title: Tracking the sources of salmonella in ground beef produced from nonfed cattle.
abstract: The objective of this study was to determine the source(s) of Salmonella contamination in ground beef. One hundred dairy cows were harvested in a U.S. commercial beef processing plant. Samples of hides, carcasses after hide removal and before exposure to antimicrobial intervention,  carcasses after all antimicrobial interventions, superficial cervical lymph nodes from the chuck, trim, ground beef, and air were obtained. Ninety-six percent of the hide samples, 47% of the carcasses before intervention, 18% of the lymph nodes, 7.14% of the trim, and 1.67% of the ground beef  samples were positive for Salmonella. None of the samples obtained from the carcasses after the full complement of interventions and none of the air samples were positive for Salmonella. All Salmonella-positive samples were subjected to pulsed-field gel electrophoresis,  and eight DNA Xba I restriction patterns were identified. The majority of isolates had one of two restriction digest patterns. The strain isolated from ground beef had the same pattern as the strains isolated from hides and from carcasses immediately after hide removal. The Salmonella  isolates from trim samples and lymph nodes also had the same restriction digest pattern. These results indicate that hide and lymph nodes are the most likely sources of Salmonella in ground beef. Dressing practices that effectively reduce or eliminate the transfer of bacteria from hide  to carcass and elimination of lymph nodes as a component of raw ground beef should be considered as measures to reduce Salmonella contamination of ground beef. Because total elimination of lymph nodes from ground beef is not possible, other approaches should be explored. Easily accessible  lymph nodes could be screened for Salmonella very early in the slaughter process. When the results are positive for Salmonella, the corresponding carcasses should be fabricated separately at the end of the production run, and the trim from these carcasses should be subjected  to a treatment that destroys Salmonella.
authors.affiliation: IEH Laboratories and Consulting Group, 15300 Bothell Way N.E., Lake Forest Park, WA 98155, USA. mk@iehinc.com
authors.forename: Mohammad
authors.initials: M
authors.lastname: Koohmaraie
authors.forename: John A
authors.initials: JA
authors.lastname: Scanga
authors.forename: Michael J
authors.initials: MJ
authors.lastname: De La Zerda
authors.forename: Bijan
authors.initials: B
authors.lastname: Koohmaraie
authors.forename: Lourdes
authors.initials: L
authors.lastname: Tapay
authors.forename: Vika
authors.initials: V
authors.lastname: Beskhlebnaya
authors.forename: Tam
authors.initials: T
authors.lastname: Mai
authors.forename: Kay
authors.initials: K
authors.lastname: Greeson
authors.forename: Mansour
authors.initials: M
authors.lastname: Samadpour
mesh_terms: D000818:Animals; D015373:Bacterial Typing Techniques; D002417:Cattle / Q000382:microbiology*; D015169:Colony Count, Microbial; D003612:Dairying / Q000379:methods; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods*; D005525:Food-Processing Industry; D006801:Humans; D008198:Lymph Nodes / Q000382:microbiology; D008461:Meat Products / Q000382:microbiology*; D012475:Salmonella / Q000302:isolation & purification*; D012867:Skin / Q000382:microbiology