In the first steps of Salmonella pathogenesis (cell invasion, survival in macrophages) beside the role of several chromosomal virulence gene clusters, an important role is also assigned to the serovar specific plasmids. This paper intends to review these serovar specific virulence plasmids and their genes, based on the available literature and on the authors' own experience. First, it should be known that these large (50-90 kb) virulence plasmids are characteristic only to some serovars (S. Typhimurium, S. Enteritidis, S. Gallinarum, and S. Dublin), while other serovars (S. Hadar, S. Infantis) may also possess plasmids of similar size but without known virulence genes. The common trait of Salmonella virulence plasmids (psV) is the presence of the "virulence region" encoding spvRABC genes, which may play an important role in the propagation and survival of Salmonella in the parenchymal organs and in the reticuloendothelial system of the host. A further virulence linked group of genes is called "plasmid encoded fimbriae" (pef) operon most likely playing a role in the intestinal adhesion and host specificity. Another gene governs the resistance to complement killing (rck), and is, therefore responsible for bacterial survival in the serum, due to the outer membrane protein encoded by this gene. Finally, antibiotic resistance may occasionally be encoded by genes of psV providing further selection advantage to the bacteria. Due to the wide scale use of live attenuated vaccines against salmonellosis of poultry (and swine), the serovar specific virulence plasmids receives increased attention as undesired components of the vaccine strains. With this in mind, the authors performed experiments on the removal of the virulence plasmid of a S. Enteritidis strain. The first trials using ethidium bromide treatment have failed, but a transposon based elimination system, newly established by them has been successful. Results of the in vitro (cultured cell) and in vivo (day old chick) infection experiments indicated that the virulence traits of the plasmidless mutants of S. Enteritidis and of a S. Typhimurium strain have only been slightly reduced. These results are concordant with the fact that some wide spread Salmonella serovars exist without the virulence plasmid. Based on the literature data and on the experimental results produced here, it can be concluded that the role of serovar specific plasmids should be more cautiously assessed in the future, and this estimation should be strictly related to the tested strain and to the used model system.
|Number of pages||13|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - dec. 1 2007|
ASJC Scopus subject areas