Carriage and Subtypes of Foodborne Pathogens Identified in Wild Birds Residing near Agricultural Lands in California: a Repeated Cross-Sectional Study

From field to plate: How do bacterial enteric pathogens interact with ready-to-eat fruit and vegetables, causing disease outbreaks?

Ready-to-eat fruit and vegetables are a convenient source of nutrients and fibre for consumers, and are generally safe to eat, but are vulnerable to contamination with human enteric bacterial pathogens. Over the last decade, Salmonella spp., pathogenic Escherichia coli, and Listeria monocytogenes have been linked to most of the bacterial outbreaks of foodborne illness associated with fresh produce. The origins of these outbreaks have been traced to multiple sources of contamination from pre-harvest (soil, seeds, irrigation water, domestic and wild animal faecal matter) or post-harvest operations (storage, preparation and packaging). These pathogens have developed multiple processes for successful attachment, survival and colonization conferring them the ability to adapt to multiple environments. However, these processes differ across bacterial strains from the same species, and across different plant species or cultivars. In a competitive environment, additional risk factors are the plant microbiome phyllosphere and the plant responses; both factors directly modulate the survival of the pathogens on the leaf's surface. Understanding the mechanisms involved in bacterial attachment to, colonization of, and proliferation, on fresh produce and the role of the plant in resisting bacterial contamination is therefore crucial to reducing future outbreaks.

Circulation of Antibiotic-Resistant Escherichia coli in Wild and Domestic Waterfowl in Ukraine

Background: Antibiotic resistance is becoming an increasingly urgent problem for human and animal health due to the widespread use of antibiotics in medicine, veterinary medicine, and agriculture. At the same time, the natural reservoirs of antibiotic-resistant pathogens remain unclear. Wild birds may play a role in this due to their biology. Escherichia coli is a representative indicator pathogen for antibiotic resistance studies. Materials and Methods: In 2020-2021, sampling of feces and cloacal swabs from six species of wild waterfowl (Eurasian wigeon Anas penelope, Eurasian teal Anas crecca, white-fronted goose Anser albifrons, red-breasted goose Rufibrenta ruficollis, graylag goose Anser anser, shelduck Tadorna tadorna) and from two species of domestic waterfowl (ducks and geese) was conducted in the Kherson, Zaporizhzhia, Odesa, Kharkiv, and Cherkasy regions of Ukraine. Biological material was collected, stored, and transported in cryotubes with transport medium (brain heart infusion broth [BHIB] with the addition of 15% glycerol) in liquid nitrogen. Bacteriological studies were carried out according to standard methods for the isolation and identification of microorganisms. Drug resistance of E. coli was carried out by a standard disk diffusion method. Results: Bacteria representing six families (Enterobacteriaceae, Yersiniaceae, Morganellaceae, Bacillaceae, Pseudomonadaceae, Staphylococcaceae) were isolated from clinically healthy wild birds (wigeon, Eurasian teal, white-fronted goose, red-breasted goose, mallard, graylag goose, shelduck) in the southern regions of Ukraine with isolation rates ranging from 26.7% to 100%. A total of 19 E. coli isolates were cultured from 111 samples from wild birds, and 30 isolates of E. coli were cultured from 32 poultry samples. E. coli was isolated from birds of all species. The prevalence of E. coli ranged from 5.0% to 33.3% in wild waterfowl and from 90.9% to 100% in domestic waterfowl. The prevalence of multidrug-resistant (MDR) E. coli ranged from 10.0% to 31.8% in wild and domestic waterfowl: 3 of 15 (20%) specimens from wild mallard were MDR in the Kherson region, as well as 7 of 22 domestic ducks (31.8%) and 1 of 10 geese (10%) in the Kharkiv and Cherkasy regions. Isolates from wild birds were the most resistant to ampicillin (AMP), amoxiclav (AMC), amoxicillin (AMX), doxycycline (DO), and chloramphenicol (C). Isolates from poultry were resistant to ampicillin, amoxiclav, doxycycline, amoxicillin, chloramphenicol, and enrofloxacin (EX). Most of the other E. coli isolates from wild waterfowl were classified as non-multidrug-resistant (non-MDR) forms. Analysis of antibiotic sensitivity phenotypes showed that only four antibiotic-resistant phenotypes were detected among non-MDR bacteria, whereas among the MDR bacteria, two antibiotic-resistant phenotypes were detected in mallards and six in domestic waterfowl. Conclusion: The results of this study showed that wild waterfowl in Ukraine, which live in natural conditions and do not receive any antimicrobial drugs, are carriers of E. coli that are resistant to a number of antibiotics that are actively used in industrial poultry.

Prevalence and molecular characterization of Salmonella isolated from wild birds in fresh produce environments

Wild birds pose a difficult food safety risk to manage because they can avoid traditional wildlife mitigation strategies, such as fences. Birds often use agricultural fields and structures as foraging and nesting areas, which can lead to defecation on crops and subsequent transfer of foodborne pathogens. To assess the food safety risk associated with these events, wild bird feces were collected from produce fields across the southeastern United States during the 2021 and 2022 growing seasons. In total 773 fecal samples were collected from 45 farms across Florida, Georgia, South Carolina, and Tennessee, and 2.1% (n = 16) of samples were Salmonella-positive. Importantly, 75% of Salmonella were isolated from moist feces, showing reduced Salmonella viability when feces dry out. 16S microbiome analysis showed that presence of culturable Salmonella in moist feces correlated to a higher proportion of the Enterobacteriaceae family. From the Salmonella-positive samples, 62.5% (10/16) contained multi-serovar Salmonella populations. Overall, 13 serovars were detected, including six most commonly attributed to human illness (Enteriditis, Newport, Typhimurium, Infantis, Saintpaul, and Muenchen). PCR screening identified an additional 59 Salmonella-positive fecal samples, which were distributed across moist (n = 44) and dried feces (n = 15). On-farm point counts and molecular identification from fecal samples identified 57 bird species, including for 10 Salmonella-positive fecal samples. Overall, there was a low prevalence of Salmonella in fecal samples, especially in dried feces, and we found no evidence of Salmonella transmission to proximal foliage or produce. Fecal samples collected in farms close together shared highly related isolates by whole genome sequencing and also had highly similar Salmonella populations with comparable relative frequencies of the same serovars, suggesting the birds acquired Salmonella from a common source.

Pathogenicity assessment of Shiga toxin-producing Escherichia coli strains isolated from wild birds in a major agricultural region in California

Shiga toxin-producing Escherichia coli (STEC) consists of diverse strains differing in genetic make-up and virulence potential. To better understand the pathogenicity potential of STEC carried by the wildlife, three STEC and one E. coli strains isolated from wild birds near a major agricultural region in California were selected for comparative pathogenomic analyses. Three American crow (Corvus brachyrhynchos) strains, RM9088, RM9513, and RM10410, belonging to phylogroup A with serotypes O109:H48, O9:H30, and O113:H4, respectively, and a red-winged blackbird (Agelaius phoeniceus) strain RM14516 in phylogroup D with serotype O17:H18, were examined. Shiga toxin genes were identified in RM9088 (stx1a), RM10410 (stx1a + stx2d), and RM14516 (stx2a). Unlike STEC O157:H7 strain EDL933, none of the avian STEC strains harbored the pathogenicity islands OI-122, OI-57, and the locus of enterocyte effacement, therefore the type III secretion system biogenesis genes and related effector genes were absent in the three avian STEC genomes. Interestingly, all avian STEC strains exhibited greater (RM9088 and RM14516) or comparable (RM10410) cytotoxicity levels compared with EDL933. Comparative pathogenomic analyses revealed that RM9088 harbored numerous genes encoding toxins, toxins delivery systems, and adherence factors, including heat-labile enterotoxin, serine protease autotransporter toxin Pic, type VI secretion systems, protein adhesin Paa, fimbrial adhesin K88, and colonization factor antigen I. RM9088 also harbored a 36-Kb high pathogenicity island, which is related to iron acquisition and pathogenicity in Yersinia spp. Strain RM14516 carried an acid fitness island like the one in EDL933, containing a nine gene cluster involved in iron acquisition. Genes encoding extracellular serine protease EspP, subtilase cytotoxin, F1C fimbriae, and inverse autotransporter adhesin IatC were only detected in RM14516, and genes encoding serine protease autotransporter EspI and P fimbriae were only identified in RM10410. Although all curli genes were present in avian STEC strains, production of curli fimbriae was only detected for RM9088 and RM14516. Consistently, strong, moderate, and little biofilms were observed for RM9088, RM14516, and RM10410, respectively. Our study revealed novel combinations of virulence factors in two avian strains, which exhibited high level of cytotoxicity and strong biofilm formation. Comparative pathogenomics is powerful in assessing pathogenicity and health risk of STEC strains.

Monitoring the genetic variation of some Escherichia coli strains in wild birds and cattle

To date, there is limited data about the genetic relationship of Escherichia coli between wild birds and cattle because these birds act as silent vectors for many zoonotic bacteria. This study aimed to elucidate the role of rooming wild birds in the vicinity of cattle farm in transmission of the same pathogenic E. coli variants, identifying their virulence, resistance traits and genetic similarities of fimH virulence gene. About 240 faecal/cloacal swabs were collected from both species and examined bacteriologically. Escherichia coli was yielded in 45.8% and 32.5%, respectively, of examined cattle and wild birds. The most prevalent detected E. coli serovar was O26. High tetracycline and chloramphenicol resistance were recorded; however, gentamycin and ciprofloxacin exhibited the highest sensitivity rates. Polymerase chain reaction (PCR) conserved genotypic resistance (tetA and blaCTX-M) and virulence attributes (fimH, stx1, eaeA and ompA) of E. coli isolates were discussed in detail. The fimH gene revealed 100% sequence similarity when comparing with different E. coli isolates globally and locally. Finally, a close genetic association of E. coli with both wild birds and cattle was detected, thus strengthening its role in the dissemination of the infection via environment. Prevention and conservative policy should be carried as E. coli constitute enormous significant zoonotic risks to livestock and animal workers. Also, further studies to the whole genome sequencing of fimH, other virulence and resistance genes of E. coli are recommended trying to limit the possibilities of co-infection and transfer among different species.Contribution: The current study recorded updated data about the critical infectious role of wild birds to livestock, including cattle farms in Egypt. It also delivered some recommendations for good hygienic practices in cattle farms which must be implemented for handling animal manure.

Risk factors associated with the prevalence of Shiga-toxin-producing Escherichia coli in manured soils on certified organic farms in four regions of the USA

Introduction

Biological soil amendments of animal origin (BSAAO), including untreated amendments are often used to improve soil fertility and are particularly important in organic agriculture. However, application of untreated manure on cropland can potentially introduce foodborne pathogens into the soil and onto produce. Certified organic farms follow the USDA National Organic Program (NOP) standards that stipulate a 90- or 120-day interval between application of untreated manure and crop harvest, depending on whether the edible portion of the crop directly contacts the soil. This time-interval metric is based on environmental factors and does not consider a multitude of factors that might affect the survival of the main pathogens of concern. The objective of this study was to assess predictors for the prevalence of Shiga-toxin-producing Escherichia coli (non-O157 STEC) in soils amended with untreated manure on USDA-NOP certified farms.

Methods

A longitudinal, multi-regional study was conducted on 19 farms in four USA regions for two growing seasons (2017–2018). Untreated manure (cattle, horse, and poultry), soil, and irrigation water samples were collected and enrichment cultured for non-O157 STEC. Mixed effects logistic regression models were used to analyze the predictors of non-O157 STEC in the soil up to 180 days post-manure application.

Results and discussion

Results show that farm management practices (previous use with livestock, presence of animal feces on the field, season of manure application) and soil characteristics (presence of generic E. coli in the soil, soil moisture, sodium) increased the odds of STEC-positive soil samples. Manure application method and snowfall decreased the odds of detecting STEC in the soil. Time-variant predictors (year and sampling day) affected the presence of STEC. This study shows that a single metric, such as the time interval between application of untreated manure and crop harvest, may not be sufficient to reduce the food safety risks from untreated manure, and additional environmental and farm-management practices should also be considered. These findings are of particular importance because they provide multi-regional baseline data relating to current NOP wait-time standards. They can therefore contribute to the development of strategies to reduce pathogen persistence that may contribute to contamination of fresh produce typically eaten raw from NOP-certified farms using untreated manure.

Structural Equation Models Suggest That On-Farm Noncrop Vegetation Removal Is Not Associated with Improved Food Safety Outcomes but Is Linked to Impaired Water Quality

While growers have reported pressures to minimize wildlife intrusion into produce fields through noncrop vegetation (NCV) removal, NCV provides key ecosystem services. To model food safety and environmental tradeoffs associated with NCV removal, published and publicly available food safety and water quality data from the Northeastern United States were obtained. Because data on NCV removal are not widely available, forest-wetland cover was used as a proxy, consistent with previous studies. Structural equation models (SEMs) were used to quantify the effect of forest-wetland cover on (i) food safety outcomes (e.g., detecting pathogens in soil) and (ii) water quality (e.g., nutrient levels). Based on the SEMs, NCV was not associated with or had a protective effect on food safety outcomes (more NCV was associated with a reduced likelihood of pathogen detection). The probabilities of detecting Listeria spp. in soil (effect estimate [EE] = -0.17; P = 0.005) and enterohemorrhagic Escherichia coli in stream samples (EE = -0.27; P < 0.001) were negatively associated with the amount of NCV surrounding the sampling site. Larger amounts of NCV were also associated with lower nutrient, salinity, and sediment levels, and higher dissolved oxygen levels. Total phosphorous levels were negatively associated with the amount of NCV in the upstream watershed (EE = -0.27; P < 0.001). Similar negative associations (P < 0.05) were observed for other physicochemical parameters, such as nitrate (EE = -0.38). Our findings suggest that NCV should not be considered an inherent produce safety risk or result in farm audit demerits. This study also provides a framework for evaluating environmental tradeoffs associated with using specific preharvest food safety strategies. IMPORTANCE Currently, on-farm food safety decisions are typically made independently of conservation considerations, often with detrimental impacts on agroecosystems. Comanaging agricultural environments to simultaneously meet conservation and food safety aims is complicated because farms are closely linked to surrounding environments, and management decisions can have unexpected environmental, economic, and food safety consequences. Thus, there is a need for research on the conservation and food safety tradeoffs associated with implementing specific preharvest food safety practices. Understanding these tradeoffs is critical for developing adaptive comanagement strategies and ensuring the short- and long-term safety, sustainability, and profitability of agricultural systems. This study quantifies tradeoffs and synergies between food safety and environmental aims, and outlines a framework for modeling tradeoffs and synergies between management aims that can be used to support future comanagement research.

Risk factors of Shiga toxin-producing Escherichia coli in livestock raised on diversified small-scale farms in California

The increasing number of diversified small-scale farms (DSSF) that raise outdoor-based livestock in the USA reflects growing consumer demand for sustainably produced food. Diversified farms are small scale and raise a combination of multiple livestock species and numerous produce varieties. This 2015–2016 cross-sectional study aimed to describe the unique characteristics of DSSF in California, estimate the prevalence of Shiga toxin-producing Escherichia coli (STEC) in livestock and evaluate the association between risk factors and the presence of STEC in livestock, using generalised linear mixed models. STEC prevalence was 13.62% (76/558). Significant variables in the mixed-effect logistic regression model included daily maximum temperature (OR 0.95; CI_95% 0.91–0.98), livestock sample source (cattle (OR 4.61; CI_95% 1.64–12.96) and sheep (OR 5.29; CI_95% 1.80–15.51)), multiple species sharing the same barn (OR 6.23; CI_95% 1.84–21.15) and livestock having contact with wild areas (OR 3.63; CI_95% 1.37–9.62). Identification of STEC serogroups of public health concern (e.g. O157:H7, O26, O103) in this study indicated the need for mitigation strategies to ensure food safety by evaluating risk factors and management practices that contribute to the spread and prevalence of foodborne pathogens in a pre-harvest environment on DSSF.

A trait-based framework for predicting foodborne pathogen risk from wild birds

Recent foodborne illness outbreaks have heightened pressures on growers to deter wildlife from farms, jeopardizing conservation efforts. However, it remains unclear which species, particularly birds, pose the greatest risk to food safety. Using >11,000 pathogen tests and 1565 bird surveys covering 139 bird species from across the western United States, we examined the importance of 11 traits in mediating wild bird risk to food safety. We tested whether traits associated with pathogen exposure (e.g., habitat associations, movement, and foraging strategy) and pace-of-life (clutch size and generation length) mediated foodborne pathogen prevalence and proclivities to enter farm fields and defecate on crops. Campylobacter spp. were the most prevalent enteric pathogen (8.0%), while Salmonella and Shiga-toxin producing Escherichia coli (STEC) were rare (0.46% and 0.22% prevalence, respectively). We found that several traits related to pathogen exposure predicted pathogen prevalence. Specifically, Campylobacter and STEC-associated virulence genes were more often detected in species associated with cattle feedlots and bird feeders, respectively. Campylobacter was also more prevalent in species that consumed plants and had longer generation lengths. We found that species associated with feedlots were more likely to enter fields and defecate on crops. Our results indicated that canopy-foraging insectivores were less likely to deposit foodborne pathogens on crops, suggesting growers may be able to promote pest-eating birds and birds of conservation concern (e.g., via nest boxes) without necessarily compromising food safety. As such, promoting insectivorous birds may represent a win-win-win for bird conservation, crop production, and food safety. Collectively, our results suggest that separating crop production from livestock farming may be the best way to lower food safety risks from birds. More broadly, our trait-based framework suggests a path forward for co-managing wildlife conservation and food safety risks in farmlands by providing a strategy for holistically evaluating the food safety risks of wild animals, including under-studied species.

Salmonella enterica Serovar Diversity, Distribution, and Prevalence in Public Access Waters from a Central California Coastal Leafy Green Growing Region during 2011 - 2016

Prevalence and serovar diversity of Salmonella enterica was measured during a five-year survey of surface waters in a 500 mi^2 agricultural region of the Central California Coast. Rivers, streams, lakes, and ponds were sampled bimonthly resulting in 2,979 samples. Overall prevalence was 56.4% with higher levels detected in Spring than in Fall. Small, but significant, differences in prevalence were detected based on sample locations. Detection of Salmonella was correlated positively with both significant rain events and, in some environments, levels of generic Escherichia coli. Analysis of 1,936 isolates revealed significant serovar diversity, with 91 different serovars detected. The most common isolated serovars were S. enterica subsp. enterica serovars I 6,8:d:- (406 isolates, 21.0%, and potentially monophasic Salmonella Muenchen), Give (334 isolates, 17.3%), Muenchen (158 isolates, 8.2%), Typhimurium (227 isolates, 11.7%), Oranienburg (106 isolates, 5.5%), and Montevideo (78 isolates, 4%). Sixteen of the 24 most common serovars detected in the region are among the serovars reported to cause the most human salmonellosis in the United States. Some of the serovars were associated with location and seasonal bias. Analysis of XbaI Pulsed Field Gel Electrophoresis (PFGE) patterns of strains of serovars Typhimurium, Oranienburg, and Montevideo showed significant intra-serovar diversity. PFGE pulsotypes were identified in the region for multiple years of the survey, indicating persistence or regular re-introduction to the region. Importance Non-typhoidal Salmonella is the among the leading causes of bacterial foodborne illness and increasing numbers of outbreaks and recalls are due to contaminated produce. High prevalence and 91 different serovars were detected in this leafy green growing region. Seventeen serovars that cause most of the human salmonellosis in the United States were detected, with 16 of those serovars detected in multiple locations and multiple years of the 5-year survey. Understanding the widespread prevalence and diversity of Salmonella in the region will assist in promoting food safety practices and intervention methods for growers and regulators.

Two multistate outbreaks of a reoccurring Shiga toxin-producing Escherichia coli strain associated with romaine lettuce: USA, 2018-2019

Leafy green vegetables are a common source of Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) foodborne illness outbreaks. Ruminant animals, primarily cattle, are the major reservoir of STEC O157. Epidemiological, traceback and field investigations were conducted to identify potential outbreak sources. Product and environmental samples were tested for STEC. A reoccurring strain of STEC O157 caused two multistate outbreaks linked to romaine lettuce in 2018 and 2019, resulting in 234 illnesses in 33 states. Over 80% of patients interviewed consumed romaine lettuce before illness. The romaine lettuce was sourced from two California growing regions: Santa Maria and Salinas Valley in 2018 and Salinas Valley in 2019. The outbreak strain was isolated from environmental samples collected at sites >90 miles apart across growing regions, as well as from romaine-containing products in 2019. Although the definitive route of romaine contamination was undetermined, use of a contaminated agricultural water reservoir in 2018 and contamination from cattle grazing on adjacent land in 2019 were suspected as possible factors. Preventing lettuce contamination from growth to consumption is imperative to preventing illness. These outbreaks highlight the need to further understand mechanisms of romaine contamination, including the role of environmental or animal reservoirs for STEC O157.

Prevalence of multidrug resistance in Pseudomonas spp. isolated from wild bird feces in an urban aquatic environment

Antimicrobial resistance (AMR) has been detected in the microbiota of wildlife, yet little is known about the origin and impact within the ecosystem. Due to the shortage of nonepizootic surveillance, there is limited understanding of the natural prevalence and circulation of AMR bacteria in the wild animal population, including avian species. In this surveillance study, feces from wild birds in proximity to the River Cam, Cambridge, England, were collected and Pseudomonas spp. were isolated. Of the 115 samples collected, 24 (20.9%; 95% CI, 12.6%‒29.2%) harbored Pseudomonas spp. of which 18 (75%; 95% CI, 58%‒92%) had a multiple antibiotic resistance (MAR) index greater than 0.2. No Pseudomonas spp. isolate in this study was pansusceptible. Resistance was found among the 24 isolates against ciprofloxacin (87.5%; 95% CI, 74.3%‒100%) and cefepime (83.3%; 95% CI, 68.4%‒98.2%), both of which are extensively used to treat opportunistic Pseudomonas spp. infections. The prevalence of Pseudomonas spp. in the wild bird feces sampled during this study is greater than previous, similar studies. Additionally, their multidrug resistance profile provides insight into the potential risk for ecosystem contamination. It further highlights the importance of a One Health approach, including ongoing surveillance efforts that help to develop the understanding of how wildlife, including avifauna, may contribute and disperse AMR across the ecosystem.

Epidemiological investigations identified an outbreak of Shiga toxin-producing Escherichia coli serotype O26:H11 associated with pre-packed sandwiches

In October 2019, public health surveillance systems in Scotland identified an increase in the number of reported infections of Shiga toxin-producing Escherichia coli (STEC) O26:H11 involving bloody diarrhoea. Ultimately, across the United Kingdom (UK) 32 cases of STEC O26:H11 stx1a were identified, with the median age of 27 years and 64% were male; six cases were hospitalised. Among food exposures there was an association with consuming pre-packed sandwiches purchased at outlets belonging to a national food chain franchise (food outlet A) [odds ratio (OR) = 183.89, P < 0.001]. The common ingredient identified as a component of the majority of the sandwiches sold at food outlet A was a mixed salad of Apollo and Iceberg lettuce and spinach leaves. Microbiological testing of food and environmental samples were negative for STEC O26:H11, although STEC O36:H19 was isolated from a mixed salad sample taken from premises owned by food outlet A. Contamination of fresh produce is often due to a transient event and detection of the aetiological agent in food that has a short-shelf life is challenging. Robust, statistically significant epidemiological analysis should be sufficient evidence to direct timely and targeted on-farm investigations. A shift in focus from testing the microbiological quality of the produce to investigating the processes and practices through the supply chain and sampling the farm environment is recommended.

Prevalence and Epidemiology of Non-O157 Escherichia coli Serogroups O26, O103, O111, and O145 and Shiga Toxin Gene Carriage in Scottish Cattle, 2014-2015

Cattle are reservoirs for Shiga toxin Escherichia coli (STEC), bacteria shed in animal feces. Humans are infected through consumption of contaminated food or water and by direct contact, causing serious disease and kidney failure in the most vulnerable.

Cattle are a reservoir for Shiga toxin-producing Escherichia coli (STEC), zoonotic pathogens that cause serious clinical disease. Scotland has a higher incidence of STEC infection in the human population than the European average. The aim of this study was to investigate the prevalence and epidemiology of non-O157 serogroups O26, O103, O111, and O145 and Shiga toxin gene carriage in Scottish cattle. Fecal samples (n = 2783) were collected from 110 herds in 2014 and 2015 and screened by real-time PCR. Herd-level prevalence (95% confidence interval [CI]) for O103, O26, and O145 was estimated as 0.71 (0.62, 0.79), 0.43 (0.34, 0.52), and 0.23 (0.16, 0.32), respectively. Only two herds were positive for O111. Shiga toxin prevalence was high in both herds and pats, particularly for stx₂ (herd level: 0.99; 95% CI: 0.94, 1.0). O26 bacterial strains were isolated from 36 herds on culture. Fifteen herds yielded O26 stx-positive isolates that additionally harbored the intimin gene; six of these herds shed highly pathogenic stx₂-positive strains. Multiple serogroups were detected in herds and pats, with only 25 herds negative for all serogroups. Despite overlap in detection, regional and seasonal effects were observed. Higher herd prevalence for O26, O103, and stx₁ occurred in the South West, and this region was significant for stx₂ at the pat level (P = 0.015). Significant seasonal variation was observed for O145 prevalence, with the highest prevalence in autumn (P = 0.032). Negative herds were associated with Central Scotland and winter. Herds positive for all serogroups were associated with autumn and larger herd size and were not housed at sampling.

IMPORTANCE Cattle are reservoirs for Shiga toxin-producing Escherichia coli (STEC), bacteria shed in animal feces. Humans are infected through consumption of contaminated food or water and by direct contact, resulting in serious disease and kidney failure in the most vulnerable. The contribution of non-O157 serogroups to STEC illness was underestimated for many years due to the lack of specific tests. Recently, non-O157 human cases have increased, with O26 STEC of particular note. It is therefore vital to investigate the level and composition of non-O157 in the cattle reservoir and to compare them historically and by the clinical situation. In this study, we found cattle prevalence high for toxin, as well as for O103 and O26 serogroups. Pathogenic O26 STEC were isolated from 14% of study herds, with toxin subtypes similar to those seen in Scottish clinical cases. This study highlights the current risk to public health from non-O157 STEC in Scottish cattle.

Epidemiological investigation of recurrent outbreaks of haemolytic uraemic syndrome caused by Shiga toxin-producing Escherichia coli serotype O55:H7 in England, 2014-2018

Recurrent outbreaks of haemolytic uraemic syndrome (HUS) caused by Shiga toxin-producing Escherichia coli (STEC) serotype O55:H7 occurred in England between 2014 and 2018. We reviewed the epidemiological evidence to identify potential source(s) and transmission routes of the pathogen, and to assess the on-going risk to public health. Over the 5-year period, there were 43 confirmed and three probable cases of STEC O55:H7. The median age of cases was 4 years old (range 6 months to 69 years old) and over half of all cases were female (28/46, 61%). There were 36/46 (78.3%) symptomatic cases, and over half of all cases developed HUS (25/46, 54%), including two fatal cases. No common food or environmental exposures were identified, although the majority of cases lived in rural or semi-rural environments and reported contact with both wild and domestic animals. This investigation informed policy on the clinical and public health management of HUS caused by STEC other than serotype O157:H7 (non-O157 STEC) in England, including comprehensive testing of all household contacts and household pets and more widespread use of polymerase chain reaction assays for the rapid diagnosis of STEC-HUS.

The under-investigated wild side of Escherichia coli: genetic diversity, pathogenicity and antimicrobial resistance in wild animals

A striking paucity of information exists on Escherichia coli in wild animals despite evidence that they harbour pathogenic and antimicrobial-resistant E. coli in their gut microbiomes and may even serve as melting pots for novel genetic combinations potentially harmful to human health. Wild animals have been implicated as the source of pathogenic E. coli outbreaks in agricultural production, but a lack of knowledge surrounding the genetics of E. coli in wild animals complicates source tracking and thus contamination curtailment efforts. As human populations continue to expand and invade wild areas, the potential for harmful microorganisms to transfer between humans and wildlife increases. Here, we conducted a literature review of the small body of work on E. coli in wild animals. We highlight the geographic and host taxonomic coverage to date, and in each, identify significant gaps. We summarize the current understanding of E. coli in wild animals, including its genetic diversity, host and geographic distribution, and transmission pathways within and between wild animal and human populations. The knowledge gaps we identify call for greater research efforts to understand the existence of E. coli in wild animals, especially in light of the potentially strong implications for global public health.

Assessing the Food Safety Risk Posed by Birds Entering Leafy Greens Fields in the US Southwest

In the US Southwest, it is common to observe birds in leafy green fields, though the risk they contribute to foodborne outbreaks remains unclear. In this study, we investigated and recorded the relationship between birds near leafy green fields and the risk for contaminated irrigation water or leafy green plants. We monitored the presence of birds for over two years and performed cloacal swab analysis for non-pathogenic Escherichia coli, E. coli O157:H7 and Salmonellaenterica, while also monitoring the incidence of other microbial indicators. We also assessed the risks from bird feces by performing observations in a commercial field reported with Salmonella positive samples and by analyzing the survival of foodborne pathogens in bird feces. Our results showed that most of the birds near the crop fields were resident small birds. We did not observe a correlation between the number of birds in sites and the incidence of indicator bacteria (e.g., coliforms, E. coli) in irrigation canal water, with the exception of one out of four sites where water flow was low or stagnant. Using walk-in-traps, 305 birds were captured and placed in short-term captivity to determine the presence of various bacteria. None of the birds tested positive for E. coli O157:H7 or Salmonella. However, nearly 40% of the birds captured were confirmed positive for non-pathogenic E. coli. We found no correlation between age (young, adult, unknown), gender (male, female, unknown) and the incidence of E. coli positive birds, but we observed significantly higher probability of incidence during October-December. The role of relative humidity and temperature on bacterial survival appeared to play a key role in the survival of Salmonella on the leaves of spinach plants in a commercial field. This was also confirmed in laboratory conditions where Salmonella inoculated in bird feces and exposed to 15 °C and 80% RH(Relative humidity) survived beyond 133 days, while at 26 °C and 40% RH, the organism was undetectable after 63 days. Our results suggest that local birds associated with leafy green fields likely pose a minimal impact of risk for food contamination, but also points out the need for increased analysis specifically for E. coli O157:H7. Furthermore, our study suggests the need for expanding research that addresses risks associated with large migratory birds, especially in areas where stagnated water sources would be used for overhead sprinkle irrigation.

Shifts in species interactions and farming contexts mediate net effects of birds in agroecosystems

Some birds are viewed as pests and vectors of foodborne pathogens in farmlands, yet birds also benefit growers by consuming pests. While many growers seek to prevent birds from accessing their farms, few studies have attempted to quantify the net effects of bird services and disservices, let alone how net effects shift across farm management strategies. We quantified the net effect of birds on crop production across 20 California strawberry (Fragaria × ananassa) farms that varied in local management practices and landscape context. We surveyed farms for berry damage and bird droppings (as potential sources of pathogens) and implemented a large-scale exclusion experiment to quantify the impact of birds on production. We found that birds had only a slightly negative overall impact on strawberry production, reducing economic value by 3.6%. Direct bird damage and intraguild predation contributed equally to this net effect, underscoring the importance of indirect trophic interactions that may be less apparent to growers. In simple landscapes (e.g., low proportions of surrounding seminatural habitat), birds provided pest control in the interiors of farm fields, and costs from bird damage to crops peaked at field edges. In complex landscapes (e.g., high proportions of seminatural habitat), birds were more likely to disrupt pest control by feeding as intraguild predators. Nonetheless, seminatural habitat dampened bird services and disservices, and our models predicted that removing habitat around farm fields would increase costs from bird damage to crops by up to 76%. Fecal contamination of crops was extremely rare (0.01%). However, both fecal contamination and bird damage did increase on farms with higher densities of fencing and wires, where birds often perch. Our results demonstrate that maintaining seminatural habitat around farms may enhance bird diversity and mitigate bird damage without increasing food safety risks. We also show that the net effects of birds depend on farming context and vary in complex ways in relation to locations within a farm, local farm attributes, and the surrounding landscape. This context-specific variation must be considered in order to optimize the management of wild birds in agroecosystems.