|EKIRI, ABEL - North Dakota State University|
|LANDBLOM, DOUGLAS - North Dakota State University|
|DOETKOTT, DAWN - North Dakota State University|
|OLET, SUSAN - North Dakota State University|
|KHAITSA, MARGARET - Mississippi State University|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2014
Publication Date: 7/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59601
Citation: Ekiri, A.B., Landblom, D., Doetkott, D., Olet, S., Shelver, W.L., Khaitsa, M.L. 2014. Isolation and characterization of shiga toxin-producing Escherichia coli serogroups O26, O45, O103, O111, O113, O121, O145, and O157 shed from range and feedlot cattle from postweaning to slaughter. Journal of Food Protection. 77(7):1052-1061.
Interpretive Summary: One of the primary causes of foodborne illnesses in humans is caused by Shiga toxin-producing E. coli (STEC), particularly E. coli O157:H7. Increase in infections caused by non-O157:H7 STECs has prompted the US Department of Agriculture, Food Safety and Inspection Service to regulate the presence of STECs belonging to serogroups O26, O45, O103, O111, O121, or O145 in non-intact beef products in 2011. Cattle have been indicated as a natural reservoir for E. coli O157:H7 and non-O157:H7 serogroups. Shiga toxin-producing E. coli present in cattle feces and on the hides during harvest has been linked to beef carcass contamination. The goal of this study was to determine the prevalence of E. coli O157 and non-O157 fecal shedding in cows grazing range pasture and steer calves through the complete production cycle. Findings from the present study suggest that most steer calves on range pasture shed non-O157 STEC at post-weaning and before entry into the finishing stage on feedlots. Intervention strategies aimed at minimizing fecal shedding of non-O157 STEC would likely benefit from targeting the stage before/after weaning. In general, the prevalence of O157 and non-O157 shedding in the present study was higher in cows compared to steers. The most commonly isolated non-O157 STEC serogroup in cows and steers was O103, and the least commonly isolated serogroups were O111 and O113. This study had a number of limitations, however. First, study samples were collected from only one cohort of cattle, as such; extrapolations of this study should consider the potential differences in study populations, as well as differences in geographical locations and laboratory methods used. Second, the occurrence of non-O157 STECs O45, O113, and O121 may have been underestimated because samples were not enriched using immunomagnetic separation due to unavailability of these reagents at the time of study. Enrichment of fecal samples using immunomagnetic separation with serogroup specific beads may have increased the likelihood of isolating these serogroups.
Technical Abstract: Cattle are the main reservoirs for Shiga toxin-producing Escherichia coli (STEC) strains. E. coli O26, O45, O103, O111, O121, O145, and O157 are among the STEC serogroups that cause severe foodborne illness and have been declared as adulterants by the United States Department of Agriculture, Food Safety and Inspection Service. The objectives of this study were (1) to estimate the prevalence of non-O157 STEC and E. coli O157 in naturally infected beef cows, and steer calves at post-weaning, during finishing and at slaughter, and (2) to test non-O157 STEC isolates for the presence of virulence genes, including stx1, stx2, eaeA, and ehlyA. Samples were collected from study animals over multiple sampling periods and included fecal grabs, rectal swabs and mid-line sponge samples. Laboratory culture, polymerase chain reaction (PCR), and multiplex PCR were performed to recover and identify E. coli and the virulence genes. The prevalence of non-O157 STEC (O26, O45, O103, O111, O121, O113 and O145) fecal shedding varied from 8% (4/48) to 39% (15/38) in cows, and from 2% (1/47) to 38% (9/24) in steer calves. The prevalence of E. coli O157 fecal shedding varied from 0% (0/38) to 52% (25/48) in cows, and from 2% (1/47) to 31% (15/48) in steer calves. In steer calves, the prevalence of non-O157 STEC and E. coli O157 was highest at post-weaning, 16% (15/96) and 23% (22/96), respectively. Among the non-O157 STEC isolates, 79% (164/208) had stx1, 79% (165/208) had stx2, 58% (121/208) had both stx1and stx2 genes. The percentage of non-O157 STEC isolates encoding the eaeA gene was low; of the 165 isolates tested, 8 (5%) were positive for eaeA and 135 isolates (82%) were positive for ehlyA. Findings from this study provide further evidence of non-O157 STEC shedding in beef cows and steer calves particularly at the stage of post-weaning and before entry into the feedlot.