ARS | Publication request: Longitudinal Study of Escherichia coli O157:H7 in a Beef Cattle Feedlot and the Role of High Shedders in Hide Contamination

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 26, 2009
Publication Date: May 13, 2009
Citation: Arthur, T.M., Keen, J.E., Bosilevac, J.M., Brichta-Harhay, D.M., Kalchayanand, N., Shackelford, S.D., Wheeler, T.L., Nou, X., Koohmaraie, M. 2009. Longitudinal Study of Escherichia coli O157:H7 in a Beef Cattle Feedlot and the Role of High Shedders in Hide Contamination [abstract]. 7th International Symposium on Shiga Toxin (Verocytotoxin)-Producing Escherichia coli Infections (VTEC2009) Paper No. 195.

Technical Abstract: It is now well established that, at the time of harvest, hides are the major source of Escherichia coli O157:H7 contamination on beef carcasses. Thus, reducing the levels of foodborne pathogens on cattle hides has been the focus of many pre- and post-harvest research efforts. In the area of pre-harvest research, several approaches have been taken to reduce the prevalence of E. coli O157:H7 in feces of cattle presented for slaughter. The basis for these approaches is that by reducing fecal pathogen load, the pathogen prevalence and level on hides will be reduced through lower cross-contamination at the feedlot and, subsequently, carcass contamination rates will decrease. However, it is not known what level of pathogen reduction in feces would be necessary to significantly reduce hide and carcass contamination during processing. A key piece of information needed to address this question is an understanding of the number of shedding cattle in a pen needed to contaminate the hides of most of the cattle in that same pen. Aside from the number of cattle shedding the pathogen, the concentration of the pathogen in feces plays a pivotal role in spreading the pathogen between animals. Recently, cattle shedding E. coli O157:H7 at high levels (“super-shedders”) have been associated with high transmission rates. While a number of studies have indicated the importance of super-shedders in fecal transmission dynamics, there is a general lack of information pertaining to the effects of high shedding rates on hide prevalence. The objective of the study described here was two-fold: 1) to determine how animals shedding E. coli O157:H7 at high levels (= 200 CFU/g) affect the prevalence and levels of E. coli O157:H7 on the hides of other animals within the same pen; 2) to investigate the dynamics of E. coli O157:H7 fecal and hide prevalence over a 9-month period. Cattle (n=319) were distributed across ten adjacent pens and fecal and hide levels of E. coli O157:H7 were monitored. The occurrence of one or more high shedding cattle in a pen was strongly associated with increased pen hide prevalence, the odds ratio (OR) was 14.4 (95% CI: 6.5-31.8), increased pen fecal prevalence (OR = 8.8; 95% CI: 4.9-15.8) and increased numbers of cattle with high hide levels of E. coli O157:H7 (= 40 CFU/100 cm2) in the pen (OR = 17.7; 95% CI: 6.5-47.8). The occurrence of one or more high fecal shedding cattle in a pen was strongly associated with the outcome of one or more cattle in a pen with high hide levels of E. coli O157:H7 (OR = 72.9; 95% CI: 18.7-284). Logistic regression models support the hypothesis that high level fecal shedding prevalence (termed “super-shedders”) is associated with hide and high level hide contamination of cattle. Large and unpredictable fluctuations within and between pens in both fecal and hide prevalence of E. coli O157:H7 were detected and should be used as a guide when designing pre-harvest studies.