Abstract
BackgroundExtraintestinal pathogenic E. coli (ExPEC) represent a phylogenetically diverse group of bacteria which are implicated in a large range of infections in humans and animals. Although subgroups of different ExPEC pathotypes, including uropathogenic, newborn meningitis causing, and avian pathogenic E. coli (APEC) share a number of virulence features, there still might be factors specifically contributing to the pathogenesis of a certain subset of strains or a distinct pathotype. Thus, we made use of suppression subtractive hybridization and compared APEC strain IMT5155 (O2:K1:H5; sequence type complex 95) with human uropathogenic E. coli strain CFT073 (O6:K2:H5; sequence type complex 73) to identify factors which may complete the currently existing model of APEC pathogenicity and further elucidate the position of this avian pathoype within the whole ExPEC group.ResultsTwenty-eight different genomic loci were identified, which are present in IMT5155 but not in CFT073. One of these loci contained a gene encoding a putative autotransporter adhesin. The open reading frame of the gene spans a 3,498 bp region leading to a putative 124-kDa adhesive protein. A specific antibody was raised against this protein and expression of the adhesin was shown under laboratory conditions. Adherence and adherence inhibition assays demonstrated a role for the corresponding protein in adhesion to DF-1 chicken fibroblasts. Sequence analyses revealed that the flanking regions of the chromosomally located gene contained sequences of mobile genetic elements, indicating a probable spread among different strains by horizontal gene transfer. In accordance with this hypothesis, the adhesin was found to be present not only in different phylogenetic groups of extraintestinal pathogenic but also of commensal E. coli strains, yielding a significant association with strains of avian origin.ConclusionsWe identified a chromosomally located autotransporter gene in a highly virulent APEC strain which confers increased adherence of a non-fimbriated E. coli K-12 strain to a chicken fibroblast cell line. Even though flanked by mobile genetic elements and three different genetic regions upstream of the gene, most probably indicating horizontal gene transfer events, the adhesin gene was significantly linked with strains of avian origin. Due to the nucleotide sequence similarity of 98% to a recently published adhesin-related gene, located on plasmid pAPEC-O1-ColBM, the name aatA (APEC autotransporter adhesin A) was adopted from that study.Our data substantiate that AatA might not only be of relevance in APEC pathogenicity but also in facilitating their reservoir life style in the chicken intestine, which might pave the way for future intestinal preventive strategies.
Highlights
Extraintestinal pathogenic E. coli (ExPEC) represent a phylogenetically diverse group of bacteria which are implicated in a large range of infections in humans and animals
Identification of genes present in APEC strain IMT5155 but absent in human UPEC strain CFT073 The aim of the work presented here was to identify new potential virulence genes specific for avian pathogenic E. coli (APEC) strains, which might be important in the pathogenesis of systemic infections in poultry and helpful in delineating this pathotype from other ExPEC pathotypes
To explore the specificity of these gene fragments for APEC strain IMT5155, PCR amplicons were transferred to a nylon membrane and southern hybridization analysis was performed with labelled genomic DNA of UPEC strain CFT073 and K12 strain MG1655, respectively
Summary
Extraintestinal pathogenic E. coli (ExPEC) represent a phylogenetically diverse group of bacteria which are implicated in a large range of infections in humans and animals. Escherichia coli typically colonize the mammalian and avian gastrointestinal tract and other mucosal surfaces While many of these strains are commensal, certain pathogenic strains have the ability to cause severe diseases [1]. Extraintestinal pathogenic E. coli (ExPEC) are a group of strains that are implicated in a large range of infections in humans and animals, such as neonatal meningitis, urinary tract infection, intra abdominal infection, pneumonia, osteomyelitis and septicaemia [2,3,4]. APEC enter and colonize the avian respiratory tract by inhalation of fecal dust leading to localized infections such as airsacculitis and pneumonia In certain cases, they spread into various internal organs typically causing pericarditis, perihepatitis, peritonitis, salpingitis and other extraintestinal diseases. Systemic infection of poultry is characterized in its acute form by septicemia, commonly resulting in sudden death [3,6]
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