Further search for virulence factors encoded by Salmonella serovar-specific plasmids.

The so called Salmonella virulence plasmids which are specifically prevalent among some of the S. enterica serovars were shown to contribute only marginally to the virulence make-up of salmonella, which is in contrast to Shigella and Yersinia spp. The experiments reported in this paper failed to find encoded plasmid factors which contribute to serum resistance, surface antigens, immunoinsufficiency or to up-regulation of chromosomally encoded factors such as toxins, surface antigens etc. Taking into consideration the rare prevalence of these plasmids among S. enterica but their common occurrence among a few of its serovars, their virulence implication remains an enigma.