Intestine and Environment of the Chicken as Reservoirs for Extraintestinal Pathogenic Escherichia coli Strains with Zoonotic Potential

Abstract

Although research has increasingly focused on the pathogenesis of avian pathogenic Escherichia coli (APEC) infections and the "APEC pathotype" itself, little is known about the reservoirs of these bacteria. We therefore compared outbreak strains isolated from diseased chickens (n ‫؍‬ 121) with nonoutbreak strains, including fecal E. coli strains from clinically healthy chickens (n ‫؍‬ 211) and strains from their environment (n ‫؍‬ 35) by determining their virulence gene profiles, phylogenetic backgrounds, responses to chicken serum, and in vivo pathogenicities in a chicken infection model. In general, by examining 46 different virulence-associated genes we were able to distinguish the three groups of avian strains, but some specific fecal and environmental isolates had a virulence gene profile that was indistinguishable from that determined for outbreak strains. In addition, a substantial number of phylogenetic EcoR group B2 strains, which are known to include potent human and animal extraintestinal pathogenic E. coli (ExPEC) strains, were identified among the APEC strains (44.5%) as well as among the fecal E. coli strains from clinically healthy chickens (23.2%). Comparably high percentages (79.2 to 89.3%) of serum-resistant strains were identified for all three groups of strains tested, bringing into question the usefulness of this phenotype as a principal marker for extraintestinal virulence. Intratracheal infection of 5-week-old chickens corroborated the pathogenicity of a number of nonoutbreak strains. Multilocus sequence typing data revealed that most strains that were virulent in chicken infection experiments belonged to sequence types that are almost exclusively associated with extraintestinal diseases not only in birds but also in humans, like septicemia, urinary tract infection, and newborn meningitis, supporting the hypothesis that not the ecohabitat but the phylogeny of E. coli strains determines virulence. These data provide strong evidence for an avian intestinal reservoir hypothesis which could be used to develop intestinal intervention strategies. These strains pose a zoonotic risk because either they could be transferred directly from birds to humans or they could serve as a genetic pool for ExPEC strains.Extraintestinal Escherichia coli infections are among the most significant infectious diseases in production birds and result in severe losses due to mortality, production losses, and condemnations. As a clearly defined genotype of avian pathogenic E. coli (APEC) has still not been determined, the term APEC is commonly ill-defined and used for strains isolated from poultry with clinical signs of different local and systemic E. coli infections, like air sacculitis, cellulites, and septicemia (2, 10, 14). Although research has increasingly focused on the pathogenesis of APEC infections and the "APEC pathotype," we have little knowledge about the reservoir of these bacteria, considerably hampering disease control. Recent investigations comparing E. coli strains isolated from internal organs of pou...

Diagnostic Strategy for Identifying Avian Pathogenic Escherichia coli Based on Four Patterns of Virulence Genes

“…Pathogenic I isolates did not differ from pathogenic L isolates when considering the number of dead chicks. It is not surprising to observe that some I isolates were virulent, since it is well established that the chicken intestine is the main reservoir of pathogenic strains (4,25). Notably, 47 strains isolated from lesions were nonpathogenic.…”

Multi-locus sequence typing and plasmid profile characterization of avian pathogenicEscherichia coliassociated with increased mortality in free-range layer flocks

“…However, if the hypothesis that typhlitis due to H. meleagridis/H. gallinarium represents a predisposing factor for subsequent infection with E. coli is correct, a multitude of STs are expected to IncFIB 140 40 IncFIB 117 40 IncFIB 140 40 IncFIB 117 41 IncFIB 140 42 IncFIB E 2 117 41 IncFIB 140 42 IncFIB 140 42 IncFIB 140 42 IncFIB 140 42 IncFIB 140 42 IncFIB 117 43 IncFIB be associated with subsequent colibacillosis due to the diversity of potential pathogenic E. coli in the intestine (Ewers et al, 2009). However, it cannot be excluded that specific clones might develop in accordance with the ''mix and match'' theory (Mokady et al, 2005).…”

Sequencing and Functional Annotation of Avian Pathogenic Escherichia coli Serogroup O78 Strains Reveal the Evolution of E. coli Lineages Pathogenic for Poultry via Distinct Mechanisms

“…This is further evident from multilocus sequence typing and the extensive conservation of virulence-associated loci in APEC and human ExPEC (4)(5)(6)(7)(8)(9)(10)(11)(12)(13) and indicates that APEC found in poultry may pose a threat of zoonosis. Indeed, a subset of APEC ST95 serogroup O18 isolates produced pathology comparable to that of human neonatal meningitis-associated E. coli (NMEC) in a rat model of meningitis, and reciprocally, NMEC O18 isolates caused systemic disease in chickens (14).…”