Short Communications Are Super-Shedder Feedlot Cattle Really Super? Krysty D. Munns, 1,2 Lorna Selinger, 1 Kim Stanford, 3 L. Brent Selinger, 2 and Tim A. McAllister 1 Abstract The objective of this study was to determine the frequency and duration of super-shedding in cattle by enumerating Escherichia coli O157:H7 in feces and to compare lineage and pulsed-field gel electrophoresis (PFGE) subtypes from super- and low-shedders. E. coli O157:H7 was enumerated from fecal samples obtained from the rectums of 400 feedlot cattle. Super-shedding steers (N = 11) were identified, transported, and penned individually. Freshly voided fecal pats were sampled 2 h before and 6 h after feeding for 7 d, then once daily for an additional 19 d. Isolates (N = 126) were subtyped using PFGE, and lineage was typed using a lineage-specific polymorphism assay. Of the 11 super-shedders identified at the commercial feedlot, only five were confirmed as super-shedders at the research feedlot, with no super-shedders identified 6 d after sampling at the commercial feedlot. Super-shedding was not consistent in fecal pats collected from the same individual at different times of the day. Isolates exhibited three distinct PFGE subtypes, with most isolates (97.6%) displaying the same subtype, including those obtained from steers that transitioned from super- to low-shedding. The short duration of super-shedding and its lack of continuance suggest that these individuals may not play as great a role in the dissemination of E. coli O157:H7 within the feedlot as previously proposed. Introduction H ealthy cattle transiently host Escherichia coli O157:H7 and directly or indirectly transmit this major foodborne pathogen to humans (Rangel et al., 2005). The load and frequency of E. coli O157:H7 shedding varies greatly among individual cattle (Stanford et al., 2005). Stu- dies typically report shedding of the organism to be sporadic and of short duration, ranging from 10 to 10 7 colony-forming units (CFU)/g feces (Chase-Topping et al., 2008). The term ‘‘super-shedder’’ has been applied to cattle that are high ( > 10 4 CFU/g feces) shedders of E. coli O157:H7 (Matthews et al., 2006a, b). Super-shedders could potentially have a substantial impact on the on-farm prevalence and transmis- sion of E. coli O157:H7 and the risk of adulteration of food products. Matthews et al. (2006b) estimated that super- shedders accounted for 80% of the total E. coli O157:H7 shed into the environment by cattle. The objective of this study was to investigate frequency and duration of super-shedding by cattle. E. coli O157:H7 isolated from super-shedding and low-shedding cattle were genetically characterized using pulsed-field gel electropho- resis (PFGE) and lineage typed to evaluate genetic relation- ships in an attempt to assess the similarity of E. coli O157:H7 from super-shedders and low-shedders. Materials and Methods All cattle were handled according to the Canadian Council of Animal Care (1993). Crossbred yearling feedlot steers (N = 400) from a commercial feedlot in southern Alberta were sampled in July 2011 to identify super-shedders. Cattle from 4 pens were restrained in a chute and a fecal grab sample (50 g) was collected from the rectum. All fecal samples were collected in sterile tubes, placed on ice, and transported to the laboratory for analysis within 4 h. Eleven super-shedders (shedding ‡ 10 4 CFU/g feces) were identified and transported (35 km) to the Lethbridge Research Centre (LRC) after enumeration was complete (4 days). Super-shedders were then housed individually at the LRC feedlot. The 34-d study involved a 7-d sampling period where steers were sampled twice daily by collecting freshly voided fecal pats 2 h before and 6 h after feeding, with sampling continuing daily for an additional 19 d. Five of the 11 steers, exhibiting the highest shedding levels, were shipped for slaughter for detailed analysis of intestinal populations and collection of tissues throughout the digestive tract. E. coli O157:H7 was enumerated and confirmed from fe- cal subsamples (50 g) according to Hallewell et al. (2012). When E. coli was not detectable by plating, duplicate 1-g subsamples of feces were enriched and subjected to im- munomagnetic separation. 1 Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, Alberta, Canada. 2 Department of Biological Sciences, University of Lethbridge, Lethbridge, Alberta, Canada. 3 Alberta Agriculture and Rural Development, Lethbridge, Alberta, Canada. FOODBORNE PATHOGENS AND DISEASE Volume 11, Number 4, 2014 ª Mary Ann Liebert, Inc. DOI: 10.1089/fpd.2013.1621 329