Researchers Investigate <em>E. coli</em> Pathogenicity

CHINA - The findings in a recently published paper may lead the way to developing intestinal preventive strategies.

1 September 2010

4 minute read

Jianjun Dai from Nanjing Agricultural University and co-authors there and at the Free University in Berlin, Germany, have published a paper in BMC Microbiology on the pathogenicity factors in avian pathogenic Escherichia coli (APEC).

Extra-intestinal pathogenic E. coli (ExPEC) represent a phylogenetically diverse group of bacteria which are implicated in a large range of infections in humans and animals, according to the authors. Although sub-groups 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 sub-set of strains or a distinct pathotype.

They made use of suppression subtractive hybridisation 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 that may complete the currently existing model of APEC pathogenicity and further elucidate the position of this avian pathotype within the whole ExPEC group.

Results

Twenty-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 base pairs (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.

Conclusions

Dai and co-authors say that thy 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 per cent 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.

The 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, conclude Dai and co-authors.

Reference

Dai J., S. Wang, D. Guerlebeck, C. Laturnus, S. Guenther, Z. Shi, C. Lu and C. Ewers. 2010. Suppression subtractive hybridization identifies an autotransporter adhesin gene of E. coli IMT5155 specifically associated with avian pathogenic Escherichia coli (APEC). BMC Microbiology, 10:236. doi:10.1186/1471-2180-10-236.