Survival of a Shiga toxin-encoding bacteriophage in a compost model.
Bacteriophages that carry the Shiga toxin gene (stx) represent an additional hazard in cattle manure-based fertilizers in that their survival could lead to toxigenic conversion of Escherichia coli and other bacteria post-composting. A Stx-phage in which the Shiga toxin (stx(2)) gene was inactivated by insertion of a chloramphenicol resistance gene was used in combination with a rifampicin-resistant E. coli host where RecA is constitutively activated so that all infectious phage particles could be enumerated by plaque assay. PCR-based confirmation methods and the additional application of a host enrichment protocol ensured that very low numbers of surviving bacteriophage could be detected and unequivocally identified. Stx-bacteriophage numbers declined rapidly over the first 48 h and none could be detected after 3 days. The host enrichment method was applied after 6 days and no bacteriophages were recovered. While addition of fresh E. coli cells at intervals after the compost temperature had reduced below 40 degrees C demonstrated that E. coli growth could be supported in the compost, Stx-phages or their lysogens were never detected. Here, we demonstrate that composting animal manure for 40 days during which a temperature of >60 degrees C is maintained for at least 5 days is effective at removing both E. coli and a model infectious Stx-encoding bacteriophage.
Johannessen
Gro S
GS
National Veterinary Institute, P.O.Box 8156 Dep, 0033 Oslo, Norway.
James
Chloe E
CE
Allison
Heather E
HE
Smith
Darren L
DL
Saunders
Jon R
JR
McCarthy
Alan J
AJ
D003090:Coliphages / Q000235:genetics / Q000502:physiology*; D004279:DNA, Viral / Q000032:analysis; D004926:Escherichia coli / Q000821:virology*; D016133:Polymerase Chain Reaction; D039002:Prophages / Q000235:genetics / Q000502:physiology; D022641:Shiga Toxin 2 / Q000235:genetics*; D012987:Soil; D012988:Soil Microbiology; D013696:Temperature; D013997:Time Factors; D010948:Viral Plaque Assay; D038301:Virus Inactivation
D004279:DNA, Viral; D022641:Shiga Toxin 2; D012987:Soil