title: Frozen storage of Escherichia coli O157 in buffered peptone water and its detection on bovine carcasses.
abstract: The adaptation of a standard Escherichia coli O157 isolation method involving immunomagnetic separation and a period of frozen storage was investigated. A series of experiments was designed to test the recovery of a bovine strain of E. coli O157 from buffered peptone water after a period of frozen storage at -80 degrees C. The effects of the addition of glycerol at 5 and 10%, freezing time, the number of freeze-thaw cycles, the method of freezing and the method of thawing, the inclusion of a resuscitation-and-incubation step, and the sensitivity of the isolation method were investigated. The most effective method of storing frozen samples for 6 months and recovering strains of E. coli O157 after storage was found to involve 6 h of incubation of sample material in buffered peptone water at 37 degrees C before frozen storage at -80 degrees C with 10% glycerol, a rapid thaw after frozen storage, and resuscitation at 27 degrees C for 1 h and incubation at 37 degrees C for 1 h to allow freeze-injured and stressed bacteria to recover with a period of growth prior to immunomagnetic separation isolation. There was no significant decrease in log counts of a bovine strain E. coli O157 over 6 months of frozen storage in buffered peptone water with 10% glycerol. With this method, it was possible to isolate E. coli O157 from naturally infected bovine carcasses after a period of frozen storage.
authors.affiliation: Comparative Epidemiology and Informatics, Department of Statistics and Modelling Science, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, UK.
authors.forename: H E
authors.initials: HE
authors.lastname: Ternent
authors.forename: G T
authors.initials: GT
authors.lastname: Innocent
authors.forename: L M
authors.initials: LM
authors.lastname: Filshie
authors.forename: D J
authors.initials: DJ
authors.lastname: Taylor
authors.forename: W B
authors.initials: WB
authors.lastname: Steele
authors.forename: S A
authors.initials: SA
authors.lastname: McEwen
authors.forename: W J
authors.initials: WJ
authors.lastname: Reilly
authors.forename: G J
authors.initials: GJ
authors.lastname: Gunn
authors.forename: S W J
authors.initials: SW
authors.lastname: Reid
authors.forename: D J
authors.initials: DJ
authors.lastname: Mellor
mesh_terms: D000818:Animals; D002417:Cattle / Q000382:microbiology*; D015169:Colony Count, Microbial; D003451:Cryoprotective Agents / Q000494:pharmacology*; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D019453:Escherichia coli O157 / Q000254:growth & development / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D005615:Freezing; D005990:Glycerol / Q000494:pharmacology*; D018189:Immunomagnetic Separation; D008460:Meat / Q000382:microbiology; D013997:Time Factors
chemical_list: D003451:Cryoprotective Agents; D003470:Culture Media; D005990:Glycerol