forming unit while induction of Stx2 prophages was quantified by quantitative real-time PCR. Data showed that lambdoid prophages in E. coli O157:H7, including phages carrying stx2, were activated under UV radiation, a process enhanced by elevated temperature. Consistently, western blotting analysis indicated that the production of Shiga toxin 2 was also dramatically increased by UV irradiation and high temperature. In situ colony hybridization screening indicated that these activated Stx2 prophages were capable of converting laboratory strain of E. coli K12 into new Shiga toxigenic E. coli, which were further confirmed by PCR and ELISA analysis.
  
  
  CONCLUSIONS
  These data implicate that high environmental temperature in combination with UV irradiation accelerates the spread of stx genes through enhancing Stx prophage induction and Stx phage mediated gene transfer. Cattle feedlot sludge are teemed with E. coli O157:H7 and non-pathogenic E. coli, and is frequently exposed to UV radiation via sunlight, which may contribute to the rapid spread of stx gene to non-pathogenic E. coli and diversity of shiga toxin producing E. coli.
authors.affiliation: Department of Animal Science, University of Wyoming, Laramie, Wyoming, United States of America.
authors.forename: Wan-Fu
authors.initials: WF
authors.lastname: Yue
authors.forename: Min
authors.initials: M
authors.lastname: Du
authors.forename: Mei-Jun
authors.initials: MJ
authors.lastname: Zhu
mesh_terms: D004926:Escherichia coli / Q000235:genetics*; D019453:Escherichia coli O157 / Q000235:genetics*; D022761:Gene Transfer, Horizontal / Q000528:radiation effects; D006358:Hot Temperature; D022621:Shiga Toxin / Q000235:genetics; D014466:Ultraviolet Rays
chemical_list: D022621:Shiga Toxin