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Appl. Environ. Microbiol. doi:10.1128/AEM.02634-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Evolution of the iss gene in Escherichia coli

Department of Veterinary and Biomedical Sciences, University of Minnesota, 1971 Commonwealth Ave., 205 Veterinary Science, Saint Paul, MN 55108; Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, 1802 Elwood Drive, VMRI #2, Ames, IA 50011

^* To whom correspondence should be addressed. Email: joh04207{at}umn.edu.

	Abstract

The increased serum survival gene, iss, has long been recognized for its role in extraintestinal pathogenic Escherichia coli (ExPEC) virulence. iss has been identified as a distinguishing trait of avian ExPEC but not human ExPEC. This gene has been localized to large virulence plasmids and shares strong similarities with the bor gene from bacteriophage . Here, we demonstrate that three alleles of iss occur among E. coli that appear to have evolved from a common bor precursor. In addition to the occurrence of iss on ColV/BM virulence plasmids, at least two iss alleles occur within the E. coli chromosome. One of these alleles (designated type 3) was found to occur in the genomes of all currently sequenced ExPEC on a similar prophage element also harboring the Sit iron and manganese transport system. When the prevalence of the three iss types was examined among 487 E. coli isolates, iss type 3 was found to occur at a high frequency among ExPEC, irrespective of host source. The plasmid-borne iss allele (designated type 1) was highly prevalent among APEC and neonatal meningitis-associated E. coli but not among uropathogenic E. coli. This study demonstrates the evolution of iss in E. coli and provides an additional tool for discriminating among E. coli pathotypes through differentiation of the three iss allele types and bor.