The rabbit as a new reservoir host of enterohemorrhagic Escherichia coli

A One Health Perspective for Defining and Deciphering Escherichia coli Pathogenic Potential in Multiple Hosts

E. coli is one of the most common species of bacteria colonizing humans and animals. The singularity of E. coli 's genus and species underestimates its multifaceted nature, which is represented by different strains, each with different combinations of distinct virulence factors. In fact, several E. coli pathotypes, or hybrid strains, may be associated with both subclinical infection and a range of clinical conditions, including enteric, urinary, and systemic infections. E. coli may also express DNA-damaging toxins that could impact cancer development. This review summarizes the different E. coli pathotypes in the context of their history, hosts, clinical signs, epidemiology, and control. The pathotypic characterization of E. coli in the context of disease in different animals, including humans, provides comparative and One Health perspectives that will guide future clinical and research investigations of E. coli infections.

Cytotoxic Escherichia coli strains encoding colibactin, cytotoxic necrotizing factor, and cytolethal distending toxin colonize laboratory common marmosets (Callithrix jacchus)

Cyclomodulins are virulence factors that modulate cellular differentiation, apoptosis, and proliferation. These include colibactin (pks), cytotoxic necrotizing factor (cnf), and cytolethal distending toxin (cdt). Pathogenic pks+, cnf+, and cdt+ E. coli strains are associated with inflammatory bowel disease (IBD) and colorectal cancer in humans and animals. Captive marmosets are frequently afflicted with IBD-like disease, and its association with cyclomodulins is unknown. Cyclomodulin-encoding E. coli rectal isolates were characterized using PCR-based assays in healthy and clinically affected marmosets originating from three different captive sources. 139 E. coli isolates were cultured from 122 of 143 marmosets. The pks gene was detected in 56 isolates (40%), cnf in 47 isolates (34%), and cdt in 1 isolate (0.7%). The prevalences of pks+ and cnf+ E. coli isolates were significantly different between the three marmoset colonies. 98% of cyclomodulin-positive E. coli belonged to phylogenetic group B2. Representative isolates demonstrated cyclomodulin cytotoxicity, and serotyping and whole genome sequencing were consistent with pathogenic E. coli strains. However, the presence of pks+, cnf+, or cdt+ E. coli did not correlate with clinical gastrointestinal disease in marmosets. Cyclomodulin-encoding E. coli colonize laboratory common marmosets in a manner dependent on the source, potentially impacting reproducibility in marmoset models.

Intestinal colonization of genotoxic Escherichia coli strains encoding colibactin and cytotoxic necrotizing factor in small mammal pets

Escherichia coli encoding colibactin (clb), cytolethal distending toxin (cdt), and hemolysin-associated cytotoxic necrotizing factor (cnf) are associated with various intestinal and extra-intestinal diseases in humans and animals. Small mammal pets are not evaluated for genotoxin-encoding E. coli. Thus, the prevalence of such strains is unknown. The objective of this study was to isolate and characterize genotoxin-encoding E. coli from healthy and ill small mammal pets examined at a veterinary clinic and at two animal adoption centers. E. coli isolates were cultured from fecal samples and biochemically characterized. A total of 65 animals, including mice, rats, rabbits, guinea pigs, and hedgehogs, were screened. Twenty-six E. coli isolates were obtained from 24 animals. Twelve of the 26 isolates (46.2 %) were PCR-positive for the pks genes clbA and clbQ. Two isolates (7.7 %) were PCR-positive for cnf. All isolates were PCR-negative for cdt. All genotoxin-encoding isolates belonged to the pathogen-associated phylogenetic group B2. Representative genotoxin-encoding isolates had serotypes previously associated with clinical disease in humans and animals. Isolates encoding pks or cnf induced megalocytosis and cytotoxicity to HeLa cells in vitro. Although most isolates were obtained from healthy pets, two guinea pigs with diarrhea had pks-positive isolates cultured from their feces. Whole genome sequencing on four representative isolates confirmed the presence of pks and cnf genes and identified other virulence factors associated with pathogenicity in animals and humans. Our results suggest that small mammalian pets may serve as a reservoir for potentially pathogenic E. coli and implicate a zoonotic risk.

Colonization, mortality, and host cytokines response to enterohemorrhagic Escherichia coli in rabbits

The major virulence factor of enterohemorrhagic Escherichia coli in infections is its ability to cause attaching and effacing lesions in enterocytes, as well as to produce Shiga toxins. To clarify the pathogenic mechanism and host innate immune responses of enterohemorrhagic Escherichia coli in rabbits, experimental infections with TS and MY strains were conducted. Among the results, although the MY strain's pathogenicity was stronger than the TS, typical symptoms were observed in both groups of bacterial-infected rabbits. Pathological changes in the heart, liver, and spleen of rabbits infected with the MY strain were more severe than those infected with the TS strain, pro-inflammatory cytokines IL-1β, IL-6, IL-8, IFN-γ, and TNF-α were induced by both strains, and α- and β-defensin were significantly upregulated at 3 d postinfection. Moreover, in the spleen, the MY strain induced greater expressions of α- and β-defensins than did the TS strain. However, in the liver, the TS strain induced greater expressions of α- and β-defensins than did the MY strain. Most likely, different replications of the MY and TS strains in the liver and spleen induced different host immune responses. Altogether, the findings provide new insights into the occurrence and development of enterohemorrhagic Escherichia coli-mediated diseases in rabbits.

Survival of Escherichia coli on Lettuce under Field Conditions Encountered in the Northeastern United States

Although wildlife intrusion and untreated manure have been associated with microbial contamination of produce, relatively few studies have examined the survival of Escherichia coli on produce under field conditions following contamination (e.g., via splash from wildlife feces). This experimental study was performed to estimate the die-off rate of E. coli on preharvest lettuce following contamination with a fecal slurry. During August 2015, field-grown lettuce was inoculated via pipette with a fecal slurry that was spiked with a three-strain cocktail of rifampin-resistant nonpathogenic E. coli. Ten lettuce heads were harvested at each of 13 time points following inoculation (0, 2.5, 5, and 24 h after inoculation and every 24 h thereafter until day 10). The most probable number (MPN) of E. coli on each lettuce head was determined, and die-off rates were estimated. The relationship between sample time and the log MPN of E. coli per head was modeled using a segmented linear model. This model had a breakpoint at 106 h (95% confidence interval = 69, 142 h) after inoculation, with a daily decrease of 0.70 and 0.19 log MPN for 0 to 106 h and 106 to 240 h following inoculation, respectively. These findings are consistent with die-off rates obtained in similar studies that assessed E. coli survival on produce following irrigation. Overall, these findings provide die-off rates for E. coli on lettuce that can be used in future quantitative risk assessments.

Biosecurity practices and causes of enteritis on Ontario meat rabbit farms

Infectious enterocolitis is a significant cause of mortality in meat rabbits. Disease risk is enhanced by intensive rearing practices and poor on-farm biosecurity. This investigation was undertaken in farmed meat rabbits during an Ontario-wide outbreak of enteritis with high mortality to determine the prevalence of causative agents. A survey evaluating on-farm biosecurity practices was also conducted to identify potential means of pathogen contamination and zoonotic risks. Gross and microscopic pathology evaluations combined with microbiologic testing were conducted on 95 rabbits over spring and winter months. Escherichia coli and Clostridium spiroforme were most commonly associated with enteritis in rabbits regardless of age or season and lesions were significantly more severe in mature does (P < 0.0001). The survey results demonstrated a lack of consistent on-farm biosecurity practices. The infectious nature of enteric disease of rabbits combined with poor biosecurity practices may contribute to disease transmission within and between farms.

Biology and Diseases of Rabbits

Beginning in 1931, an inbred rabbit colony was developed at the Phipps Institute for the Study, Treatment and Prevention of Tuberculosis at the University of Pennsylvania. This colony was used to study natural resistance to infection with tuberculosis (Robertson et al., 1966). Other inbred colonies or well-defined breeding colonies were also developed at the University of Illinois College of Medicine Center for Genetics, the Laboratories of the International Health Division of The Rockefeller Foundation, the University of Utrecht in the Netherlands, and Jackson Laboratories. These colonies were moved or closed in the years to follow. Since 1973, the U.S. Department of Agriculture has reported the total number of certain species of animals used by registered research facilities (1997). In 1973, 447,570 rabbits were used in research. There has been an overall decrease in numbers of rabbits used. This decreasing trend started in the mid-1990s. In 2010, 210,172 rabbits were used in research. Despite the overall drop in the number used in research, the rabbit is still a valuable model and tool for many disciplines.

Animal Reservoirs of Shiga Toxin-Producing Escherichia coli

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

Helicobacter canis colonization in sheep: a Zoonotic link

BACKGROUND

Helicobacter canis has been associated with hepatobiliary and gastrointestinal disease in dogs, cats, and humans. Infection has not been documented in other species.

MATERIALS AND METHODS

Sheep feces subjected to microaerobic culture. Isolates were characterized by genus-specific PCR, restriction fragment length polymorphism, biochemical profiling, and 16S rRNA sequence analysis.

RESULTS

Helicobacter canis was isolated from sheep feces and confirmed by the above methods. These isolates are distinct from other sheep-origin enterohepatic Helicobacter species previously isolated.

CONCLUSIONS

This study identifies sheep as H. canis reservoirs potentially important in zoonotic or foodborne transmission.

Prevalence of diarrhea-associated virulence genes and genetic diversity in Escherichia coli isolates from fecal material of various animal hosts

In order to assess the health risk associated with a given source of fecal contamination using bacterial source tracking (BST), it is important to know the occurrence of potential pathogens as a function of host. Escherichia coli isolates (n=593) from the feces of diverse animals were screened for various virulence genes: stx1 and stx2 (Shiga toxin-producing E. coli [STEC]), eae and EAF (enteropathogenic E. coli [EPEC]), STh, STp, and LT (enterotoxigenic E. coli [ETEC]), and ipaH (enteroinvasive E. coli [EIEC]). Eleven hosts were positive for only the eae (10.11%) gene, representing atypical EPEC, while two hosts were positive for both eae and EAF (1.3%), representing typical EPEC. stx1, stx2, or both stx1 and stx2 were present in 1 (0.1%,) 10 (5.56%), and 2 (1.51%) hosts, respectively, and confirmed as non-O157 by using a E. coli O157 rfb (rfbO157) TaqMan assay. STh and STp were carried by 2 hosts (2.33%) and 1 host (0.33%), respectively, while none of the hosts were positive for LT and ipaH. The repetitive element palindromic PCR (rep-PCR) fingerprint analysis identified 221 unique fingerprints with a Shannon diversity index of 2.67. Multivariate analysis of variance revealed that majority of the isolates clustered according to the year of sampling. The higher prevalence of atypical EPEC and non-O157 STEC observed in different animal hosts indicates that they can be a reservoir of these pathogens with the potential to contaminate surface water and impact human health. Therefore, we suggest that E. coli from these sources must be included while constructing known source fingerprint libraries for tracking purposes. However, the observed genetic diversity and temporal variation need to be considered since these factors can influence the accuracy of BST results.

Virulence of the Shiga toxin type 2-expressing Escherichia coli O104:H4 German outbreak isolate in two animal models

In May 2011, a large food-borne outbreak was traced to an unusual O104:H4 enteroaggregative Escherichia coli (EAEC) strain that produced Shiga toxin (Stx) type 2 (Stx2). We developed a mouse model to study the pathogenesis and treatment for this strain and examined the virulence of the isolate for Dutch belted rabbits. O104:H4 strain C227-11 was gavaged into C57BL/6 mice at 10(9) to 10(11) CFU/animal. The infected animals were then given water with ampicillin (Amp; 5 g/liter) ad libitum. The C227-11-infected, Amp-treated C57BL/6 mice exhibited both morbidity and mortality. Kidneys from mice infected with C227-11 showed acute tubular necrosis, a finding seen in mice infected with typical Stx-producing E. coli. We provided anti-Stx2 antibody after infection and found that all of the antibody-treated mice gained more weight than untreated mice and, in another study, that all of the antibody-treated animals lived, whereas 3/8 phosphate-buffered saline-treated mice died. We further compared the pathogenesis of C227-11 with that of an Stx-negative (Stx(-)) O104:H4 isolate, C734-09, and an Stx2(-) phage-cured derivative of C227-11. Whereas C227-11-infected animals lost weight or gained less weight over the course of infection and died, mice infected with either of the Stx(-) isolates did not lose weight and only one mouse died. When the Stx-positive (Stx(+)) and Stx2(-) O104:H4 strains were compared in rabbits, greater morbidity and mortality were observed in rabbits infected with the Stx2(+) isolates than the Stx2(-) isolates. In conclusion, we describe two animal models for EAEC pathogenesis, and these studies show that Stx2 is responsible for most of the virulence observed in C227-11-infected mice and rabbits.

Enteropathogenic Escherichia coli prevalence in laboratory rabbits

Rabbit-origin enteropathogenic Escherichia coli (EPEC) causes substantial diarrhea-associated morbidity and has zoonotic potential. A culture-based survey was undertaken to ascertain its prevalence. EPEC was isolated from 6/141 (4.3%) commercially-acquired laboratory rabbits. Three of these did not have diarrhea or EPEC-typical intestinal lesions; they instead had background plasmacytic intestinal inflammation. Asymptomatically infected rabbits may function as EPEC reservoirs.

Enzootic enteropathogenic Escherichia coli infection in laboratory rabbits

Enteropathogenic Escherichia coli (EPEC) is the most important cause of persistent diarrhea in children, particularly in developing countries. Animals serve as pathogenic E. coli reservoirs, and compelling evidence for cross-species EPEC transmission exists. In this report, enzootic EPEC infection associated with up to 10.5% diarrhea-associated morbidity in a large laboratory Dutch Belted rabbit colony was investigated. These rabbits were obtained from a commercial vendor and had acute diarrhea following shipment. Fecal culture of 20 rabbits yielded 48 E. coli isolates, 83% of which were eae positive. Repetitive sequence-based PCR (REP-PCR) and serologic analysis identified a single disease-associated EPEC O145:H2 strain. In sampled rabbits, EPEC-positive culture and the presence of diarrhea were significantly associated. This strain displayed a localized adherence-like HEp-2 cell adherence pattern, as seen in diarrheic human infant EPEC isolates. Treatment was instituted with the fluoroquinolone antibiotic enrofloxacin, to which all isolates were susceptible. Preshipment parenteral enrofloxacin administration reduced diarrhea-associated morbidity 22-fold and mortality 12-fold in subsequent deliveries. This report emphasizes the zoonotic potential of animal EPEC strains and the need for virulence determinant-based screening of E. coli isolates from diarrheic animals.

Zoonoses of rabbits and rodents

Millions of households in the US own rabbits or rodents, including hamsters, guinea pigs, and gerbils. Activities such as hunting and camping also involve human interactions with wild rabbits and rodents. In many environments, feral rabbits and rodents live in close proximity to humans, domesticated animals, and other wildlife. Education of rodent and rabbit owners and individuals with occupational or recreational exposures to these species is paramount to reduce the prevalence of zoonoses associated with rabbit and rodent exposure.

Shiga toxin: expression, distribution, and its role in the environment

In this review, we highlight recent work that has increased our understanding of the production and distribution of Shiga toxin in the environment. Specifically, we review studies that offer an expanded view of environmental reservoirs for Shiga toxin producing microbes in terrestrial and aquatic ecosystems. We then relate the abundance of Shiga toxin in the environment to work that demonstrates that the genetic mechanisms underlying the production of Shiga toxin genes are modified and embellished beyond the classical microbial gene regulatory paradigms in a manner that apparently "fine tunes" the trigger to modulate the amount of toxin produced. Last, we highlight several recent studies examining microbe/protist interactions that postulate an answer to the outstanding question of why microbes might harbor and express Shiga toxin genes in the environment.

Novel calicivirus identified in rabbits, Michigan, USA

This virus is distinct from rabbit hemorrhagic disease virus.

We report a disease outbreak in a Michigan rabbitry of a rabbit calicivirus distinct from the foreign animal disease agent, rabbit hemorrhagic disease virus (RHDV). The novel virus has been designated Michigan rabbit calicivirus (MRCV). Caliciviruses of the Lagovirus genus other than RHDV have not been described in US rabbit populations. The case-fatality rate was 32.5% (65/200). Clinical signs included hemorrhage and sudden death, with hepatic necrosis. Analysis of viral RNA sequence from >95% of the viral genome showed an average similarity of 79% with RHDV. Similarity of the predicted MRCV capsid amino acid sequence ranged from 89.8% to 91.3%, much lower than the 98% amino acid similarity between RHDV strains. Experimentally infected rabbits lacked clinical disease, but MRCV was detected in tissues by PCR. We propose that MRCV primarily causes subclinical infection but may induce overt RHD-like disease under certain field conditions.

Shedding of food-borne pathogens and microbiological carcass contamination in rabbits at slaughter

To obtain microbiological data from rabbits at slaughter, 500 fecal samples and 500 carcasses samples were examined. All samples tested negative for Listeria and Salmonella. Campylobacter were detected in two fecal samples. Of the 500 fecal samples, 45.8% tested positive for eae (intimin), 1.2% for stx (Shiga toxin), and 1.8% for both eae and stx. By colony hybridization, 56 eae positive Escherichia coli strains were isolated. Among them, 27 strains (48.2%) were of the serotypes O178:H7 and O153:H7, whereas 15 strains (26.8%) belonged to a serogroup that has not yet been described (O(CB10681):H7). All strains possessed intimin beta1 and the translocated intimin receptor (tir) capable of being tyrosine phosphorylated. None of the strains harbored the genes for Shiga toxins, EAST1 (astA), bundlin (bfpA), or the EAF plasmid. Slaughter rabbits therefore constitute a reservoir for certain atypical enteropathogenic Escherichia coli. On rabbit carcasses, average total bacterial counts accounted for 3.3 log CFU cm(-2). Enterobacteriaceae and coagulase positive staphylococci (CPS) were detected on 118 (23.6%) and 153 (30.6%) carcasses, respectively. Enterobacteriaceae and CPS counts of positive samples were mainly <1.5 log CFU cm(-2). Among 153 selected CPS isolates, 98.7% were identified as Staphylococcus aureus. None of the 151 isolated strains harbored the gene for methicillin resistance (mecA). Genes for staphylococcal enterotoxins (SE) were detected in 102 strains. The combinations of seg and sei (53 strains) and sed, seg, sei, and sej (27 strains) dominated.

Protection against Shiga toxin-producing Escherichia coli infection by transcutaneous immunization with Shiga toxin subunit B

Enterohemorrhagic Escherichia coli (EHEC) strains are important human food-borne pathogens. EHEC strains elaborate potent Shiga toxins (Stx1, and/or Stx2) implicated in the development of hemorrhagic colitis (HC) or hemolytic-uremic syndrome (HUS). In this report, we evaluated the immunogenicity and protective efficacy of Stx1 subunit B (StxB1) administered by transcutaneous immunization (TCI). Three groups of Dutch Belted rabbits received patches containing StxB1, StxB1 in combination with Escherichia coli heat-labile enterotoxin (LT), or LT alone. An additional group of naïve rabbits served as controls. The protective efficacy following TCI with StxB1 was assessed by challenging rabbits with a virulent Stx1-producing strain, RDEC-H19A, capable of inducing HC and HUS in rabbits. Antibodies specific to StxB1 from serum and bile samples were determined by enzyme-linked immunosorbent assay and toxin neutralization test. Rabbits immunized with StxB1 demonstrated improved weight gain and reduced Stx-induced histopathology. Rabbits receiving StxB or StxB1/LT showed a significant increase in serum immunoglobulin G titers specific to StxB1 as well as toxin neutralization titers. These data demonstrated that the StxB delivered by TCI could induce significant systemic immune responses. Thus, Stx subunit B vaccine delivered by a patch for a high-risk population may be a practical approach to prevent (and/or reduce) Stx-induced pathology.

Rabbit meat as a source of bacterial foodborne pathogens

Even though worldwide production of rabbit meat is >1,000,000 tons, little information is available for rabbit meat microbiology. This study provides data on the prevalence of Salmonella, Escherichia coli O157:H7, Yersinia enterocolitica, Listeria spp., motile Aeromonas spp., and Staphylococcus aureus on rabbit meat. A total of 24 rabbit carcasses from two abattoirs and 27 rabbit meat packages from supermarket displays were examined. In addition to culturing methods, associated virulence genes were investigated by PCR in suspect isolates and samples. Neither Salmonella nor E. coli O157:H7 was detected. All samples were negative for virulence-associated invA, stx1, and stx2 genes. At one abattoir, two carcasses (3.9%) carried Y. enterocolitica yst-, and two were positive for the yst gene, although viable Y. enterocolitica cells were not recovered from these samples. Seven samples (13.7%) were contaminated with Listeria. Of them, three were positive for hly and iap genes (Listeria monocytogenes hly+ / iap+), two carried Listeria seeligeri, one carried Listeria ivanovii, and one carried Listeria innocua. For detectable motile Aeromonas spp. (average count, 1.77 +/- 0.62 log CFU/g), the contamination rate was 35.3%, although ca. 90% of the samples were positive for the aerA and/or hlyA genes. The majority of aeromonad isolates were Aeromonas hydrophila aerA+ / hlyA+. Aeromonas caviae, Aeromonas popoffii, Aeromonas schubertii, and the two biovars of Aeromonas veronii were also isolated. The prevalence of S. aureus contamination (average count, 1.37 +/- 0.79 log CFU/g) was 52.9%. Among 27 S. aureus isolates, two harbored genes for staphylococcal enterotoxin B (seb), and two harbored genes for staphylococcal enterotoxin C (sec). The remaining isolates were negative for sea, seb, sec, sed, and see.

Occurrence of Escherichia coli in Wildlife from Different Habitats of Sarawak, Malaysia

This study was carried out to assess the occurrence of Escherichia coli (E. coli) in the bats, birds and rodents asrepresentative of wildlife from different habitats in Sibu and Kapit, Sarawak, Malaysia. A total of 682 swabsamples were collected from wildlife hosts and screened for the bacteria E. coli and E. coli O157:H7 usingstandard microbiological methods and molecular techniques. The overall occurrence rates of E. coli among thesehosts were 14%, 17% and 54% for bats, birds and rodents, respectively. The occurrence of E. coli was thehighest in rodents regardless of the habitats. Isolated E. coli were then screened for E. coli O157:H7 by using amultiplex PCR with four primer pairs targeting for Shiga toxin producing genes (slt-I and slt-II), and the genesinvolved in biosynthesis of O157 antigen (rfbE) and H7 antigen (fliCH7 ). slt-I, slt-II and rfbE genes were notdetected in any of the E. coli isolates. However, the gene encoding for H7 antigen was detected in 23 E. coliisolates. This indicated that E. coli O157:H7 strain was not detected in the wildlife studied. Absence of E. coliO157:H7 in the wildlife studied indicated these wild animals do not serve as an important reservoir of E. coliO157:H7. However, precautions have to be taken as other group of pathogenic E. coli may pose a zoonotic riskfor humans and other animals.