Horizontal transmission of Escherichia coli O157:H7 during cattle housing

Transmission on empirical dynamic contact networks is influenced by data processing decisions

Dynamic contact data can be used to inform disease transmission models, providing insight into the dynamics of infectious diseases. Such data often requires extensive processing for use in models or analysis. Therefore, processing decisions can potentially influence the topology of the contact network and the simulated disease transmission dynamics on the network. In this study, we examine how four processing decisions, including temporal sampling window (TSW), spatial threshold of contact (SpTh), minimum contact duration (MCD), and temporal aggregation (daily or hourly) influence the information content of contact data (indicated by changes in entropy) as well as disease transmission model dynamics. We found that changes made to information content by processing decisions translated to significant impacts to the transmission dynamics of disease models using the contact data. In particular, we found that SpTh had the largest independent influence on information content, and that some output metrics (R₀, time to peak infection) were more sensitive to changes in information than others (epidemic extent). These findings suggest that insights gained from transmission modeling using dynamic contact data can be influenced by processing decisions alone, emphasizing the need to carefully consideration them prior to using contact-based models to conduct analyses, compare different datasets, or inform policy decisions.

Assessing Transmission of Antimicrobial-Resistant Escherichia coli in Wild Giraffe Contact Networks

There is growing evidence that anthropogenic sources of antibiotics and antimicrobial-resistant bacteria can spill over into natural ecosystems, raising questions about the role wild animals play in the emergence, maintenance, and dispersal of antibiotic resistance genes. In particular, we lack an understanding of how resistance genes circulate within wild animal populations, including whether specific host characteristics, such as social associations, promote interhost transmission of these genes. In this study, we used social network analysis to explore the forces shaping population-level patterns of resistant Escherichia coli in wild giraffe (Giraffa camelopardalis) and assess the relative importance of social contact for the dissemination of resistant E. coli between giraffe. Of 195 giraffe sampled, only 5.1% harbored E. coli isolates resistant to one or more tested antibiotics. Whole-genome sequencing on a subset of resistant isolates revealed a number of acquired resistance genes with linkages to mobile genetic elements. However, we found no evidence that the spread of resistance genes among giraffe was facilitated by interhost associations. Giraffe with lower social degree were more likely to harbor resistant E. coli, but this relationship was likely driven by a correlation between an individual's social connectedness and age. Indeed, resistant E. coli was most frequently detected in socially isolated neonates, indicating that resistant E. coli may have a selective advantage in the gastrointestinal tracts of neonates compared to other age classes. Taken together, these results suggest that the maintenance of antimicrobial-resistant bacteria in wild populations may, in part, be determined by host traits and microbial competition dynamics within the host.IMPORTANCE Antimicrobial resistance represents a significant threat to human health, food security, and the global economy. To fully understand the evolution and dissemination of resistance genes, a complete picture of antimicrobial resistance in all biological compartments, including natural ecosystems, is required. The environment and wild animals may act as reservoirs for anthropogenically derived resistance genes that could be transferrable to clinically relevant bacteria of humans and domestic animals. Our study investigated the possible transmission mechanisms for antimicrobial-resistant bacteria within a wild animal population and, more broadly, contributes to our understanding of how resistance genes are spread and maintained in natural ecosystems.

Investigating behavioral drivers of seasonal Shiga-Toxigenic Escherichia Coli (STEC) patterns in grazing cattle using an agent-based model

The causes of seasonal variability in pathogen transmission are not well understood, and have not been comprehensively investigated. In an example for enteric pathogens, incidence of Escherichia coli O157 (STEC) colonization in cattle is consistently higher during warmer months compared to cooler months in various cattle production systems. However, actual mechanisms for this seasonality remain elusive. In addition, the influence of host (cattle) behavior on this pattern has not been thoroughly considered. To that end, we constructed a spatially explicit agent-based model that accounted for the effect of temperature fluctuations on cattle behavior (direct contact among cattle and indirect between cattle and environment), as well as its effect on pathogen survival in the environment. We then simulated the model in a factorial approach to evaluate the hypothesis that temperature fluctuations can lead to seasonal STEC transmission dynamics by influencing cattle aggregation, grazing, and drinking behaviors. Simulation results showed that higher temperatures increased the frequency at which cattle aggregated under shade in pasture, resulting in increased direct contact and transmission of STEC between individual cattle, and hence higher incidence over model simulations in the warm season. In contrast, increased drinking behavior during warm season was not an important transmission pathway. Although sensitivity analyses suggested that the relative importance of direct vs. indirect (environmental) pathways depend to upon model parameterization, model simulations indicated that factors influencing cattle aggregation, such as temperature, were likely strong drivers of transmission dynamics of enteric pathogens.

The effect of transportation and lairage on faecal shedding and carcass contamination with Escherichia coli O157 and O26 in very young calves in New Zealand

The effect of transportation and lairage on the faecal shedding and post-slaughter contamination of carcasses with Escherichia coli O157 and O26 in young calves (4-7-day-old) was assessed in a cohort study at a regional calf-processing plant in the North Island of New Zealand, following 60 calves as cohorts from six dairy farms to slaughter. Multiple samples from each animal at pre-slaughter (recto-anal mucosal swab) and carcass at post-slaughter (sponge swab) were collected and screened using real-time PCR and culture isolation methods for the presence of E. coli O157 and O26 (Shiga toxin-producing E. coli (STEC) and non-STEC). Genotype analysis of E. coli O157 and O26 isolates provided little evidence of faecal-oral transmission of infection between calves during transportation and lairage. Increased cross-contamination of hides and carcasses with E. coli O157 and O26 between co-transported calves was confirmed at pre-hide removal and post-evisceration stages but not at pre-boning (at the end of dressing prior to chilling), indicating that good hygiene practices and application of an approved intervention effectively controlled carcass contamination. This study was the first of its kind to assess the impact of transportation and lairage on the faecal carriage and post-harvest contamination of carcasses with E. coli O157 and O26 in very young calves.

Frequency and risk-factors analysis of Escherichia coli O157:H7 in Bali-cattle

Cattle are known as the main reservoir of zoonotic agents verocytotoxin-producing Escherichia coli. These bacteria are usually isolated from calves with diarrhea and/or mucus and blood. Tolerance of these agents to the environmental conditions will strengthen of their transmission among livestock. A total of 238 cattle fecal samples from four sub-districts in Badung, Bali were used in this study. Epidemiological data observed include cattle age, sex, cattle rearing system, the source of drinking water, weather, altitude, and type of cage floor, the cleanliness of cage floor, the slope of cage floor, and the level of cattle cleanliness. The study was initiated by culturing of samples onto eosin methylene blue agar, then Gram stained, and tested for indole, methyl-red, voges proskauer, and citrate, Potential E.coli isolates were then cultured onto sorbitol MacConkey agar, and further tested using O157 latex agglutination test and H7 antisera. Molecular identification was performed by analysis of the 16S rRNA gene, and epidemiological data was analyzed using STATA 12.0 software. The results showed, the prevalence of E. coli O157:H7 in cattle at Badung regency was 6.30% (15/238) covering four sub districts i.e. Petang, Abiansemal, Mengwi, and Kuta which their prevalence was 8.62%(5/58), 10%(6/60), 3.33%(2/60), and 3.33(2/60)%, respectively. The analysis of 16S rRNA gene confirmed of isolates as an E. coli O157:H7 strain with 99% similarities. Furthermore, the risk factors analysis showed that the slope of the cage floor has a highly significant effect (P<0.05) to the distribution of infection. Consequently, implementing this factor must be concerned in order to decrease of infection.

Reducing Foodborne Pathogen Persistence and Transmission in Animal Production Environments: Challenges and Opportunities

Preharvest strategies to reduce zoonotic pathogens in food animals are important components of the farm-to-table food safety continuum. The problem is complex; there are multiple pathogens of concern, multiple animal species under different production and management systems, and a variety of sources of pathogens, including other livestock and domestic animals, wild animals and birds, insects, water, and feed. Preharvest food safety research has identified a number of intervention strategies, including probiotics, direct-fed microbials, competitive exclusion cultures, vaccines, and bacteriophages, in addition to factors that can impact pathogens on-farm, such as seasonality, production systems, diet, and dietary additives. Moreover, this work has revealed both challenges and opportunities for reducing pathogens in food animals. Animals that shed high levels of pathogens and predominant pathogen strains that exhibit long-term persistence appear to play significant roles in maintaining the prevalence of pathogens in animals and their production environment. Continued investigation and advancements in sequencing and other technologies are expected to reveal the mechanisms that result in super-shedding and persistence, in addition to increasing the prospects for selection of pathogen-resistant food animals and understanding of the microbial ecology of the gastrointestinal tract with regard to zoonotic pathogen colonization. It is likely that this continued research will reveal other challenges, which may further indicate potential targets or critical control points for pathogen reduction in livestock. Additional benefits of the preharvest reduction of pathogens in food animals are the reduction of produce, water, and environmental contamination, and thereby lower risk for human illnesses linked to these sources.

Perspectives on super-shedding of Escherichia coli O157:H7 by cattle

Escherichia coli O157:H7 is a foodborne pathogen that causes illness in humans worldwide. Cattle are the primary reservoir of this bacterium, with the concentration and frequency of E. coli O157:H7 shedding varying greatly among individuals. The term "super-shedder" has been applied to cattle that shed concentrations of E. coli O157:H7 ≥ 10⁴ colony-forming units/g feces. Super-shedders have been reported to have a substantial impact on the prevalence and transmission of E. coli O157:H7 in the environment. The specific factors responsible for super-shedding are unknown, but are presumably mediated by characteristics of the bacterium, animal host, and environment. Super-shedding is sporadic and inconsistent, suggesting that biofilms of E. coli O157:H7 colonizing the intestinal epithelium in cattle are intermittently released into feces. Phenotypic and genotypic differences have been noted in E. coli O157:H7 recovered from super-shedders as compared to low-shedding cattle, including differences in phage type (PT21/28), carbon utilization, degree of clonal relatedness, tir polymorphisms, and differences in the presence of stx2a and stx2c, as well as antiterminator Q gene alleles. There is also some evidence to support that the native fecal microbiome is distinct between super-shedders and low-shedders and that low-shedders have higher levels of lytic phage within feces. Consequently, conditions within the host may determine whether E. coli O157:H7 can proliferate sufficiently for the host to obtain super-shedding status. Targeting super-shedders for mitigation of E. coli O157:H7 has been proposed as a means of reducing the incidence and spread of this pathogen to the environment. If super-shedders could be easily identified, strategies such as bacteriophage therapy, probiotics, vaccination, or dietary inclusion of plant secondary compounds could be specifically targeted at this subpopulation. Evidence that super-shedder isolates share a commonality with isolates linked to human illness makes it imperative that the etiology of this phenomenon be characterized.

Veterinary Public Health Approach to Managing Pathogenic Verocytotoxigenic Escherichia coli in the Agri-Food Chain

Verocytoxigenic Escherichia coli (VTEC) comprises many diverse serogroups, but seven serogroups, O157, O26, O103, O145, O111, O21, and O45, have been most commonly linked to severe human infections, though illness has also been reported from a range of other VTEC serogroups. This poses challenges in assessing the risk to humans from the diverse range of VTEC strains that may be recovered from animals, the environment, or food. For routine assessment of risk posed by VTEC recovered from the agri-food chain, the concept of seropathotype can be used to rank the human risk potential from a particular VTEC serogroup on the basis of both serotype (top seven serogroups) and the presence of particular virulence genes (vt in combination with eae, or aaiC plus aggR). But for other VTEC serogroups or virulence gene combinations, it is not currently possible to fully assess the risk posed. VTEC is shed in animal feces and can persist in the farm environment for extended periods ranging from several weeks to many months, posing an ongoing reservoir of contamination for grazing animals, water courses, and fresh produce and for people using farmland for recreational purposes. Appropriate handling and treatment of stored animal waste (slurries and manures) will reduce risk from VTEC in the farm environment. Foods of animal origin such as milk and dairy products and meat may be contaminated with VTEC during production and processing, and the pathogen may survive or grow during processing operations, highlighting the need for well-designed and validated Hazard Analysis Critical Control Point management systems. This article focuses on a veterinary public health approach to managing VTEC, highlighting the various routes in the agri-food chain for transmission of human pathogenic VTEC and general approaches to managing the risk.

Meat Science and Muscle Biology Symposium: Development of bacteriophage treatments to reduce Escherichia coli O157:H7 contamination of beef products and produce

Escherichia coli O157:H7 remains a foodborne pathogen of concern with infections associated with products ranging from ground beef to produce to processed foods. We previously demonstrated that phage-based technologies could reduce foodborne pathogen colonization in live animals. Here, we examined if a 3-phage cocktail could reduce E. coli O157:H7 in experimentally contaminated ground beef, spinach, and cheese. The 3 phages were chosen from our E. coli O157:H7 phage library based on their distinct origins of isolation, lytic ranges, and rapid growth (40- to 50-min life cycle). Two phages belonged to the Myoviridae family and the other phage belonged to the Siphoviridae family. The phage cocktail was added to ground beef, spinach leaves, and cheese slices contaminated with E. coli O157:H7 (10(7) cfu) at a multiplicity of infection of 1. Phage treatment reduced (P < 0.05) the concentrations of E. coli O157:H7 by 1.97 log10 cfu/mL in ground beef when stored at room temperature (24 °C) for 24 h, 0.48 log10 cfu/mL at refrigeration (4 °C), and 0.56 log10 cfu/mL in undercooked condition (internal temperature of 46 °C). Likewise, phage treatment reduced (P < 0.05) E. coli O157:H7 by 3.28, 2.88, and 2.77 log10 cfu/mL in spinach when stored at room temperature for 24, 48, and 72 h, respectively. Phage treatment, however, did not reduce E. coli O157:H7 concentrations in contaminated cheese. Additionally, 3 phage-resistant E. coli O157:H7 strains (309-PR [phage resistant] 1, 309-PR4, and 502-PR5) were isolated and characterized to test if phage resistance could limit long-term use of phages as biocontrol agents. Growth kinetics and adsorption assays indicated that phage resistance in strains 309-PR4 and 502-PR5 was mediated, at least in part, by prevention of phage adsorption. Phage resistance in strain 309-PR1 was the result of limited phage proliferation. Phage resistance was stably maintained in vitro throughout a 4-d subculture period in the absence of phage. No significant reductions in bacterial growth or cell adhesion were observed in resistant strains. Taken together, our results provide additional support for the use of phage to control E. coli O157:H7 in food products; however, the emergence of phage-resistant bacteria could limit the efficacy of phage products. Therefore, further studies are needed to develop resistance mitigation strategies to optimize phage-based technologies.

Cattle Production Systems: Ecology of Existing and Emerging Escherichia coli Types Related to Foodborne Illness

Shiga toxin–producing Escherichia coli (STEC), particularly STEC O157, cause rare but potentially serious human infections. Infection with STEC occurs by fecal-oral transmission, most commonly through food. Cattle are the most important reservoir for human STEC exposure, and efforts to control the flow of STEC through beef processing have reduced rates of human illness. However, further reduction in human incidence of STEC may require control of the pathogen in cattle populations. The ecology of STEC in cattle production systems is complex and explained by factors that favor (a) colonization in the gut, (b) survival in the environment, and (c) ingestion by another cattle host. Although nature creates seasonal environmental conditions that do not favor STEC transmission in cattle, human efforts to control STEC by environmental manipulation have not succeeded. Vaccines and direct-fed microbial products have reduced the carriage of STEC by cattle, and other interventions are under investigation.

Transit effects on fecal Escherichia coli O157 prevalence and coliform concentrations in feedlot cattle

Our objectives were to evaluate the effects of transportation and lairage on fecal shedding of Escherichia coli O157 (E. coli O157), total Escherichia coli, and total coliforms in feedlot cattle, and the relationships between E. coli O157 prevalence and total E. coli population. The study was a randomized complete block design with a split-plot including 2 treatments: a nontransported group, which remained in its pen at all times, and a transported group, which was transported for 1 h in a trailer and subsequently unloaded in a different pen. The experiment was repeated on 3 different days (blocking factor) with 20 steers/d (10 steers/treatment, 60 total). Fecal samples were taken pretransport (h 0) and after 4 and 28 h, lairage from freshly voided fecal pats were taken from each animal. One gram of feces was transferred to a PBS tube, serially diluted, and plated onto Petrifilm for enumeration of total coliforms. Another sample (1 g) was added to gram-negative broth containing cefixime, cefsulodin, and vancomycin, and subjected to immunomagnetic separation. Resulting beads were plated onto MacConkey agar with sorbitol, cefixime, and tellurite. Nonsorbitol fermenting colonies were selected and tested for indole production and O157 antigen agglutination. Results were confirmed using an API 20E kit. Prevalence of E. coli O157 was transient across blocks. E. coli O157 prevalence revealed no treatment × sampling time interaction (P = 0.179) or sampling time effect (P = 0.937), but a tendency for a treatment effect (P = 0.092). Numbers of E. coli and other coliforms did not change across blocks. No effect of treatment (P > 0.7) was observed on total E. coli concentrations or total coliforms. However, tendencies for treatment × sampling time interactions were observed on both populations (P < 0.08), as well as a tendency for a sampling time effect on total E. coli (P = 0.087) and an effect on total coliforms (P = 0.004). Prevalence of E. coli O157 was not correlated with the concentration of total E. coli (P = 0.954). Results suggest that shedding of E. coli O157 and coliforms can vary within a period of 29 h. Greater statistical power and pathogen quantification, as well as hide sampling and stress-related measurements, are needed to be able to conclude on the effects of transport stress on E. coli O157 prevalence and the changes undergone in pathogen shedding patterns after transportation.

Assessment of virulence factors characteristic of human Escherichia coli pathotypes and antimicrobial resistance in O157:H7 and non-O157:H7 isolates from livestock in Spain

The distribution of virulence factors (VFs) typical of diarrheagenic Escherichia coli and the antimicrobial resistance (AMR) profiles were assessed in 780 isolates from healthy pigs, broilers, and cattle from Spain. VF distribution was broader than expected, although at low prevalence for most genes, with AMR being linked mainly to host species.

Genetic diversity and antimicrobial resistance among isolates of Escherichia coli O157: H7 from feces and hides of super-shedders and low-shedding pen-mates in two commercial beef feedlots

Background

Cattle shedding at least 10⁴ CFU Escherichia coli O157:H7/g feces are described as super-shedders and have been shown to increase transmission of E. coli O157:H7 to other cattle in feedlots. This study investigated relationships among fecal isolates from super-shedders (n = 162), perineal hide swab isolates (PS) from super-shedders (n = 137) and fecal isolates from low-shedder (< 10⁴ CFU/g feces) pen-mates (n = 496) using pulsed-field gel electrophoresis (PFGE). A subsample of these fecal isolates (n = 474) was tested for antimicrobial resistance. Isolates of E. coli O157:H7 were obtained from cattle in pens (avg. 181 head) at 2 commercial feedlots in southern Alberta with each steer sampled at entry to the feedlot and prior to slaughter.

Results

Only 1 steer maintained super-shedder status at both samplings, although approximately 30% of super-shedders in sampling 1 had low-shedder status at sampling 2. A total of 85 restriction endonuclease digestion clusters (REPC; 90% or greater similarity) and 86 unique isolates (< 90% similarity) were detected, with the predominant REPC (30% of isolates) being isolated from cattle in all feedlot pens, although it was not associated with shedding status (super- or low-shedder; P = 0.94). Only 2/21 super-shedders had fecal isolates in the same REPC at both samplings. Fecal and PS isolates from individual super-shedders generally belonged to different REPCs, although fecal isolates of E. coli O157:H7 from super- and low-shedders showed greater similarity (P < 0.001) than those from PS. For 77% of super-shedders, PFGE profiles of super-shedder fecal and PS isolates were distinct from all low-shedder fecal isolates collected in the same pen. A low level of antimicrobial resistance (3.7%) was detected and prevalence of antimicrobial resistance did not differ among super- and low-shedder isolates (P = 0.69), although all super-shedder isolates with antimicrobial resistance (n = 3) were resistant to multiple antimicrobials.

Conclusions

Super-shedders did not have increased antimicrobial resistance compared to low-shedder pen mates. Our data demonstrated that PFGE profiles of individual super-shedders varied over time and that only 1/162 steers remained a super-shedder at 2 samplings. In these two commercial feedlots, PFGE subtypes of E. coli O157:H7 from fecal isolates of super- and low-shedders were frequently different as were subtypes of fecal and perineal hide isolates from super-shedders.

The strain-specific dynamics of Escherichia coli O157:H7 faecal shedding in cattle post inoculation

This study reports analysis of faecal shedding dynamics in cattle for three Escherichia coli O157:H7 (ECO157) strains (S1, S2 and S3) of different genotype and ecological history, using experimental inoculation data. The three strains were compared for their shedding frequency and level of ECO157 in faeces. A multistate Markov chain model was used to compare shedding patterns of S1 and S2. Strains S1 and S2 were detected seven to eight times more often and at 10(4) larger levels than strain S3. Strains S1 and S2 had similar frequencies and levels of shedding. However, the total time spent in the shedding state during colonization was on average four times longer for S1 (15 days) compared to S2 (4 days). These results indicate that an ECO157 strain effect on the frequency, level, pattern and the duration of faecal shedding may need to be considered in control of ECO157 in the cattle reservoir.

Escherichia coli O157:H7: animal reservoir and sources of human infection

This review surveys the literature on carriage and transmission of enterohemorrhagic Escherichia coli (EHEC) O157:H7 in the context of virulence factors and sampling/culture technique. EHEC of the O157:H7 serotype are worldwide zoonotic pathogens responsible for the majority of severe cases of human EHEC disease. EHEC O157:H7 strains are carried primarily by healthy cattle and other ruminants, but most of the bovine strains are not transmitted to people, and do not exhibit virulence factors associated with human disease. Prevalence of EHEC O157:H7 is probably underestimated. Carriage of EHEC O157:H7 by individual animals is typically short-lived, but pen and farm prevalence of specific isolates may extend for months or years and some carriers, designated as supershedders, may harbor high intestinal numbers of the pathogen for extended periods. The prevalence of EHEC O157:H7 in cattle peaks in the summer and is higher in postweaned calves and heifers than in younger and older animals. Virulent strains of EHEC O157:H7 are rarely harbored by pigs or chickens, but are found in turkeys. The bacteria rarely occur in wildlife with the exception of deer and are only sporadically carried by domestic animals and synanthropic rodents and birds. EHEC O157:H7 occur in amphibian, fish, and invertebrate carriers, and can colonize plant surfaces and tissues via attachment mechanisms different from those mediating intestinal attachment. Strains of EHEC O157:H7 exhibit high genetic variability but typically a small number of genetic types predominate in groups of cattle and a farm environment. Transmission to people occurs primarily via ingestion of inadequately processed contaminated food or water and less frequently through contact with manure, animals, or infected people.

Super shedding of Escherichia coli O157:H7 by cattle and the impact on beef carcass contamination

Beef carcass contamination is a direct result of pathogen transfer from cattle hides harboring organisms such as enterohemorrhagic Escherichia coli. Hide contamination occurs from direct and indirect fecal contamination in cattle production and lairage environments. In each of these environments, individual animals shedding E. coli O157:H7 at high levels (>10(4) CFU/g of feces, hereafter referred to as "super shedders") can have a disproportionate effect on cattle hide and subsequent carcass contamination. It is not known what criteria must be met to cause an animal to shed at levels exceeding 10(4) CFU/g. Understanding the factors that play a role in super shedding will aid in minimizing or eliminating the super shedding population. Interventions that would prevent super shedding in the cattle population should reduce E. coli O157:H7 transmission in the production and lairage environments resulting in reduced risk of beef carcass contamination and a safer finished product.

In vivo and ex vivo evaluations of bacteriophages e11/2 and e4/1c for use in the control of Escherichia coli O157:H7

This study investigated the effect of bacteriophages (phages) e11/2 and e4/1c against Escherichia coli O157:H7 in an ex vivo rumen model and in cattle in vivo. In the ex vivo rumen model, samples were inoculated with either 10³ or 10⁶ CFU/ml inoculum of E. coli O157:H7 and challenged separately with each bacteriophage. In the presence of phage e11/2, the numbers of E. coli O157:H7 bacteria were significantly (P < 0.05) reduced to below the limit of detection within 1 h. Phage e4/1c significantly (P < 0.05) reduced E. coli O157:H7 numbers within 2 h of incubation, but the number of surviving E. coli O157:H7 bacteria then remained unchanged over a further 22-h incubation period. The ability of a phage cocktail of e11/2 and e4/1c to reduce the fecal shedding of E. coli O157:H7 in experimentally inoculated cattle was then investigated in two cattle trials. Cattle (yearlings, n = 20 for trial one; adult fistulated cattle, n = 2 for trial two) were orally inoculated with 10(10) CFU of E. coli O157:H7. Animals (n = 10 for trial one; n = 1 for trial two) were dosed daily with a bacteriophage cocktail of 10(11) PFU for 3 days postinoculation. E. coli O157:H7 and phage numbers in fecal and/or rumen samples were determined over 7 days postinoculation. E. coli O157:H7 numbers rapidly declined in all animals within 24 to 48 h; however, there was no significant difference (P > 0.05) between the numbers of E. coli O157:H7 bacteria shed by the phage-treated or control animals. Phages were recovered from the rumen but not from the feces of the adult fistulated animal in trial two but were recovered from the feces of the yearling animals in trial one. While the results from the rumen model suggest that phages are effective in the rumen, further research is required to improve the antimicrobial effectiveness of phages for the elimination of E. coli O157:H7 in vivo.

Use of model super-shedders to define the role of pen floor and hide contamination in the transmission of Escherichia coli O157:H7

Super-shedders, cattle shedding at least 10(4) cfu of Escherichia coli O157:H7 per gram of feces, increase the risks of contaminating the food chain and disseminating the organism through cattle populations. Because detecting super-shedders in cattle populations is laborious and time-consuming, a study was conducted to evaluate the role of hide and pen-floor contamination by model super shedders (MSS) in transmission of E. coli O157:H7. Steers (n = 48) negative for E. coli O157:H7 were allocated to 6 pens, with 2 replicate pens per treatment. Treatment A consisted of 3,000 g of feces inoculated with 10(6) cfu/g of a 5-strain mixture of nalidixic acid-resistant E. coli O157:H7 and spread in simulated fecal pats on the pen floor for d 0 through 4 and d 14 through 18. For treatment B, 100 g of the feces per day was spread on the perineum of 1 MSS per pen, and the remaining feces was placed on the pen floor as fecal pats similar to treatment A. Treatment C differed from B in that 50 g of feces was spread on the perineum and 50 g on the brisket of the MSS steer. Fecal samples, perineal swabs (500-cm(2) area around the anus), freshly voided fecal pats and manila rope samples were collected during a 56-d experimental period. More positive rope samples were found in treatments B and C compared with A (P = 0.05), and steers within treatments B and C were 1.3 times more likely (P = 0.05) to shed E. coli O157:H7 in their feces than steers in treatment A. Even though the number of E. coli O157:H7 introduced into pens was similar, results indicate an increased importance of hide compared with pen-floor contamination for transmission of this organism to cattle. Because cattle within treatment B were persistently colonized with E. coli O157:H7, this design should prove suitable for future studies investigating the role of super-shedders in the transmission of E. coli O157:H7.

Soil versus Pond Ash Surfacing of Feedlot Pens: Occurrence of Escherichia coli O157:H7 in Cattle and Persistence in Manure

Reducing Escherichia coli O157:H7 in cattle and their manure is critical for reducing the risk for human foodborne and waterborne illness. The objective of this study was to evaluate the effects of soil and pond ash surfaces for feedlot pens on the prevalence, levels, and/or persistence of naturally occurring E. coli O157:H7 and total E. coli in cattle (feces and hides) and manure. Cattle (128 beef heifers) were sorted among 16 pens: 8 surfaced with soil and 8 surfaced with pond ash. The prevalence of E. coli O157:H7 in feces decreased (P < 0.0001) during the study from 57.0% on day 0 to 3.9% on day 84 but did not differ (P > or = 0.05) between cattle on soil and on pond ash pens at any sampling period. The prevalence of the pathogen on hides and in feedlot surface material (FSM) also decreased (P < 0.0001), with no effect of soil or pond ash surface (P > or = 0.05). Similarly, levels of E. coli in FSM did not differ (P > or = 0.05) at any sampling period, and there were no clear trends for survival differences of E. coli O157:H7 or E. coli in FSM between pond ash and soil surfaces, although E. coli populations survived at 5.0 log CFU/g of FSM on the pen surfaces 6 weeks after the cattle were removed. These results indicate that housing cattle on pens surfaced with pond ash versus pens surfaced with soil does not affect E. coli O157:H7 in cattle or their manure.

Longitudinal study of Escherichia coli O157:H7 in a beef cattle feedlot and role of high-level shedders in hide contamination

The objectives of the study described here were (i) to investigate the dynamics of Escherichia coli O157:H7 fecal and hide prevalence over a 9-month period in a feedlot setting and (ii) to determine how animals shedding E. coli O157:H7 at high levels affect the prevalence and levels of E. coli O157:H7 on the hides of other animals in the same pen. Cattle (n = 319) were distributed in 10 adjacent pens, and fecal and hide levels of E. coli O157:H7 were monitored. When the fecal pen prevalence exceeded 20%, the hide pen prevalence was usually (25 of 27 pens) greater than 80%. Sixteen of 19 (84.2%) supershedder (>10(4) CFU/g) pens had a fecal prevalence greater than 20%. Significant associations with hide and high-level hide (>/=40 CFU/100 cm(2)) contamination were identified for (i) a fecal prevalence greater than 20%, (ii) the presence of one or more high-density shedders (>/=200 CFU/g) in a pen, and (iii) the presence of one or more supershedders in a pen. The results presented here suggest that the E. coli O157:H7 fecal prevalence should be reduced below 20% and the levels of shedding should be kept below 200 CFU/g to minimize the contamination of cattle hides. Also, 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 preharvest studies, particularly preharvest intervention studies, are designed.

Factors associated with cross-contamination of hides of Scottish cattle by Escherichia coli O157

The putative source of hide contamination for 236 cattle in Scotland followed from the farm through to slaughter was determined using phage and verocytotoxin type data. The majority of cattle (84%) were found to have subtypes of Escherichia coli O157 on their hide that had not been found previously in any animal from the farm of origin, strongly suggesting that contamination occurred once animals had left the farm of origin. Using logistic regression analysis, several variables and factors were found to be strongly associated (P < 0.01) with cross-contamination of cattle hides at the univariate level; commercial transport to slaughter, transport with other animals, use of a crush, line automation, and increasing slaughterhouse throughput were all risk factors, while feeding hay in lairage, processing an animal earlier in a slaughter cohort, and cleaning the landing area poststunning were protective. In the multivariable model, with the slaughterhouse and the farm group included as random effects, factors associated with the cross-contamination of cattle hides were identified. Transport to the slaughterhouse by a commercial hauler had a borderline-significant association with increased odds of an animal having a cross-contaminated hide (odds ratio [OR] [95% confidence interval (CI)] = 5.7 [0.99, 33.0]; P = 0.05). At the slaughterhouse, providing hay to cattle waiting in lairage (OR [95% CI] = 0.04 [<0.01, 1.04]; P = 0.05) and cleaning the landing area (OR [95% CI] = 0.03 [<0.01, 1.15,]; P = 0.06) also had a borderline-significant association with decreased odds of an animal having a cross-contaminated hide. Although the prevalence of carcass contamination remains very low, targeted intervention at the preslaughter stage may have the potential to reduce further the risk to public health.

Prevalence and molecular characterization of Escherichia coli O157:H7 on Irish lamb carcasses, fleece and in faeces samples

AIMS

To determine the prevalence, seasonal variation and virulence characteristics of Escherichia coli O157:H7 in lambs presented for slaughter in Ireland.

METHODS AND RESULTS

Over a 13-month period, pre- and postchill carcass swabs, faeces and fleece samples from 1600 lambs were examined for the presence of E. coli O157:H7. Escherichia coli O157:H7 was isolated from 5.75% (23/400) of fleece samples, 1.5% (6/400) of pre- and 1% (4/400) of postchill carcass swabs but was not isolated in faeces (0/400). The present study detected no evidence of seasonal variation. Polymerase chain reaction analysis showed that both the vt1 and vt2 genes associated with clinical illness were carried by five of the E. coli O157:H7 isolates, while 24 of the remaining isolates carried the vt2 gene only. Phage typing detected four different subtypes: PT 32 (48.48%), PT 8 (12.12%), PT 31 (12.12%) and PT 21/28 (12.12%).

CONCLUSIONS

Escherichia coli O157:H7 is present in lambs at slaughter in Irish abattoirs and the virulence profiles of these isolates reveals that they are potentially harmful to humans.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study provides crucial information indicating that sheep may be a significant contributing source to human E. coli O157:H7 infection.

Development of an experimental model to assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder within a feedlot environment

This study was conducted to develop an experimental model that could assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder (>10(4) CFU/g of feces) within a feedlot environment. The day before the study began, 48 steers that had been negative for E. coli O157:H7 in feces for three consecutive weeks were sorted into three treatment groups, with two replicate pens per treatment and 8 steers per pen. Steers within the pens (20.50 by 10.75 m) were exposed to control feces or feces inoculated with two levels of a mixture of five strains of nalidixic acid-resistant E. coli O157:H7 (low level, 10(2) CFU/g; high level, 10(5) CFU/g). Five 300-g fecal pats were introduced into the pens twice daily (10:00 a.m. and 2:30 p.m.) on days 0 through 6 and days 14 through 20. Pats were placed in the pen at random locations to mimic defecation of a steer within the pen. Fecal grab samples, hide swab samples (500-cm2 area of the rump), natural fecal pat samples (freshly voided), and rope samples (1.22-m-long manila rope) where obtained at multiple times during the 49-day trial to evaluate the spread of nalidixic acid-resistant E. coli O157:H7 throughout the feedlot environment and among penmates. Immunomagnetic separation and selective media were used to detect E. coli O157:H7. Nalidixic acid-resistant E. coli O157:H7 was detected in 13 high-level treatment fecal grab samples, 7 high-level treatment hide swab samples, 1 low-level hide swab sample, and 2 high-level rope samples. For both fecal grab and hide swab samples, the overall prevalence of E. coli O157:H7 in the high-level group was greater (P < 0.01) than that for the pooled low-level and control groups. Addition of inoculated fecal pats to pens increased transmission of E. coli O157:H7 among penmates, but cattle that acquired E. coli O157:H7 shed the bacterium for only a short time at low levels. Transmission of E. coli O157:H7 from the feces of super shedders to naive penmates may contribute to the observed transient nature of shedding of E. coli O157:H7 among feedlot cattle.

Multiple-locus variable number of tandem repeat analysis (MLVA) of Irish verocytotoxigenic Escherichia coli O157 from feedlot cattle: uncovering strain dissemination routes

BACKGROUND

The identification of the routes of dissemination of Escherichia coli (E. coli) O157 through a cohort of cattle is a critical step to control this pathogen at farm level. The aim of this study was to identify potential routes of dissemination of E. coli O157 using Multiple-Locus Variable number of tandem repeat Analysis (MLVA).

RESULTS

Thirty-eight environmental and sixteen cattle faecal isolates, which were detected in four adjacent pens over a four-month period were sub-typed. MLVA could separate these isolates into broadly defined clusters consisting of twelve MLVA types. Strain diversity was observed within pens, individual cattle and the environment.

CONCLUSION

Application of MLVA is a broadly useful and convenient tool when applied to uncover the dissemination of E. coli O157 in the environment and in supporting improved on-farm management of this important pathogen. These data identified diverse strain types based on amplification of VNTR markers in each case.

Transportation and lairage environment effects on prevalence, numbers, and diversity of Escherichia coli O157:H7 on hides and carcasses of beef cattle at processing

Hide has been established as the main source of carcass contamination during cattle processing; therefore, it is crucial to minimize the amount of Escherichia coli O157:H7 on cattle hides before slaughter. Several potential sources of E. coli O157: H7 are encountered during transportation and in the lairage environment at beef-processing facilities that could increase the prevalence and numbers of E. coli O157:H7 on the hides of cattle. On three separate occasions, samples were obtained from cattle at the feedlot and again after cattle were stunned and exsanguinated at the processing plant (286 total animals). The prevalence of E. coli O157:H7 on hides increased from 50.3 to 94.4% between the time cattle were loaded onto tractor-trailers at the feedlot and the time hides were removed in the processing plant. Before transport, nine animals had E. coli O157:H7 in high numbers (> 0.4 CFU/cm2) on their hides. When sampled at the slaughter facility, the number of animals with high hide numbers had increased to 70. Overall, only 29% of the E. coli O157:H7 isolates collected postharvest (221 of 764) matched pulsed-field gel electrophoresis types collected before transport. The results of this study indicate that transport to and lairage at processing plants can lead to increases in the prevalence and degree of E. coli O157:H7 contamination on hides and the number of E. coli O157:H7 pulsed-field gel electrophoresis types associated with the animals. More study is needed to confirm the mechanism by which additional E. coli O157:H7 strains contaminate cattle hides during transport and lairage and to design interventions to prevent this contamination.

Social and sexual behaviours aid transmission of bacteria in birds

Understanding the behavioural mechanisms that mediate pathogen transmission in social hosts like birds could provide the empirical bases for explaining the epidemiological dynamics of zoonotic infections in vertebrates. By experimentally infecting the feathers and cloaca of captive zebra finches (Taeniopygia guttata), with the bacterium Bacillus licheniformis PWD1 (BL), we examined the self-contamination and horizontal transmission of birds sharing the same environment. We also examined whether sexual transmission of bacteria is gender biased. Our results show that bacteria placed on the plumage of the birds lead to self and allo-infections of the bird guts, possibly through preening behaviours and bacterial ingestion. Furthermore, we found that sexual transmission of the bacteria was asymmetrical, being higher when males are the transmitting sex. Our results suggest the existence of an oral-faecal-genital route of bacterial transmission for avian hosts, wherein bacteria present on feathers infect their host guts through self and allo-preening and bacterial ingestion. Gut bacteria can then be transmitted sexually with transmission rate being higher when males are the infected sex.

A comparison of the survival in feces and water of Escherichia coli O157:H7 grown under laboratory conditions or obtained from cattle feces

Escherichia coli O157:H7 is an important foodborne pathogen that can cause hemorrhagic colitis and hemolytic uremic syndrome. Cattle feces and fecally contaminated water are important in the transmission of this organism on the farm. In this study, the survival of E. coli O157:H7 in feces and water was compared following passage through the animal digestive tract or preparation in the laboratory. Feces were collected from steers before and after oral inoculation with a marked strain of E. coli O157:H7. Fecal samples collected before cattle inoculation were subsequently inoculated with the marked strain of E. coli O157:H7 prepared in the laboratory. Subsamples were taken from both animal and laboratory-inoculated feces to inoculate 5-liter volumes of water. E. coli O157:H7 in feces survived up to 97 days, and survival was not affected by the method used to prepare the inoculating strain. E. coli O157:H7 survived up to 109 days in water, and the bacteria collected from inoculated cattle were detected up to 10 weeks longer than the laboratory-prepared culture. This study suggests that pathogen survival in low-nutrient conditions may be enhanced by passage through the gastrointestinal tract.