GENETIC-MAP OF THE VIRULENCE PLASMID OF SALMONELLA-ENTERITIDIS AND NUCLEOTIDE-SEQUENCE OF ITS REPLICONS

Partial sequencing of a genomic library of the virulence plasmid of Sa lmonella enteritidis has been used to localize in the restriction map of this plasmid the genetic loci already described in other Salmonella plasmids. The comparison of the vestigial tla region with the corresp onding genes in the F plasmid allowed us to define the extent of the d eletions that the S. enteritidis plasmid should have suffered. The put ative replicons of the plasmid, repB and repC, were isolated and both proved to be functional in Escherichia coli, but repC was segregationa lly unstable. The nucleotide sequence of repB showed the typical organ ization of RepFIIA replicons, although the similarity was lower than u sual in this group of replicons. The highest homology was found with t he replicon of the virulence plasmid pYVe439-80 from Yersinia enteroco litica (72.5%). Replicon repC also showed a maximum identity of 72.6% with known replicons, namely the RepFIB of pCo1V-K30 and P307, both vi rulence plasmids isolated from E. coli. We conclude that the S. enteri tidis plasmid could arise from the S. typhimurium plasmid through dele tions, and that they are evolutionary distant from other IncFI and Inc FII plasmids.