Characterisation of typical enteropathogenic Escherichia coli (tEPEC) lineages and novel bfpA variants detected in Australian fruit bats (Pteropus poliocephalus)

Enteropathogenic Escherichia coli (EPEC) is an important cause of diarrhoeal disease in human infants. EPEC strains are defined by the presence of specific virulence factors including intimin (encoded by the eae gene) and bundle forming pili (Bfp). Bfp is encoded by the bfp operon and includes the bfpA gene for the major pilus subunit. By definition, Bfp are only present in typical EPEC (tEPEC), for which, humans are considered to be the only known natural host. This study detected tEPEC in faecal samples from a wild Australian fruit bat species, the grey-headed flying-fox (Pteropus poliocephalus). Whole genome sequencing of 61 E. coli isolates from flying-foxes revealed that 21.3 % (95%CI: 13 %-33 %) were tEPEC. Phylogenetic analyses showed flying-fox tEPEC shared evolutionary lineages with human EPEC, but were predominantly novel sequence types (9 of 13) and typically harboured novel bfpA variants (11 of 13). HEp-2 cell adhesion assays showed adherence to human-derived epithelial cells by all 13 flying-fox tEPEC, indicating that they all carried functional Bfp. Using an EPEC-specific duplex PCR, it was determined that tEPEC comprised 17.4 % (95%CI: 13 %-22 %) of 270 flying-fox E. coli isolates. Furthermore, a tEPEC-specific multiplex PCR detected the eae and bfpA virulence genes in 18.0 % (95%CI: 8.0 %-33.7 %) of 506 flying-fox faecal DNA samples, with occurrences ranging from 1.3 % to 87.0 % across five geographic areas sampled over a four-year period. The identification of six novel tEPEC sequence types and five novel bfpA variants suggests flying-foxes carry bat-specific tEPEC lineages. However, their close relationship with human EPEC and functional Bfp, indicates that flying-fox tEPEC have zoonotic potential and that dissemination of flying-fox tEPEC into urban environments may pose a public health risk. The consistent detection of tEPEC in flying-foxes over extensive geographical and temporal scales indicates that both wild grey-headed flying-foxes and humans should be regarded as natural tEPEC hosts.

The Population Genomics of Increased Virulence and Antibiotic Resistance in Human Commensal Escherichia coli over 30 Years in France

Escherichia coli is a commensal species of the lower intestine but is also a major pathogen causing intestinal and extraintestinal infections that is increasingly prevalent and resistant to antibiotics. Most studies on genomic evolution of E. coli used isolates from infections. Here, instead, we whole-genome sequenced a collection of 403 commensal E. coli isolates from fecal samples of healthy adult volunteers in France (1980 to 2010). These isolates were distributed mainly in phylogroups A and B2 (30% each) and belonged to 152 sequence types (STs), the five most frequent being ST10 (phylogroup A; 16.3%), ST73 and ST95 (phylogroup B2; 6.3 and 5.0%, respectively), ST69 (phylogroup D; 4.2%), and ST59 (phylogroup F; 3.9%), and 224 O:H serotypes. ST and serotype diversity increased over time. The O1, O2, O6, and O25 groups used in bioconjugate O-antigen vaccine against extraintestinal infections were found in 23% of the strains of our collection. The increase in frequency of virulence-associated genes and antibiotic resistance was driven by two evolutionary mechanisms. Evolution of virulence gene frequency was driven by both clonal expansion of STs with more virulence genes ("ST-driven") and increases in gene frequency within STs independent of changes in ST frequencies ("gene-driven"). In contrast, the evolution of resistance was dominated by increases in frequency within STs ("gene-driven"). This study provides a unique picture of the phylogenomic evolution of E. coli in its human commensal habitat over 30 years and will have implications for the development of preventive strategies. IMPORTANCE Escherichia coli is an opportunistic pathogen with the greatest burden of antibiotic resistance, one of the main causes of bacterial infections and an increasing concern in an aging population. Deciphering the evolutionary dynamics of virulence and antibiotic resistance in commensal E. coli is important to understand adaptation and anticipate future changes. The gut of vertebrates is the primary habitat of E. coli and probably where selection for virulence and resistance takes place. Unfortunately, most whole-genome-sequenced strains are isolated from pathogenic conditions. Here, we whole-genome sequenced 403 E. coli commensals isolated from healthy French subjects over a 30-year period. Virulence genes increased in frequency by both clonal expansion of clones carrying them and increases in frequency within clones, whereas resistance genes increased by within-clone increased frequency. Prospective studies of E. coli commensals should be performed worldwide to have a broader picture of evolution and adaptation of this species.

Fecal Shedding of Multidrug Resistant Escherichia coli Isolates in Dogs Fed with Raw Meat-Based Diets in Brazil

The practice of feeding dogs raw meat-based diets (RMBDs) is growing in several countries, and the risks associated with the ingestion of pathogenic and antimicrobial-resistant Escherichia coli in dogs fed these diets are largely unknown. We characterized E. coli strains isolated from dogs fed either an RMBD or a conventional dry feed, according to the phylogroup, virulence genes, and antimicrobial susceptibility profiles of the bacteria. Two hundred and sixteen E. coli strains were isolated. Dogs fed RMBDs shed E. coli strains from the phylogroup E more frequently and were positive for the E. coli heat-stable enterotoxin 1-encoding gene. Isolates from RMBD-fed dogs were also frequently positive for multidrug-resistant E. coli isolates including extended-spectrum beta-lactamase (ESBL) producers. Whole-genome sequencing of seven ESBL-producing E. coli strains revealed that they predominantly harbored blaCTX-M-55, and two strains were also positive for the colistin-resistant gene mcr-1. These results suggest that feeding an RMBD can affect the dog’s microbiota, change the frequency of certain phylogroups, and increase the shedding of diarrheagenic E. coli. Also, feeding an RMBD seemed to be linked with the fecal shedding of multidrug-resistant E. coli, including the spread of strains harboring mobilizable colistin resistance and ESBL genes. This finding is of concern for both animal and human health.

Is It Human or Animal? The Origin of Pathogenic E. coli in the Drinking Water of a Low-Income Urban Community in Bangladesh

This study aimed to investigate the origin of diverse pathotypes of E. coli, isolated from communal water sources and from the actual drinking water vessel at the point-of-drinking inside households in a low-income urban community in Arichpur, Dhaka, Bangladesh, using a polymerase chain reaction (PCR). Forty-six percent (57/125, CI 95%: 41−58) of the isolates in the point-of-drinking water and 53% (55/103, CI 95%: 45−64) of the isolates in the source water were diarrheagenic E. coli. Among the pathotypes, enterotoxigenic E. coli (ETEC) was the most common, 81% (46/57) of ETEC was found in the point-of-drinking water and 87% (48/55) was found in the communal source water. Phylogenetic group B1, which is predominant in animals, was the most frequently found isolate in both the point-of-drinking water (50%, 91/181) and in the source (50%, 89/180) water. The phylogenetic subgroup B2₃, usually of human origin, was more common in the point-of-drinking water (65%, 13/20) than in the source water (35%, 7/20). Our findings suggest that non-human mammals and birds played a vital role in fecal contamination for both the source and point-of-drinking water. Addressing human sanitation without a consideration of fecal contamination from livestock sources will not be enough to prevent drinking-water contamination and thus will persist as a greater contributor to diarrheal pathogens.

Within-host evolution versus immigration as a determinant of Escherichia coli diversity in the human gastrointestinal tract

When a human host harbors two or more strains of Escherichia coli, the second strain is more likely to be a member of the same phylogroup rather than a different phylogroup. This outcome may be the consequence of a within host evolution event or an independent immigration/establishment event. To determine the relative importance of these two events in determining E. coli diversity in a host, a collection of multiple E. coli isolates recovered from each of 67 patients undergoing colonoscopies was used. Whole genome sequence data were available for one example of every REP-fingerprint type identified in a patient. Sequence type (ST) and single-nucleotide polymorphism (SNP) analyses revealed that 83% of strains observed in the host population were a consequence of immigration/establishment events. Restricting the analysis to hosts harboring two or more strains belonging to the same phylogroup revealed that in about half of these cases, the presence of a second strain belonging to the same phylogroup was the consequence of an independent immigration/establishment event. Thus, the results of this study show that despite hosts being exposed to a diversity of E. coli via their food, factors related to the host also determine what E. coli strains succeed in establishing.

Effects of dispersal limitation in the face of intense selection via dietary intervention on the faecal microbiota of rats

Four ecological processes mediate microbial diversity: selection, whereby host factors favour the persistence of particular microbial taxa; historical contingency, where differences in the timing and order of microbial acquisition results in different communities; stochastic factors that impact community assemblages; and dispersal limitation, where the presence of particular taxa is restricted by host population structure and local environmental factors. However, few studies have explored the impact of selection through diet modification on the differences in microbial community composition arising from dispersal limitation. At weaning, the faecal microbiota of 45 rats originating from six litters, as assessed by 16S rRNA gene sequencing, was strongly correlated with an animal's litter membership. Following 14 weeks on one of three the experimental diets, the faecal microbiota of the rats were again characterized. Clear effects of diet on microbial community composition were observed. However, after 14 weeks of dietary intervention, the effect of litter membership on microbial community composition was still significant. Our results demonstrate that intense selection (diet manipulation) cannot completely eliminate differences in microbial communities that occurred as a consequence of dispersal limitation (litter membership) prior to selection. These results have clear implications for efforts that attempt to achieve positive health outcomes through diet manipulation.

A peptide identification-free, genome sequence-independent shotgun proteomics workflow for strain-level bacterial differentiation

Shotgun proteomics is an emerging tool for bacterial identification and differentiation. However, the identification of the mass spectra of peptides to genome-derived peptide sequences remains a key issue that limits the use of shotgun proteomics to bacteria with genome sequences available. In this proof-of-concept study, we report a novel bacterial fingerprinting method that enjoys the resolving power and accuracy of mass spectrometry without the burden of peptide identification (i.e. genome sequence-independent). This method uses a similarity-clustering algorithm to search for mass spectra that are derived from the same peptide and merge them into a unique consensus spectrum as the basis to generate proteomic fingerprints of bacterial isolates. In comparison to a traditional peptide identification-based shotgun proteomics workflow and a PCR-based DNA fingerprinting method targeting the repetitive extragenic palindromes elements in bacterial genomes, the novel method generated fingerprints that were richer in information and more discriminative in differentiating E. coli isolates by their animal sources. The novel method is readily deployable to any cultivable bacteria, and may be used for several fields of study such as environmental microbiology, applied microbiology, and clinical microbiology.

Escherichia coli diversity in the lower intestinal tract of humans

Previous studies examining the clonal diversity of Escherichia coli populations within humans have been based on faecal isolates. In this study E. coli were isolated from biopsies taken from the terminal ileum, ascending, transverse and descending colon, and rectum of 69 individuals. Multiple isolates from each biopsy were characterized using Rep-PCR. An average of 3.5 genotypes were recovered per host, and in hosts with two or more strains, the phylogroup membership of the second most abundant strain was significantly more likely to be the same as the dominant strain. There was no indication of a non-random distribution of E. coli phylogroups among the regions of the lower intestine. In hosts with multiple genotypes, as defined by Repetitive extragenic palindromic-PCR, genotypes were non-randomly distributed among gut regions in over half the individuals. The phylogroup membership of an individual's numerically dominant strain explained some of the variation in the extent to which strains within an individual were heterogeneously distributed, with most heterogeneity observed when the numerically dominant strain belonged to phylogroups E or F, and the least when the dominant strain belonged to phylogroup B2. The results of this study support previous studies on pigs that demonstrated faecal sampling underestimates the genotype diversity present within a host.

Host litter-associated gut dynamics affect Escherichia coli abundance and adhesion genotype in rats

The probability of detecting Escherichia coli varies between host species with different diets and body sizes. An experimental study that mimicked the effect of different carnivore body masses found that digesta transit times influence E. coli abundance. In this study, we investigated how the host's gastrointestinal dynamics affected E. coli abundance and genotype in a system that reflected an herbivorous host. Forty rats from nine litters were fed a diet high in fermentable fibre. We found a small effect of fibre concentration on the difference between the liquid and particle digesta retention times. However, the rats' litter membership explained the majority of the retention time differences (79%). In turn, we found that as the difference between liquid and particle retention times increased, E. coli faecal cell densities decreased, while the likelihood that an animal's dominant E. coli strain possessed a gene involved in adhesion (agn43) increased. Thus, this experiment revealed an unanticipated high degree of association between the hosts' litter, their gastrointestinal dynamics and the E. coli genotypes. Furthermore, by comparing our findings to previous work, we show that the presence of fermentable fibre in the diet appears to change the relationship between the host's phenotype and E. coli.

Antimicrobial resistance risk factors and characterisation of faecal E. coli isolated from healthy Labrador retrievers in the United Kingdom

Antimicrobial resistant bacteria are increasingly detected from canine samples but few studies have examined commensal isolates in healthy community dogs. We aimed to characterise faecal Escherichia coli from 73 healthy non-veterinarian-visiting and non-antimicrobial treated Labrador retrievers, recruited from dog shows in the North West United Kingdom between November 2010 and June 2011. Each enrolled dog provided one faecal sample for our study. E. coli were isolated from 72/73 (99%) faecal samples. Disc diffusion susceptibility tests were determined for a range of antimicrobials, including phenotypic extended-spectrum beta-lactamase (ESBL) and AmpC-production. PCR assay detected phylogenetic groups and resistance genes (blaCTX-M, blaSHV, blaTEM, blaOXA, blaCIT, qnr), and conjugation experiments were performed to investigate potential transfer of mobile genetic elements. Multivariable logistic regression examined potential risk factors from owner-questionnaires for the presence of antimicrobial resistant faecal E. coli. Antimicrobial resistant, multi-drug resistant (≥3 antimicrobial classes; MDR) and AmpC-producing E. coli were detected in 63%, 30% and 16% of samples, respectively. ESBL-producing E. coli was detected from only one sample and conjugation experiments found that blaCTX-M and blaCIT were transferred from commensal E. coli to a recipient strain. Most isolates were phylogenetic groups B1 and A. Group B2 isolates were associated with lower prevalence of resistance to at least one antimicrobial (P<0.001) and MDR (P<0.001). Significant at P<0.003, was the consumption of raw meat for clavulanate-amoxicillin (OR: 9.57; 95% CI: 2.0-45.7) and third generation cephalosporin resistance (3GCR) (OR: 10.9; 95% CI: 2.2-54.0). AMR E. coli were surprisingly prevalent in this group of non-antimicrobial treated and non-veterinarian-visiting dogs and consumption of raw meat was a significant risk factor for antimicrobial resistance. These findings are of concern due to the increasing popularity of raw-meat canine diets, and the potential for opportunistic infection, zoonotic transmission and transmission of antimicrobial resistant determinants from commensal isolates to potential pathogenic bacteria.

Comparative prevalence and characterization of ESBL-producing Enterobacteriaceae in dominant versus subdominant enteric flora in veal calves at slaughterhouse, France

Food-producing animals have become a growing reservoir of Extended-Spectrum Beta-Lactamase (ESBL)-producing bacteria. In cattle, veal calves are exposed to high amounts of antibiotics but ESBL prevalence data are still limited compared to other food sectors such as poultry production. Based on the investigation of 491 veal calves from different slaughtering batches at 12 abattoirs, this study shows a prevalence of 29.4% of ESBL producers in the faecal flora of veal calves in France in 2012. A variety of blaCTX-M genes was found, reflecting possible diverse pathways of dissemination in cattle. Another major conclusion is the comparison of the ESBL prevalence in the dominant versus sub-dominant Escherichia coli population of the same calves (1% and 29.4%, respectively). Also, the ESBL E. coli clones in the sub-dominant flora mostly differed from the non-ESBL dominant E. coli clones of the same calves. Of note, the distribution of blaCTX-M genes and E. coli phylogroups were similar to the ones previously found in ESBL E. coli clones from diseased calves. The hypothesis that ESBL genes may distribute more abundantly in certain backgrounds of E. coli was also discussed. In all, as recently reported in the Netherlands, these results strongly suggest a recent increase in the prevalence of ESBL carriage in French veal calves, which should be considered one of the major ESBL reservoirs in food animals.

Functional genotypes are associated with commensal Escherichia coli strain abundance within-host individuals and populations

The selective pressures that determine genotype abundance and distribution frequently vary between ecological levels. Thus, it is often unclear whether the same functional genotypes will become abundant at different levels and how selection acting at these different scales is linked. In this study, we examined whether particular functional genotypes, defined by the presence or absence of 34 genes, of commensal Escherichia coli strains were associated with within-host abundance and/or host population abundance in a wild population of 54 adult mountain brushtail possums (Trichosurus cunninghami). Our results revealed that there was a positive correlation between a strain's relative abundance within individuals and the strain's abundance in the host population. We also found that strain abundance at both ecological levels was predicted by the same group of functional genes (agn43, focH, micH47, iroN, ygiL, ompT, kspmT2 and K1) that had associated patterns of occurrence. We propose that direct selection on the same functional genes at both levels may in part be responsible for the observed correlation between the ecological levels. However, a potential link between abundance within the host and excretion rate may also contribute.

Commensal Escherichia coli strains in Guiana reveal a high genetic diversity with host-dependant population structure

We undertook a large-scale epidemiological survey of commensal Escherichia coli in Trois-Sauts, an isolated village located in the south of French Guiana where human population exchanges are restricted and source of antibiotics controlled. Stools from 162 Wayampi Amerindians and rectal swabs from 33 human associated and 198 wild animals were collected in the close proximity of the village. The prevalence of E. coli was decreasing from humans (100%) to human associated (64%) and wild (45%) animals. A clear genetic structure between these three E. coli populations was observed with human strains belonging very rarely to B2 phylogroup (3.7%), exhibiting few virulence genes and bacteriocins but being antibiotic resistant whereas wild animal strains were characterized by 46.1% of B2 phylogroup belonging, with very unique and infrequent sequence types, numerous extraintestinal genes and bacteriocins but no antibiotic resistance; the human-associated animal strains being intermediate. Furthermore, an unexpected genetic diversity was observed among the strains, as the housekeeping gene nucleotide diversity per site of the Trois-Sauts's strains was higher than the one of reference strains representative of the known species diversity. The existence of such E. coli structured phylogenetic diversity within various hosts of a single localization has never been reported.

Phylogenetic distribution of traits associated with plant colonization in Escherichia coli

Plants are increasingly considered as secondary reservoirs for commensal and pathogenic Escherichia coli strains, but the ecological and functional factors involved in this association are not clear. To address this question, we undertook a comparative approach combining phenotypic and phylogenetic analyses of E. coli isolates from crops and mammalian hosts. Phenotypic profiling revealed significant differences according to the source of isolation. Notably, isolates from plants displayed higher biofilm and extracellular matrix production and higher frequency of utilization of sucrose and the aromatic compound p-hydroxyphenylacetic acid. However, when compared with mammalian-associated strains, they reached lower growth yields on many C-sources commonly used by E. coli. Strikingly, we observed a strong association between phenotypes and E. coli phylogenetic groups. Strains belonging to phylogroup B1 were more likely to harbour traits indicative of a higher ability to colonize plants, whereas phylogroup A and B2 isolates displayed phenotypes linked to an animal-associated lifestyle. This work provides clear indications that E. coli phylogroups are specifically affected by niche-specific selective pressures, and provides an explanation on why E. coli population structures vary in natural environments, implying that different lineages in E. coli have substantially different transmission ecology.