PATHOGENICITY ISLAND EVALUATION IN ESCHERICHIA-COLI K1 BY CROSSING WITH LABORATORY STRAIN K-12

In bacterial pathogens, strain-specific chromosomal segments often con tain genes encoding strain-specific traits, and because these genes of ten appear to be dedicated to pathogenic interactions with eucaryotic hosts, the segments containing them may be considered so-called pathog enicity island (G. Blum, M. Ott, A. Lischewski, A. Ritter, H. Imrich, H. Tschape, and J. Hacker, Infect. Immune. 62:606-614, 1994). We evalu ated the contribution to pathogenesis of a recently identified strain- specific chromosomal segment from an Escherichia coli K1 mammalian-new born sepsis strain: transfer of E. coli K-12 DNA sequences near 64 min , by P1 transduction, into K1 strain RS218 resulted in an RS218-K-12 c himera that (i) contained a shortened NotI restriction fragment (relat ive to wild-type RS218) encompassing the 64-min region; (ii) lacked in vasiveness in newborn rats; and (iii) grew in vitro, both rich and min imal laboratory media, indistinguishably from strain RS218. In additio n, genomic DNA from the chimera failed to hybridize with sequences of the K1 capsule genes from strain RS218, suggesting that the chromosoma l segment near 64 min which was lost contained these sequences and ind eed contained K1-specific virulence genes. Transfer of K-12 sequences resulting in deletion of E. coli pathogen-specific chromosomal segment s may afford an general method of detecting genes encoding virulence a nd/or other distinguishing traits.