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Infection and Immunity, August 2008, p. 3539-3549, Vol. 76, No. 8
0019-9567/08/$08.00+0     doi:10.1128/IAI.00455-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Specific Roles of the iroBCDEN Genes in Virulence of an Avian Pathogenic Escherichia coli O78 Strain and in Production of Salmochelins{triangledown}

Mélissa Caza, François Lépine, Sylvain Milot, and Charles M. Dozois*

INRS-Institut Armand-Frappier, Laval, Québec, Canada

Received 12 April 2008/ Returned for modification 16 May 2008/ Accepted 30 May 2008

Avian pathogenic Escherichia coli (APEC) strains are a subset of extraintestinal pathogenic E. coli (ExPEC) strains associated with respiratory infections and septicemia in poultry. The iroBCDEN genes encode the salmochelin siderophore system present in Salmonella enterica and some ExPEC strains. Roles of the iro genes for virulence in chickens and production of salmochelins were assessed by introducing plasmids carrying different combinations of iro genes into an attenuated salmochelin- and aerobactin-negative mutant of O78 strain {chi}7122. Complementation with the iroBCDEN genes resulted in a regaining of virulence, whereas the absence of iroC, iroDE, or iroN abrogated restoration of virulence. The iroE gene was not required for virulence, since introduction of iroBCDN restored the capacity to cause lesions and colonize extraintestinal tissues. Prevalence studies indicated that iro sequences were associated with virulent APEC strains. Liquid chromatography-mass spectrometry analysis of supernatants of APEC {chi}7122 and the complemented mutants indicated that (i) for {chi}7122, salmochelins comprised 14 to 27% of the siderophores present in iron-limited medium or infected tissues; (ii) complementation of the mutant with the iro locus increased levels of glucosylated dimers (S1 and S5) and monomer (SX) compared to APEC strain {chi}7122; (iii) the iroDE genes were important for generation of S1, S5, and SX; (iv) iroC was required for export of salmochelin trimers and dimers; and (v) iroB was required for generation of salmochelins. Overall, efficient glucosylation (IroB), transport (IroC and IroN), and processing (IroD and IroE) of salmochelins are required for APEC virulence, although IroE appears to serve an ancillary role.

* Corresponding author. Mailing address: INRS-Institut Armand-Frappier, 531 Boul. des Prairies, Laval, Québec, Canada H7V 1B7. Phone: (450) 687-5010, ext. 4221. Fax: (450) 686-5501. E-mail: charles.dozois{at}iaf.inrs.ca

{triangledown} Published ahead of print on 9 June 2008.

Editor: A. J. Bäumler

Infection and Immunity, August 2008, p. 3539-3549, Vol. 76, No. 8
0019-9567/08/$08.00+0     doi:10.1128/IAI.00455-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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