title: The fate of verocytotoxigenic Escherichia coli C600φ3538(Δvtx2::cat) and its vtx2prophage during grass silage preparation.
abstract: OBJECTIVE
  Silage is grass, preserved by fermentation and used as winter feed for cattle. The impact of a range of current grass silage preparation practices on the survival of Escherichia coli C600φ3538(Δvtx2::cat) and on the induction, release and infectivity of free phage were investigated.
  
  
  RESULTS
  Wilted and fresh grass samples, from plots with and without slurry application, were ensiled with or without formic acid. Each treatment combination was inoculated with approximately 6 log10CFU per g E. coli C600φ3538(Δvtx2::cat) (donor strain) and E. coli C600::kanamycinR(recipient strain) in test-tube model silos and incubated in the dark at 15°C. The physico-chemical (pH, ammonia, ethanol, lactic acid and volatile fatty acids) and microbiological (total viable counts, TVC, total Enterobacteriaceae counts, TEC, E. coli counts, ECC and lactic acid bacteria, LAB) properties of each fermentation were monitored throughout the experiment as were the concentrations of E. coli C600φ3538(Δvtx2::cat), E. coli C600::kanamycinR, free phage and transductants, using culture and PCR-based methods. Over the course of the experiment the pH of the grass samples typically decreased by 2 pH units. TVC, TEC and ECC decreased by up to 2·3, 6·4 and 6·2 log10CFU per g, respectively, while the LAB counts remained relatively stable at 5·2-7·1 log10CFU per g. Both donor and recipient strains decreased by approximately 5 log10CFU per g. Free phages were detected in all treatments and transductants were detected and confirmed by PCR in the silo containing wilted grass, pretreated with slurry and ensiled without formic acid.
  
  
  CONCLUSIONS
  Verocytotoxigenic E. coli may survive the ensiling process and the conditions encountered are sufficient to induce vtx2bacteriophage leading to low levels of phage-mediated vtx2gene transfer.
  
  
  CONCLUSIONS
  These studies suggest that the ensiling of grass may create an environment which facilitates the emergence of new verocytotoxigenic E. coli.
authors.affiliation: Food Safety Department, Food Research Centre, Dublin, Ireland.|School of Veterinary Medicine, University College Dublin, Dublin, Ireland.
authors.forename: S
authors.initials: S
authors.lastname: Nyambe
authors.affiliation: Food Safety Department, Food Research Centre, Dublin, Ireland.
authors.forename: C
authors.initials: C
authors.lastname: Burgess
authors.affiliation: School of Veterinary Medicine, University College Dublin, Dublin, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: Whyte
authors.affiliation: Teagasc Grange Research Centre, Dunsany, Co. Meath, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: O'Kiely
authors.affiliation: Food Safety Department, Food Research Centre, Dublin, Ireland.
authors.forename: D
authors.initials: D
authors.lastname: Bolton
mesh_terms: D000821:Animal Feed / Q000032:analysis / Q000382:microbiology / Q000821:virology; D000818:Animals; D002417:Cattle; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification* / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005285:Fermentation; D005511:Food Handling; D005561:Formates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism; D006109:Poaceae / Q000382:microbiology* / Q000821:virology*; D039002:Prophages / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification* / Q000378:metabolism; D012820:Silage / Q000032:analysis / Q000382:microbiology* / Q000821:virology*
chemical_list: D005232:Fatty Acids, Volatile; D005561:Formates; C030544:formic acid; D019344:Lactic Acid
keywords: emerging pathogens; silage preparation; transduction; verocytotoxigenic Escherichia coli; vtx2 prophage