Escherichia coli O157:H7 in Environments of Culture-Positive Cattle

Abstract

Outbreaks of Escherichia coli O157:H7 disease associated with animal exhibits have been reported with increasing frequency. Transmission can occur through contact with contaminated haircoats, bedding, farm structures, or water. We investigated the distribution and survival of E. coli O157:H7 in the immediate environments of individually housed, experimentally inoculated cattle by systematically culturing feed, bedding, water, haircoat, and feed bunk walls for E. coli O157:H7 for 3 months. Cedar chip bedding was the most frequently culture-positive environmental sample tested (27/96 or 28.15%). Among these, 12 (44.0%) of positive bedding samples were collected when the penned animal was fecal culture negative. Survival of E. coli O157:H7 in experimentally inoculated cedar chip bedding and in grass hay feed was determined at different temperatures. Survival was longest in feed at room temperature (60 days), but bacterial counts decreased over time. The possibility that urine plays a role in the environmental survival of E. coli O157:H7 was investigated. Cedar chip bedding moistened with sterile water or bovine urine was inoculated with E. coli O157:H7. Bedding moistened with urine supported growth of E. coli O157:H7, whereas inoculated bedding moistened with only water yielded decreasing numbers of bacteria over time. The findings that environmental samples were frequently positive for E. coli O157:H7 at times when animals were culture negative and that urine provided a substrate for E. coli O157:H7 growth have implications for understanding the on-farm ecology of this pathogen and for the safety of ruminant animal exhibits, particularly petting zoos and farms where children may enter animal pens.

Differences in Colonization and Shedding Patterns after Oral Challenge of Cattle with Three Escherichia coli O157:H7 Strains

“…These findings support the idea that if reoccurring colonization was the cause for intermittent shedding, those patterns most likely resulted from the steers' social interactions and their contact with the ropes, which were considered to be representative of their environment. Several studies have reported that this intermittent environmental exposure can be caused by contaminated water, feed sources, or bedding (15,19,30,48). However, in this study contaminated water was not detected, minimal detection was found in the feed troughs, and no bedding was provided to the steers.…”

Selection Pressure Required for Long-Term Persistence of bla CMY-2 -Positive IncA/C Plasmids

“…If plasmids impose a net fitness cost, then plasmid-free segregants will eventually "sweep" through the population and replace the resistant plasmid-bearing strains. Elimination of resistance genes themselves from a plasmid can lower the fitness burden of a plasmid (3,11), which can also lead to a selective sweep of a less versatile plasmid.…”

Effectiveness of simulated interventions in reducing the estimated prevalence ofE. coliO157:H7 in lactating cows in dairy herds

“…The total effect of increasing the frequency of bedding replacement/cleaning and water trough cleaning is considered a hygienic measure in reducing the prevalence of VTEC O157 infected animals. The data of Scott et al [22] and Davis et al [11] were used to determine the bacterial death rate in water and bedding materials respectively, using formula 1:…”

“…Using formula 1, we estimated that increasing the frequency of replacing bedding (in a straw yard housing system) or cleaning (in a cubicle housing system) from one to two times per week results in a death rate of 0.46 infectious units per day. This was done by fitting an exponential distribution to the data (i.e., initial number of CFU in the environment corresponding to the time unit (day) of the study) reported by Davis et al [11]. Following the same procedure and using the data obtained by Scott et al [22], it was estimated that increasing the frequency of cleaning the water troughs from once per month to four times per month results in a death rate of 0.17 infectious units per day.…”