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

Abstract

Avian pathogenic Escherichia coli strains originating from 10 free-range layer flocks were characterized by multi-locus sequence typing and plasmid profile analysis to investigate their phylogenetic relationship and diversity, respectively. In addition to colibacillosis, all flocks tested positive for antibodies against avian metapneumovirus (aMPV) during production, and six of the flocks were concurrently affected by histomonosis. Accumulated average mortality for flocks concurrently affected by colibacillosis and histomonosis made up 17.4%, while the average mortality for E. coli-infected flocks was 16.5%. A total of eight different sequence types (STs) and 47 different plasmid profiles were demonstrated among the E. coli isolates. Within each flock between one and four different STs and between three and 13 different plasmid profiles were demonstrated. A statistical significant difference in STs and plasmid profile diversity of the population of E. coli was not demonstrated between flocks affected by histomonosis compared with histomonosis-free flocks. Only minor clonal diversity was demonstrated for each flock, and in all but one flock colibacillosis started before antibodies against aMPV were detected. All isolates, except two, carried plasmids greater than 100 kb, but only a single plasmid replicon type, IncFIB, was demonstrated, suggesting plasmids representing this type might represent a common pathogenicity factor for the different STs of E. coli. Within each flock a clonal tendency was observed, indicating that only certain clones of E. coli possess a significant pathogenic potential. These clones act as primary rather than secondary pathogens, resulting in colibacillosis without predisposing factors, including histomonosis and aMPV.

Molecular typing of avian pathogenicEscherichia colicolonies originating from outbreaks ofE. coliperitonitis syndrome in chicken flocks

“…E. coli infections are often considered opportunistic whenever the bacteria of concern display great genetic variation. Limited genetic diversity of E. coli bacteria has been reported associated with acute haemorrhagic septicaemia in turkeys (Olsen et al, 2011a), in E. coli septicaemia lesions following cellulitis in chickens (Jeffrey et al, 2002) and in EPS cases found in free-range layer flocks (Olsen et al, 2011b). Also in the present study, limited genetic variation amongst E. coli colonies from bone marrow of laying hens with EPS was found.…”

“…However, four PFGE types shared ST 95. In the present study, 12 STs were detected, while Olsen et al (2011b) found eight STs in 10 flocks of free-range layers with EPS. Both studies revealed five STs in common (ST 23,ST 57,ST 95,ST 117 and ST 141).…”

“…In some cases, however, E. coli was obtained from well-defined disease and lesions. Examples of such research are a study performed by Olsen et al (2011a) in which the clonality and virulence traits of E. coli associated with haemorrhagic septicaemia in turkeys was examined, studies concerning avian cellulitis (Singer et al, 2000;Jeffrey et al, 2002) and research on MLST and plasmid profile characterization of APEC associated with increased mortality in layers (Olsen et al, 2011b). In the present study we examined E. coli bacteria that also originated from welldefined disease outbreaks and lesions; that is, outbreaks of EPS in laying hens and in which only E. coli bacteria obtained from bone marrow were typed using PFGE and MLST.…”

“…Only Olsen and coworkers genotyped E. coli bacteria obtained from laying hens with EPS (Olsen et al, 2011b). In the present study, therefore, the genetic relatedness of E. coli colonies obtained from the bone marrow of birds with EPS was studied using pulsedfield gel electrophoresis (PFGE).…”

In silico phylogenetic and virulence gene profile analyses of avian pathogenic Escherichia coli genome sequences

“…All strains isolated from wild pigeon and parrot were pathogenic, while there were both pathogenic and nonpathogenic strains isolated from chickens (MLST database). The ST117 (SEPT362 -septicemic) is frequently found in APEC strains, in fact, this ST was the most prevalent type detected in two different studies that determined ST for E. coli isolates from several Danish broiler breeders and layer farms (Gregersen et al 2010, Olsen et al 2011) and in the MLST database. This ST is also associated to human urinary tract infections (UTI) (Wu et al 2012).…”