The Effect of Dietary Protein, Fiber, and Dig es ta Passage Rate on the Duration and Concentration of Escherichia coli 0157:H7 Shed by Cattle

Infection with E. coli O157:H7 is the most common cause of human hemorrhagic colitis in North America. Cattle are a reservoir for this human pathogen and individual animals are sporadically and transiently colonized. We hypothesize that pre-harvest dietary management may reduce the risk of E. coli O157positive animals entering our food chain. The effect of dietary energy, fiber, and digesta passage rates on the duration and concentration of fecal E. coli 0157 was determined. Sixteen healthy Charlais x Hereford or Holstein heifers were acclimated to one of four diets: a finishing diet (high in energy and low in fiber), a growing diet (low in energy and high in fiber), chopped alfalfa (small particle size), or long alfalfa (large particle size). A single oral dose of 1010 colony forming-units of E.coli 0157 was administered to each animal and fecal samples were cultured for the bacteria by selective-enrichment twice a week for the duration of the study. No significant difference in the shedding of 0157 by animals on the finishing or growing diet was observed. However, withholding feed of either type, for 24 hours, did increase the concentration of the bacteria in the fecal material of about half of the animals . A significant correlation (p value=0.008) was observed between digesta passage rate and the duration of fecal E. coli 0157. Animals with slower passage rates of 2 to 3 % per hour cleared E. coli 0157 from their intestinal tract in 10 days or less compared to animals with digesta passage rates of 4 to 5 % per hour who shed the bacteria for more than 69 days. These results show that cattle diet influences the duration and concentration of fecal E. coli O157:H7. SEPTEMBER, 1998 Introduction Escherichia coli O157:H7 , a member of the enterohemorrhagic E. coli (EHEC), has been implicated as the most common causative agent of hemorrhagic colitis (HC) in the United States, since 1982. 15,21 •34•36 Approximately 2-15% ofHC cases progress to serious nonintestinal sequelae as the hemolytic uremic syndrome (HUS) or thrombotic thrombocytopenic purpura (TTP).4•15,40 HUS, characterized by thrombocytopenia and microangiopathic anemia, is the most common cause of acute renal failure in children, and has a mortality rate of 5-10%. 4·15•16•36 TTP shares many clinical manifestations with HUS but primarily affects the elderly and has a mortality rate near 50%.4 •36,40 E. coli O157:H7 infections occur worldwide. A recent outbreak in Japan, caused by contaminated radish sprouts, affected more than 10,000 school children and resulted in 13 deaths.31•37•40 An outbreak in Scotland, linked to contaminated beef and gravy, affected more than 400 individuals and resulted in 16 deaths.40 Most human EHEC infection results from the ingestion of contaminated bovine food products such as undercooked ground beef or unpasteurized dairy products .4•15•32 In addition, contaminated water, fresh vegetables, and unpasteurized apple juice have also been implicated as sources of infection and in some of these cases the source of contamination is known to be bovine feces .2·6•23,36,38 Economic impact of contaminated bovine products has been enormous and includes product recalls and caused the closure of one processing plant.7 Ruminants are reservoirs for E. coli O157:H7. We and others have suggested that preharvest management of ruminants may decrease the number of E. coli