Are super-shedder feedlot cattle really super?

Super Shedding in Enteric Pathogens: A Review

Super shedding occurs when a small number of individuals from a given host population shed high levels of a pathogen. Beyond this general definition, various interpretations of the shedding patterns have been proposed to identify super shedders, leading to the description of the super shedding phenomenon in a wide range of pathogens, in particular enteric pathogens, which are of considerable interest. Several underlying mechanisms may explain this observation, including factors related to the environment, the gut microbiota, the pathogen itself (i.e., genetic polymorphism), and the host (including immune factors). Moreover, data suggest that the interplay of these parameters, in particular at the host-pathogen-gut microbiota interface, is of crucial importance for the determination of the super shedding phenotype in enteric pathogens. As a phenomenon playing an important role in the epidemics of enteric diseases, the evidence of super shedding has highlighted the need to develop various control strategies.

Transmission of antimicrobial resistance (AMR) during animal transport

The transmission of antimicrobial resistance (AMR) between food-producing animals (poultry, cattle and pigs) during short journeys (< 8 h) and long journeys (> 8 h) directed to other farms or to the slaughterhouse lairage (directly or with intermediate stops at assembly centres or control posts, mainly transported by road) was assessed. Among the identified risk factors contributing to the probability of transmission of antimicrobial-resistant bacteria (ARB) and antimicrobial resistance genes (ARGs), the ones considered more important are the resistance status (presence of ARB/ARGs) of the animals pre-transport, increased faecal shedding, hygiene of the areas and vehicles, exposure to other animals carrying and/or shedding ARB/ARGs (especially between animals of different AMR loads and/or ARB/ARG types), exposure to contaminated lairage areas and duration of transport. There are nevertheless no data whereby differences between journeys shorter or longer than 8 h can be assessed. Strategies that would reduce the probability of AMR transmission, for all animal categories include minimising the duration of transport, proper cleaning and disinfection, appropriate transport planning, organising the transport in relation to AMR criteria (transport logistics), improving animal health and welfare and/or biosecurity immediately prior to and during transport, ensuring the thermal comfort of the animals and animal segregation. Most of the aforementioned measures have similar validity if applied at lairage, assembly centres and control posts. Data gaps relating to the risk factors and the effectiveness of mitigation measures have been identified, with consequent research needs in both the short and longer term listed. Quantification of the impact of animal transportation compared to the contribution of other stages of the food-production chain, and the interplay of duration with all risk factors on the transmission of ARB/ARGs during transport and journey breaks, were identified as urgent research needs.

Persistent Circulation of Enterohemorrhagic Escherichia coli (EHEC) O157:H7 in Cattle Farms: Characterization of Enterohemorrhagic Escherichia coli O157:H7 Strains and Fecal Microbial Communities of Bovine Shedders and Non-shedders

Cattle are carriers, without clinical manifestations, of enterohemorrhagic Escherichia coli (EHEC) O157:H7 responsible for life-threatening infections in humans. A better identification of factors playing a role in maintaining persistence of such strains in cattle is required to develop more effective control measures. Hence, we conducted a study to identify farms with a persistent circulation of EHEC O157:H7. The EHEC O157:H7 herd status of 13 farms, which had previously provided bovine EHEC O157:H7 carriers at slaughter was investigated. Two farms were still housing positive young bulls, and this was true over a 1-year period. Only one fecal sample could be considered from a supershedder, and 60% of the carriers shed concentrations below 10 MPN/g. Moreover, EHEC O157:H7 represented minor subpopulations of E. coli. PFGE analysis of the EHEC O157:H7 strains showed that persistent circulation was due either to the persistence of a few predominant strains or to the repeated exposure of cattle to various strains. Finally, we compared fecal microbial communities of shedders (S) (n = 24) and non-shedders (NS) (n = 28), including 43 young bulls and nine cows, from one farm. Regarding alpha diversity, no significant difference between S vs. NS young bulls (n = 43) was observed. At the genus level, we identified 10 amplicon sequence variant (ASV) indicators of the S or NS groups. The bacterial indicators of S belonged to the family XIII UCG-001, Slackia, and Campylobacter genera, and Ruminococcaceae NK4A21A, Lachnospiraceae-UGC-010, and Lachnospiraceae-GCA-900066575 groups. The NS group indicator ASVs were affiliated to Pirellulaceae-1088-a5 gut group, Anaerovibrio, Victivallis, and Sellimonas genera. In conclusion, the characteristics enhancing the persistence of some predominant strains observed here should be explored further, and studies focused on mechanisms of competition among E. coli strains are also needed.

MicroRNAomes of Cattle Intestinal Tissues Revealed Possible miRNA Regulated Mechanisms Involved in Escherichia coli O157 Fecal Shedding

Cattle have been suggested as the primary reservoirs of E. coli O157 mainly as a result of colonization of the recto-anal junction (RAJ) and subsequent shedding into the environment. Although a recent study reported different gene expression at RAJ between super-shedders (SS) and non-shedders (NS), the regulatory mechanisms of altered gene expression is unknown. This study aimed to investigate whether bovine non-coding RNAs play a role in regulating the differentially expressed (DE) genes between SS and NS, thus further influencing E. coli O157 shedding behavior in the animals through studying miRNAomes of the whole gastrointestinal tract including duodenum, proximal jejunum, distal jejunum, cecum, spiral colon, descending colon and rectum. The number of miRNAs detected in each intestinal region ranged from 390 ± 13 (duodenum) to 413 ± 49 (descending colon). Comparison between SS and NS revealed the number of differentially expressed (DE) miRNAs ranged from one (in descending colon) to eight (in distal jejunum), and through the whole gut, seven miRNAs were up-regulated and seven were down-regulated in SS. The distal jejunum and rectum were the regions where the most DE miRNAs were identified (eight and seven, respectively). The miRNAs, bta-miR-378b, bta-miR-2284j, and bta-miR-2284d were down-regulated in both distal jejunum and rectum of SS (log₂fold-change: −2.7 to −3.8), bta-miR-2887 was down-regulated in the rectum of SS (log₂fold-change: −3.2), and bta-miR-211 and bta-miR-29d-3p were up-regulated in the rectum of SS (log₂fold-change: 4.5 and 2.2). Functional analysis of these miRNAs indicated their potential regulatory role in host immune functions, including hematological system development and immune cell trafficking. Our findings suggest that altered expression of miRNA in the gut of SS may lead to differential regulation of immune functions involved in E. coli O157 super-shedding in cattle.

Effectiveness of a Direct-Fed Microbial Product Containing Lactobacillus acidophilus and Lactobacillus casei in Reducing Fecal Shedding of Escherichia coli O157:H7 in Commercial Feedlot Cattle

The objective of this study was to evaluate the effectiveness of a direct-fed microbial (DFM) product in reducing fecal shedding of Escherichia coli O157:H7 in finishing commercial feedlot cattle in Kansas (KS) and Nebraska (NE). Utilizing a randomized complete block design within the feedlot (KS, n = 1; NE, n = 1), cattle were randomly allocated to 20 pens, grouped in blocks of two based on allocation date, and then, within the block, randomly assigned to a treatment group (DFM or negative control). The DFM product was included in the diet at a targeted daily dose of 1 × 10⁹ colony-forming units (CFU) of the Lactobacillus acidophilus and Lactobacillus casei combination per animal for at least 60 d before sampling. Feedlots were sampled for four consecutive weeks; weekly sampling consisted of collecting 20 pen floor fecal samples per pen. Fecal samples were subjected to culture-based methods for detection and isolation of E. coli O157, and positive samples were quantified using real-time polymerase chain reaction. Primary outcomes of interest were fecal prevalence of E. coli O157:H7 and E. coli O157 supershedding (≥10⁴ CFU/g of feces) prevalence. Data for each feedlot were analyzed at the pen level using mixed models accounting for the study design features. Model-adjusted mean E. coli O157:H7 fecal prevalence estimates (standard error of the mean [SEM]) for DFM and control groups were 8.2% (SEM = 2.2%) and 9.9% (SEM = 2.5%) in KS and 14.6% (SEM = 2.8%) versus 14.3% (SEM = 2.6%) in NE; prevalence did not differ significantly between treatment groups at either site (KS, p = 0.51; NE, p = 0.92). Mean E. coli O157 supershedding prevalence estimates for DFM and control groups were 2.2% (SEM = 0.7%) versus 1.8% (SEM = 0.7%) in KS (p = 0.66) and 6.7% (SEM = 1.5%) versus 3.2% (SEM = 1.0%) in NE (p = 0.04). In conclusion, administering the DFM product in the finishing diet of feedlot cattle did not significantly reduce E. coli O157:H7 fecal prevalence or supershedding prevalence in study pens at either commercial feedlot.

Precision public health to inhibit the contagion of disease and move toward a future in which microbes spread health

Antimicrobial resistance continues to outpace the development of new chemotherapeutics. Novel pathogens continue to evolve and emerge. Public health innovation has the potential to open a new front in the war of "our wits against their genes" (Joshua Lederberg). Dense sampling coupled to next generation sequencing can increase the spatial and temporal resolution of microbial characterization while sensor technologies precisely map physical parameters relevant to microbial survival and spread. Microbial, physical, and epidemiological big data could be combined to improve prospective risk identification. However, applied in the wrong way, these approaches may not realize their maximum potential benefits and could even do harm. Minimizing microbial-human interactions would be a mistake. There is evidence that microbes previously thought of at best "benign" may actually enhance human health. Benign and health-promoting microbiomes may, or may not, spread via mechanisms similar to pathogens. Infectious vaccines are approaching readiness to make enhanced contributions to herd immunity. The rigorously defined nature of infectious vaccines contrasts with indigenous "benign or health-promoting microbiomes" but they may converge. A "microbial Neolithic revolution" is a possible future in which human microbial-associations are understood and managed analogously to the macro-agriculture of plants and animals. Tradeoffs need to be framed in order to understand health-promoting potentials of benign, and/or health-promoting microbiomes and infectious vaccines while also discouraging pathogens. Super-spreaders are currently defined as individuals who play an outsized role in the contagion of infectious disease. A key unanswered question is whether the super-spreader concept may apply similarly to health-promoting microbes. The complex interactions of individual rights, community health, pathogen contagion, the spread of benign, and of health-promoting microbiomes including infectious vaccines require study. Advancing the detailed understanding of heterogeneity in microbial spread is very likely to yield important insights relevant to public health.

Petting zoos as sources of Shiga toxin-producing Escherichia coli (STEC) infections

Despite their general low incidence, Shiga toxin-producing Escherichia (E.) coli (STEC) infections are considered an important public health issue due to the severity of illness that can develop, particularly in young children. We report on two Austrian petting zoos, one in Tyrol (2015) and one in Vorarlberg (2016), which were identified as highly likely infection sources of STEC infections. The petting zoo related cases involved a case of hemolytic uremic syndrome (HUS) due to STEC O157:HNM in 2015 and an outbreak of STEC O157:H7 infections affecting five young children and two adults in 2016. The HUS case accounted for 2.8% of the 36 STEC O157:HNM/H7 infections notified in Austria in 2015 (5,9% of 17 HUS cases). The seven cases described for 2016 accounted for 4.0% of the 177 human STEC infections documented for Austria in 2016, and for 19.4% of the 36 STEC O157:HNM/H7 infections notified that year. The evaluation of the STEC infections described here clearly underlines the potential of sequence-based typing methods to offer suitable resolutions for public health applications. Furthermore, we give a state-of-the-art mini-review on the risks of petting zoos concerning exposure to the zoonotic hazard STEC and on proper measures of risk-prevention.

Quantitative surveillance of shiga toxins 1 and 2, Escherichia coli O178 and O157 in feces of western-Canadian slaughter cattle enumerated by droplet digital PCR with a focus on seasonality and slaughterhouse location

Often Escherichia coli are harmless and/or beneficial bacteria inhabiting the gastrointestinal tract of livestock and humans. However, Shiga toxin-producing E. coli (STEC) have been linked to human disease. Cattle are the primary reservoir for STEC and STEC “super-shedders” are considered to be a major contributor in animal to animal transmission. Among STEC, O157:H7 is the most recognized serotype, but in recent years, non-O157 STEC have been increasingly linked to human disease. In Argentina and Germany, O178 is considered an emerging pathogen. Our objective was to compare populations of E. coli O178, O157, shiga toxin 1 and 2 in western Canadian cattle feces from a sampling pool of ~80,000 beef cattle collected at two slaughterhouses. Conventional PCR was utilized to screen 1,773 samples for presence/absence of E. coli O178. A subset of samples (n = 168) was enumerated using droplet digital PCR (ddPCR) and proportions of O178, O157 and shiga toxins 1 & 2 specific-fragments were calculated as a proportion of generic E. coli (GEC) specific-fragments. Distribution of stx₁ and stx₂ was determined by comparing stx₁, stx₂ and O157 enumerations. Conventional PCR detected the presence of O178 in 873 of 1,773 samples and ddPCR found the average proportion of O178, O157, stx₁ and stx₂ in the samples 2.8%, 0.6%, 1.4% and 0.5%, respectively. Quantification of stx₁ and stx₂ revealed more virulence genes than could be exclusively attributed to O157. Our results confirmed the presence of E. coli O178 in western Canadian cattle and ddPCR revealed O178 as a greater proportion of GEC than was O157. Our results suggests: I) O178 may be an emerging subgroup in Canada and II) monitoring virulence genes may be a more relevant target for food-safety STEC surveillance compared to current serogroup screening.

Interactions of the Hindgut Mucosa-Associated Microbiome with Its Host Regulate Shedding of Escherichia coli O157:H7 by Cattle

Cattle are the primary carrier of Escherichia coli O157:H7, a foodborne human pathogen, and those shedding >10⁴ CFU/gram of feces of E. coli O157:H7 are defined as supershedders (SS). This study investigated the rectoanal junction (RAJ) mucosa-associated microbiota and its relationship with host gene expression in SS and in cattle from which E. coli O157:H7 was not detected (nonshedders [NS]), aiming to elucidate the mechanisms involved in supershedding. In total, 14 phyla, 66 families, and 101 genera of RAJ mucosa-associated bacteria were identified and Firmicutes (61.5 ± 7.5%), Bacteroidetes (27.9 ± 6.4%), and Proteobacteria (5.5 ± 2.1%) were the predominant phyla. Differential abundance analysis of operational taxonomic units (OTUs) identified 2 OTUs unique to SS which were members of Bacteroides and Clostridium and 7 OTUs unique to NS which were members of Coprococcus, Prevotella, Clostridium, and Paludibacter Differential abundance analysis of predicted microbial functions (using PICRUSt [phylogenetic investigation of communities by reconstruction of unobserved states]) revealed that 3 pathways had higher abundance (log₂ fold change, 0.10 to 0.23) whereas 12 pathways had lower abundance (log₂ fold change, -0.36 to -0.20) in SS. In addition, we identified significant correlations between expression of 19 differentially expressed genes and the relative abundance of predicted microbial functions, including nucleic acid polymerization and carbohydrate and amino acid metabolism. Our findings suggest that differences in RAJ microbiota at both the compositional and functional levels may be associated with E. coli O157:H7 supershedding and that certain microbial groups and microbial functions may influence RAJ physiology of SS by affecting host gene expression.IMPORTANCE Cattle with fecal E. coli O157:H7 at >10⁴ CFU per gram of feces have been defined as the supershedders, and they are responsible for the most of the E. coli O157:H7 spread into farm environment. Currently, no method is available for beef producers to eliminate shedding of E. coli O157:H7 in cattle, and the lack of information about the mechanisms of supershedding greatly impedes the development of effective methods. This study investigated the role of the rectoanal junction (RAJ) mucosa-associated microbiome in E. coli O157:H7 shedding, and our results indicated that the compositions and functions of RAJ microbiota differed between supershedders and nonshedders. The identified relationship between the differentially abundant microbes and 19 previously identified differentially expressed genes suggests the role of host-microbial interactions involved in E. coli O157:H7 supershedding. Our findings provide a fundamental understanding of the supershedding phenomenon which is essential for the development of strategies, such as the use of directly fed microbials, to reduce E. coli O157:H7 shedding in cattle.

Host mechanisms involved in cattle Escherichia coli O157 shedding: a fundamental understanding for reducing foodborne pathogen in food animal production

The host mechanisms involved in Escherichia coli O157 super-shedding in cattle is largely unknown. In this study, the comparison of transcriptomes of intestinal tissues between super-shedders (SS) and cattle negative for E. coli O157 (NS) was performed, aiming to identify genes that are potentially associated with super-shedding. In total, 16,846 ± 639 (cecum) to 18,137 ± 696 (distal jejunum) were expressed throughout the intestine, with the expressed genes associated with immune functions more pronounced in the small intestine. In total, 351 differentially expressed (DE) genes were identified throughout the intestine between SS and NS, with 101 being up-regulated and 250 down-regulated in SS. Functional analysis revealed DE genes were involved in increased T-cell responses and cholesterol absorption in the distal jejunum and descending colon, and decreased B-cell maturation in the distal jejunum of SS. RNA-Seq based SNP discovery revealed that the mutations in seven DE genes involved in leukocyte activation and cholesterol transportation were associated with E. coli O157 shedding. Our findings suggest that T-cell responses and cholesterol metabolism in the intestinal tract may be associated with super-shedding phenomenon, and the SNPs in the DE genes are possibly associated with the observed gene expression difference between SS and NS.

Changes in bacterial community composition of Escherichia coli O157:H7 super-shedder cattle occur in the lower intestine

Escherichia coli O157:H7 is a foodborne pathogen that colonizes ruminants. Cattle are considered the primary reservoir of E. coli O157:H7 with super-shedders, defined as individuals excreting > 10⁴E. coli O157:H7 CFU g^-1 feces. The mechanisms leading to the super-shedding condition are largely unknown. Here, we used 16S rRNA gene pyrosequencing to examine the composition of the fecal bacterial community in order to investigate changes in the bacterial microbiota at several locations along the digestive tract (from the duodenum to the rectal-anal junction) in 5 steers previously identified as super-shedders and 5 non-shedders. The overall bacterial community structure did not differ by E. coli O157:H7 shedding status; but several differences in the relative abundance of taxa and OTUs were noted between the two groups. The genus Prevotella was most enriched in the non-shedders while the genus Ruminococcus and the Bacteroidetes phylum were notably enriched in the super-shedders. There was greater bacterial diversity and richness in samples collected from the lower- as compared to the upper gastrointestinal tract (GI). The spiral colon was the only GI location that differed in terms of bacterial diversity between super-shedders and non-shedders. These findings reinforced linkages between E. coli O157:H7 colonization in cattle and the nature of the microbial community inhabiting the digestive tract of super-shedders.

Daily shedding dynamics of E. coli O157 in an Australian grass-fed beef herd

This study aimed to describe the diurnal shedding dynamics of Escherichia coli O157 in cattle managed on pasture. The purpose was to identify the value of a single measurement for predicting the shedding status on subsequent days. Over a 14-day period, 24 beef cows with known E. coli O157 shedding status were sampled twice daily or daily (21 sampling points) and E. coli O157 was enumerated from faeces. No association between shedding status of individual animals within a 7-h period was identified (odds ratio 1·5, P = 0·08). Short-interval sampling demonstrated substantial diurnal volatility in shedding of E. coli O157 that is not evident in studies based on long-interval (>7 days) sampling. The findings contribute to and support previous findings on the question why it has been difficult to achieve progress in understanding the epidemiology of E. coli O157 infection in cattle.

Comparative Genomic Analysis of Escherichia coli O157:H7 Isolated from Super-Shedder and Low-Shedder Cattle

Cattle are the primary reservoir of the foodborne pathogen Escherichia coli O157:H7, with the concentration and frequency of E. coli O157:H7 shedding varying substantially among individual hosts. The term ''super-shedder" has been applied to cattle that shed ≥10(4) cfu E. coli O157:H7/g of feces. Super-shedders have been reported to be responsible for the majority of E. coli O157:H7 shed into the environment. The objective of this study was to determine if there are phenotypic and/or genotypic differences between E. coli O157:H7 isolates obtained from super-shedder compared to low-shedder cattle. From a total of 784 isolates, four were selected from low-shedder steers and six isolates from super-shedder steers (4.01-8.45 log cfu/g feces) for whole genome sequencing. Isolates were phage and clade typed, screened for substrate utilization, pH sensitivity, virulence gene profiles and Stx bacteriophage insertion (SBI) sites. A range of 89-2473 total single nucleotide polymorphisms (SNPs) were identified when sequenced strains were compared to E. coli O157:H7 strain Sakai. More non-synonymous SNP mutations were observed in low-shedder isolates. Pan-genomic and SNPs comparisons did not identify genetic segregation between super-shedder or low-shedder isolates. All super-shedder isolates and 3 of 4 of low-shedder isolates were typed as phage type 14a, SBI cluster 3 and SNP clade 2. Super-shedder isolates displayed increased utilization of galactitol, thymidine and 3-O-β-D-galactopyranosyl-D-arabinose when compared to low-shedder isolates, but no differences in SNPs were observed in genes encoding for proteins involved in the metabolism of these substrates. While genetic traits specific to super-shedder isolates were not identified in this study, differences in the level of gene expression or genes of unknown function may still contribute to some strains of E. coli O157:H7 reaching high densities within bovine feces.

Comparative Transcriptomic Analysis of Rectal Tissue from Beef Steers Revealed Reduced Host Immunity in Escherichia coli O157:H7 Super-Shedders

Super-shedder cattle are a major disseminator of E. coli O157:H7 into the environment, and the terminal rectum has been proposed as the primary E. coli O157:H7 colonization site. This study aimed to identify host factors that are associated with the super-shedding process by comparing transcriptomic profiles in rectal tissue collected from 5 super-shedder cattle and 4 non-shedder cattle using RNA-Seq. In total, 17,859 ± 354 genes and 399 ± 16 miRNAs were detected, and 11,773 genes were expressed in all animals. Fifty-eight differentially expressed (DE) genes (false discovery rate < 0.05) including 11 up-regulated and 47 down-regulated (log 2 (fold change) ranged from -5.5 to 4.2), and 2 up-regulated DE miRNAs (log 2 (fold change) = 2.1 and 2.5, respectively) were identified in super-shedders compared to non-shedders. Functional analysis of DE genes revealed that 31 down-regulated genes were potentially associated with reduced innate and adaptive immune functions in super-shedders, including 13 lymphocytes membrane receptors, 3 transcription factors and 5 cytokines, suggesting the decreased key host immune functions in the rectal tissue of super-shedders, including decreased quantity and migration of immune cells such as lymphocytes, neutrophils and dendritic cells. The up-regulation of bta-miR-29d-3p and the down regulation of its predicted target gene, regulator of G-protein signaling 13, suggested a potential regulatory role of this miRNA in decreased migration of lymphocytes in super-shedders. Based on these findings, the rectal tissue of super-shedders may inherently exhibit less effective innate and adaptive immune protection. Further study is required to confirm if such effect on host immunity is due to the nature of the host itself or due to actions mediated by E. coli O157:H7.

Longitudinal study of Escherichia coli O157 shedding and super shedding in dairy heifers

A longitudinal study was conducted to assess the methods available for detection of Escherichia coli O157 and to investigate the prevalence and occurrence of long-term shedding and super shedding in a cohort of Australian dairy heifers. Samples were obtained at approximately weekly intervals from heifers at pasture under normal management systems. Selective sampling techniques were used with the aim of identifying heifers with a higher probability of shedding or super shedding. Rectoanal mucosal swabs (RAMS) and fecal samples were obtained from each heifer. Direct culture of feces was used for detection and enumeration. Feces and RAMS were tested by enrichment culture. Selected samples were further tested retrospectively by immunomagnetic separation of enriched samples. Of 784 samples obtained, 154 (19.6%) were detected as positive using culture methods. Adjusting for selective sampling, the prevalence was 71 (15.6%) of 454. In total, 66 samples were detected as positive at >10(2) CFU/g of which 8 were >10(4) CFU/g and classed as super shedding. A significant difference was observed in detection by enriched culture of RAMS and feces. Dairy heifers within this cohort exhibited variable E. coli O157 shedding, consistent with previous estimates of shedding. Super shedding was detected at a low frequency and inconsistently from individual heifers. All detection methods identified some samples as positive that were not detected by any other method, indicating that the testing methods used will influence survey results.

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.

Daily variations in Escherichia coli O157 shedding patterns in a cohort of dairy heifers at pasture

Escherichia coli O157 is a human pathogen carried asymptomatically by cattle and shed in their faeces. Infection can occur from the consumption of contaminated beef or by direct contact. Large variations of E. coli O157 shedding in cattle exist and vary in the number of cattle positive for E. coli O157 and the amount of bacteria (c.f.u./g faeces) shed by positive animals. To investigate E. coli O157 shedding and super-shedding (>104 c.f.u./g) we used daily sampling over two 8-day periods; in January 2013 (n = 12) and February 2013 (n = 21). Samples were tested by direct faecal culture for enumeration and by immunomagnetic separation to detect lower levels of shedding. We identified three patterns of shedding, similar to previously observed descriptions: intermittent, transient and consistent. The most commonly observed pattern was intermittent shedding and variation in the level of shedding could be large. This extreme variation is demonstrated by a heifer from which E. coli O157 could be not detected one day, was super-shedding E. coli O157 the next and was detected as shedding >100 c.f.u./g the following day. Recto-anal mucosal swab testing did not predict super-shedding in this cohort of heifers. The variable individual patterns of shedding suggest that a common mechanism of infection may not operate within such a herd when considering previously described patterns and the inferred mechanisms. The sporadic and intermittent nature of shedding is a challenge to identifying risk factors and potential intervention strategies.

Differing populations of endemic bacteriophages in cattle shedding high and low numbers of Escherichia coli O157:H7 bacteria in feces

The objectives of this study were to identify endemic bacteriophages (phages) in the feedlot environment and determine relationships of these phages to Escherichia coli O157:H7 from cattle shedding high and low numbers of naturally occurring E. coli O157:H7. Angus crossbred steers were purchased from a southern Alberta (Canada) feedlot where cattle excreting ≥ 10(4) CFU · g(-1) of E. coli O157:H7 in feces at a single time point were identified as supershedders (SS; n = 6), and cattle excreting <10(4) CFU · g(-1) of feces were identified as low shedders (LS; n = 5). Fecal pats or fecal grabs were collected daily from individual cattle for 5 weeks. E. coli O157:H7 in feces was detected by immunomagnetic separation and enumerated by direct plating, and phages were isolated using short- and overnight-enrichment methods. The total prevalence of E. coli O157:H7 isolated from feces was 14.4% and did not differ between LS and SS (P = 0.972). The total prevalence of phages was higher in the LS group (20.9%) than in the SS group (8.3%; P = 0.01). Based on genome size estimated by pulsed-field gel electrophoresis and morphology determined by transmission electron microscopy, T4- and O1-like phages of Myoviridae and T1-like phage of Siphoviridae were isolated. Compared to T1- and O1-like phages, T4-like phages exhibited a broad host range and strong lytic capability when targeting E. coli O157:H7. Moreover, the T4-like phages were more frequently isolated from feces of LS than SS, suggesting that endemic phages may impact the shedding dynamics of E. coli O157:H7 in cattle.