title: Methods for recovering Escherichia coli O157:H7 from cattle fecal, hide, and carcass samples: sensitivity and improvements.
abstract: The Meats Research Unit (MRU) methods, developed by MRU scientists of the U.S. Meat Animal Research Center, have been used to study the prevalence of Escherichia coli O157:H7 in cattle carcass, hide, and fecal samples. The sensitivity of these methods for recovery of injured E. coli O157:H7 cells from inoculated and uninoculated samples was determined, and potential improvements to these methods were evaluated. When using the conventional MRU methods, 91% of the pre-evisceration carcass samples tested positive for E. coli O157:H7 when inoculated with 5 to 10 CFU, 100% of hide samples tested positive for E. coli O157:H7 when inoculated with 30 to 50 CFU, and 96% of the fecal samples produced positive results when inoculated with 300 to 400 CFU per 10 g. The addition of a phosphate buffer to the tryptic soy broth enrichment improved recovery of E. coli O157:H7 from feces. Using the modified enrichment, 92% of the samples were identified as positive when inoculated with 10 to 30 CFU per 10 g. Substituting a commercially available wash buffer for the phosphate-buffered saline (PBS) plus Tween 20 wash buffer during immunomagnetic separation of hide samples improved recovery of the target organism at lower inoculum concentrations. When comparing uninoculated samples, substituting a PBS buffer plus a zwitterionic detergent for PBS plus Tween 20 also had a positive effect on recovery of E. coli O157:H7 from hide samples. Data presented here indicate that the MRU methods are highly effective at recovering injured E. coli O157:H7 from fecal, hide, and beef carcass samples; however, modifications can be added to increase the sensitivity.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska 68933-0166, USA.
authors.forename: Genevieve A
authors.initials: GA
authors.lastname: Barkocy-Gallagher
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Edwards
authors.forename: Xiangwu
authors.initials: X
authors.lastname: Nou
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Bosilevac
authors.forename: Terrance M
authors.initials: TM
authors.lastname: Arthur
authors.forename: Steven D
authors.initials: SD
authors.lastname: Shackelford
authors.forename: Mohammad
authors.initials: M
authors.lastname: Koohmaraie
mesh_terms: D000003:Abattoirs; D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial / Q000379:methods*; D003470:Culture Media; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control; D005516:Food Microbiology; D018189:Immunomagnetic Separation; D012680:Sensitivity and Specificity; D012867:Skin / Q000382:microbiology*
chemical_list: D003470:Culture Media