Environmental survival of Escherichia coli O157 may play an important role in the persistence and dissemination of this organism on farms. The survival of culturable and infectious E. coli O157 was studied using microcosms simulating cattle water troughs. Culturable E. coli O157 survived for at least 245 days in the microcosm sediments. Furthermore, E. coli O157 strains surviving more than 6 months in contaminated microcosms were infectious to a group of 10-week-old calves. Fecal excretion of E. coli O157 by these calves persisted for 87 days after challenge. Water trough sediments contaminated with feces from cattle excreting E. coli O157 may serve as a long-term reservoir of this organism on farms and a source of infection for cattle.

Although milk and dairy products are important components of a healthy diet, if consumed unpasteurized, they also can present a health hazard due to possible contamination with pathogenic bacteria. These bacteria can originate even from clinically healthy animals from which milk is derived or from environmental contamination occurring during collection and storage of milk. The decreased frequency of bovine carriage of certain zoonotic pathogens and improved milking hygiene have contributed considerably to decreased contamination of milk but have not, and cannot, fully eliminate the risk of milkborne disease. Pasteurization is the most effective method of enhancing the microbiological safety of milk. The consumption of milk that is not pasteurized increases the risk of contracting disease from a foodstuff that is otherwise very nutritious and healthy. Despite concerns to the contrary, pasteurization does not change the nutritional value of milk. Understanding the science behind this controversial and highly debated topic will provide public health care workers the information needed to discern fact from fiction and will provide a tool to enhance communication with clients in an effort to reduce the incidence of infections associated with the consumption of unpasteurized milk and dairy products.

Identification of the sources and methods of transmission of Escherichia coli O157:H7 in feedlot cattle may facilitate the development of on-farm control measures for this important food-borne pathogen. The prevalence of E. coli O157:H7 in fecal samples of commercial feedlot cattle in 20 feedlot pens between April and September 2000 was determined throughout the finishing feeding period prior to slaughter. Using immunomagnetic separation, E. coli O157:H7 was isolated from 636 of 4,790 (13%) fecal samples in this study, with highest prevalence earliest in the feeding period. No differences were observed in the fecal or water trough sediment prevalence values of E. coli O157:H7 in 10 pens supplied with chlorinated drinking water supplies compared with nonchlorinated water pens. Pulsed-field gel electrophoresis of XbaI-digested bacterial DNA of the 230 isolates obtained from eight of the pens revealed 56 unique restriction endonuclease digestion patterns (REDPs), although nearly 60% of the isolates belonged to a group of four closely related genetic subtypes that were present in each of the pens and throughout the sampling period. The other REDPs were typically transiently detected, often in single pens and on single sample dates, and in many cases were also closely related to the four predominant REDPs. The persistence and predominance of a few REDPs observed over the entire feeding period on this livestock operation highlight the importance of the farm environment, and not necessarily the incoming cattle, as a potential source or reservoir of E. coli O157:H7 on farms.Escherichia coli O157:H7 is an important human pathogen worldwide (17, 36). The primary route of human infection is via foods of bovine origin and water contaminated with bovine fecal material (3). Not surprisingly, the prevalence of E. coli O157:H7 contamination on bovine carcass surfaces at slaughter is correlated with the fecal prevalence in the live cattle before slaughter (13). The peak incidence of human disease associated with this pathogen occurs during the summer months, the same season that the prevalence of bovine fecal carriage of this organism is also at its highest (6,20,45). It has been proposed that reducing both the magnitude of fecal excretion and the fecal prevalence of this organism in cattle immediately prior to slaughter could significantly reduce the incidence of human disease associated with this pathogen (24, 31). Unfortunately, methods to reduce the fecal prevalence of E. coli O157:H7 in cattle are not currently available. Given the typically transient fecal shedding of E. coli O157:H7 by cattle, a better understanding of the epidemiology and ecology of E. coli O157, particularly the source of exposure of cattle, may provide valuable information that could be used in the design of preharvest control measures for E. coli O157:H7.The purpose of this study was to determine the pattern of fecal carriage of E. coli O157:H7 in cattle fattened under modern intensive feedlot management conditions. A temporal association between feca...

Shiga toxin-producing Escherichia coli (STEC) strains have been detected in a wide diversity of mammals, birds, fish, and several insects. Carriage by most animals is asymptomatic, thus allowing for dissemination of the bacterium in the environment without detection. Replication of the organism may occur in the gastrointestinal tract of some animals, notably ruminants. Carriage may also be passive or transient, without significant amplification of bacterial numbers while in the animal host. Animals may be classified as reservoir species, spillover hosts, or dead-end hosts. This classification is based on the animal's ability to (i) transmit STEC to other animal species and (ii) maintain STEC infection in the absence of continuous exposure. Animal reservoirs are able to maintain STEC infections in the absence of continuous STEC exposure and transmit infection to other species. Spillover hosts, although capable of transmitting STEC to other animals, are unable to maintain infection in the absence of repeated exposure. The large diversity of reservoir and spillover host species and the survival of the organism in environmental niches result in complex pathways of transmission that are difficult to interrupt.

The antiterminator Q gene of bacteriophage 933W ( Q 933 ) was identified upstream of the stx 2 gene in 90% of human disease–origin Escherichia coli O157:H7 isolates and in 44.5% of bovine isolates. Shiga toxin production was higher in Q 933 -positive isolates than Q 933 -negative isolates. This genetic marker may provide a useful molecular tool for epidemiologic studies.