Molecular cloning and characterization of chromosomal virulence region kcpA of Shigella flexneri

In Shigella flexneri, in addition to several well-recognized plasmid-borne virulence loci, at least three genetic loci implicated in pathogenesis have been recognized on the chromosome. To understand more about the pathogenesis of bacillary dysentery at a molecular level, the genetically recognized but previously unidentified KcpA region (one of the chromosomal regions near purE) was cloned and sequenced. A single translatable open reading frame encoding a 12310 Dalton protein corresponding to the minicell product was found. Immunofluorescence microscopy, as well as optical and electron microscopic comparison of tissue-cultured cells and guinea-pigs' eyes infected with wild-type or kcpA mutant bacteria, revealed that the kcpA product is required by invading bacteria for spread into adjacent cells.