Alterations in the pathogenicity of Escherichia coli K-12 after transfer of plasmid and chromosomal genes from Shigella flexneri

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Abstract
A 140 megadalton plasmid (pWR110), previously associated with virulence in S. flexneri, was transferred to E. coli K-12. Segments of S. flexneri chromosomal material were then transferred to the plasmid-bearing K-12 strains. The virulence of these transconjugant hybrids was assessed in the HeLa [human cervical carcinoma] cell model, in ligated rabbit ileal loops or in the Sereny test. A K-12 strain which harbored only pWR110 invaded HeLa cells produced minimal lesions in the rabbit ileal mucosa and was negative in the Sereny test. Plasmid-containing K-12 hybrids which had incorporated various Shigella chromosomal regions gave differential reactions in the rabbit ileal loops and in the Sereny test. Analysis of these transconjugants indicated that 3 regions were linked with virulent phenotypes. These included the his region (when the genes responsible for O-antigen synthesis were cotransferred) and the kcp locus (linked to the lac-gal region). Either of these chromosomal regions was sufficient to allow invasion of the rabbit ileal mucosa. In addition to both of these regions, another Shigella chromosomal segment linked to the arg and mti loci was necessary for fluid production in the rabbit ileal loop and for a positive Sereny reaction. Thus, derivatives of an E. coli K-12 strain, constructed by the stepwise conjugal transfer of a large plasmid and 3 chromosomal segments from S. flexneri, appeared to contain the necessary determinants for full pathogenicity in a variety of laboratory models.