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Characterization of the flexible genome complement of the commensal Escherichia coli strain A0 34/86 (O83 : K24 : H31)

¹ Unité de Génomique des Microorganismes Pathogènes and CNRS URA 2171, Institut Pasteur, 28 Rue du Dr. Roux, 75724 Paris, France
² Laboratory of Molecular Biology of Bacterial Pathogens, Institute of Microbiology of the Czech Academy of Sciences, Videnska 1083, 142 20 Prague 4, Czech Republic
³ Institut für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany
⁴ Research Institute of Veterinary Medicine, Hlinkova 1/A, 040 01 Kosice, Slovakia
⁵ Plate-Forme 4 – Intégration et Analyse Génomique, Institut Pasteur, 28 Rue du Dr. Roux, 75724 Paris, France

Correspondence
Carmen Buchrieser
cbuch{at}pasteur.fr

Colonization by the commensal Escherichia coli strain A0 34/86 (O83 : K24 : H31) has proved to be safe and efficient in the prophylaxis and treatment of nosocomial infections and diarrhoea of preterm and newborn infants in Czech paediatric clinics over the past three decades. In searching for traits contributing to this beneficial effect related to the gut colonization capacity of the strain, the authors have analysed its genome by DNA–DNA hybridization to E. coli K-12 (MG1655) genomic DNA arrays and to ‘Pathoarrays’, as well as by multiplex PCR, bacterial artificial chromosome (BAC) library cloning and shotgun sequencing. Four hundred and ten E. coli K-12 ORFs were absent from A0 34/86, while 72 out of 456 genes associated with pathogenicity islands of E. coli and Shigella were also detected in E. coli A0 34/86. Furthermore, extraintestinal pathogenic E. coli-related genes involved in iron uptake and adhesion were detected by multiplex PCR, and genes encoding the HlyA and cytotoxic necrotizing factor toxins, together with 21 genes of the uropathogenic E. coli 536 pathogenicity island II, were identified by analysis of 2304 shotgun and 1344 BAC clone sequences of A0 34/86 DNA. Multiple sequence comparisons identified 31 kb of DNA specific for E. coli A0 34/86; some of the genes carried by this DNA may prove to be implicated in the colonization capacity of the strain, enabling it to outcompete pathogens. Among 100 examined BAC clones roughly covering the A0 34/86 genome, one reproducibly conferred on the laboratory strain DH10B an enhanced capacity to persist in the intestine of newborn piglets. Sequencing revealed that this BAC clone carried gene clusters encoding gluconate and mannonate metabolism, adhesion (fim), invasion (ibe) and restriction/modification functions. Hence, the genome of this clinically safe and highly efficient colonizer strain appears to harbour many ‘virulence-associated’ genes. These results highlight the thin line between bacterial ‘virulence’ and ‘fitness' or ‘colonization’ factors, and question the definition of enterobacterial virulence factors.

The GenBank/EMBL/DDBJ accession number for the sequence of the completely sequenced BAC insert (C4/1) is AJ829704.

A list of non-detectable ORFs of E. coli strain MG1655 in strain Colinfant in the order in which the ORFs appear in the MG1655 chromosome, together with a list of detectable virulence-associated or PAI-localized genes of pathogenic E. coli may be found in Supplementary Table S1 with the online version of this paper at http://mic.sgmjournals.org. A list of genes of the flexible E. coli genome complement identified in E. coli strain A0 34/86 by the combination of DNA array hybridization, Multiplex PCR and partial genome sequencing may be found in Supplementary Table S2.

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