Relationship between phylogenetic groups of Escherichia coli and Pathogenicity among Isolates from chickens with Colibacillosis and healthy chickens

Abstract

Avian pathogenic Escherichia coli (APEC) is closely related to extraintestinal pathogenic E. coli, which are frequently assigned to specific phylogenetic groups (phylogroups). Therefore, we investigated the association between phylogroups of E. coli isolates and those recovered from commercial broiler and layer chickens with colibacillosis. We used 104 E. coli isolates from chickens with colibacillosis (hereafter referred to as "colibacillosis-related isolates"), 56 E. coli isolates obtained from fecal samples of clinically healthy broiler chickens, and 58 isolates obtained from environmental samples of layer chicken housing facilities where clinically healthy layer chickens were reared (hereafter referred to as "healthy chicken-related isolates"). The prevalence of phylogroup F among colibacillosis-related isolates was significantly (P < 0.05) higher than that among healthy chicken-related isolates, while phylogroups A and B1 were more frequently distributed in healthy chicken-related isolates. Fifty-seven (87%) of 65 colibacillosis-related isolates belonging to phylogroup F were defined as APEC based on the presence of virulence-associated genes according to a previously established criterion. In contrast, none of the healthy chicken-related isolates were defined as APEC. As evidenced by the chicken embryo lethality assay, 87 of the 92 healthy chicken-related isolates tested had embryo lethality rates of <30% and were considered avirulent, whereas 59 of the 104 colibacillosis-related isolates were considered virulent. Nonetheless, among isolates exhibiting embryo lethality rates of <30%, the mean lethality rate of embryos inoculated with colibacillosis-related isolates was significantly higher than that of embryos inoculated with healthy chicken-related isolates. These observations suggest that phylogroup F predicts colibacillosis among E. coli strains with virulence-associated genes.

Keywords: Escherichia coli; chicken; colibacillosis; phylogroup; virulence.

Figure 1

Prevalence of virulence-associated genes among E. coli isolates from layer chickens with colibacillosis (a), broiler chickens with colibacillosis (b), environmental samples of layer housing facilities obtained while the layer chickens were clinically healthy (c), and healthy broiler chickens (d). Numbers on the x-axis represent those detected among the following 5 genes/groups: (1) kpsMT II; (2) iss; (3) tsh; (4) one of the 5 genes sfa, foc, papA, papC, and papEF; and (5) one of the 2 genes iutA and fyuA. Isolates defined as avian pathogenic Escherichia coli (see Materials and Methods) are indicated by horizontal lines. Phylogroup: A, red; B1, orange; B2, gray; C, yellow; D, cyan; E, green; F, dark blue.

Figure 2

Embryo lethality assay inoculated with E. coli isolates from layer chickens with colibacillosis (a), broiler chickens with colibacillosis (b), environmental samples of layer housing facilities obtained while the layer chickens were clinically healthy (c), and healthy broiler chickens (d). The number of dead chicken embryos 2 d postinoculation is indicated on the x-axis. Isolates considered virulent (see Materials and Methods) are indicated by horizontal lines. Phylogroup: A, red; B1, orange; B2, gray; C, yellow; D, cyan; E, green; F, dark blue.