Abstract
BackgroundExtra-intestinal pathogenic E. coli (ExPEC), including Avian Pathogenic E. coli (APEC), are very diverse. They cause a complex of diseases in Human, animals, and birds. Even though large plasmids are often associated with the virulence of ExPEC, their characterization is still in its infancy.Methodology/Principal FindingsWe fully sequenced and analyzed the large plasmid pAPEC-1 (103,275-bp) associated with the APEC strain χ7122, from worldwide serogroup O78∶K80∶H9. A putative virulence region spanning an 80-kb region of pAPEC-1 possesses four iron acquisition systems (iutA iucABCD, sitABCD, iroBCDN, and temperature-sensitive hemagglutinin tsh), a colicin V operon, increasing serum sensitivity iss, ompT, hlyF, and etsABC. Thirty three ORFs in pAPEC-1 are identified as insertion sequences (ISs) that belong to nine families with diverse origins. The full length of the transfer region in pAPEC-1 (11 kb) is shorter compared to the tra region of other sequenced F plasmids; the absence of some tra genes in pAPEC-1 affects its self-transferability, and the conjugative function of the plasmid was effective only in the presence of other plasmids. Two-replicon systems, repFIIA-repFIC and repFIB, and two post-segregational systems, srnB and hok/sok, are also present in the sequence of pAPEC-1. The comparison of the pAPEC-1 sequence with the two available plasmid sequences reveals more gene loss and reorganization than previously appreciated. The presence of pAPEC-1-associated genes is assessed in human ExPEC by PCR. Many patterns of association between genes are found.Conclusions/SignificanceThe pathotype typical of pAPEC-1 was present in some human strains, which indicates a horizontal transfer between strains and the zoonotic risk of APEC strains. ColV plasmids could have common virulence genes that could be acquired by transposition, without sharing genes of plasmid function.
Highlights
Plasmids are influential factors in the pathogenesis and evolution of bacteria [1]
Of the 163 open reading frames (ORFs), 31 genes (19%) encode proteins similar to known and putative virulence genes (Table S2), 26 (15.95%) encode proteins involved in plasmid functions (Table S3), 33 (20.24%) are similar to insertion sequence genes (Table S4), 27 (16.6%) are predicted proteins conserved in other species, and 46 genes (28.22%) are predicted proteins with no similarity to proteins in public databases
All of the ORFs assigned to putative transfer conjugative functions are located within an 11 kb region of the pAPEC-1 plasmid, referred to as the tra cluster (Fig. 2)
Summary
Plasmids are influential factors in the pathogenesis and evolution of bacteria [1]. Their ability to transfer between species is a way for plasmids to acquire new genes or target new hosts. We (i) present and analyze the full sequence of the plasmid pAPEC-1 of APEC strain x7122 (O78:K80:H9), (ii) investigated the pAPEC-1 conjugal transfer mechanism and (iii) determine the prevalence of pAPEC-1associated virulence genes in human ExPEC and their phylogenetic relationship.
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