Complete DNA Sequence and Comparative Analysis of the 50-Kilobase Virulence Plasmid of Salmonella enterica Serovar Choleraesuis

Abstract

The complete nucleotide sequence of pKDSC50, a large virulence plasmid from Salmonella enterica serovar Choleraesuis strain RF-1, has been determined. We identified 48 of the open reading frames (ORFs) encoded by the 49,503-bp molecule. pKDSC50 encodes a known virulence-associated operon, the spv operon, which is composed of genes essential for systemic infection by nontyphoidal Salmonella. Analysis of the genetic organization of pKDSC50 suggests that the plasmid is composed of several virulence-associated genes, which include the spvRABCD genes, plasmid replication and maintenance genes, and one insertion sequence element. A second virulence-associated region including the pef (plasmid-encoded fimbria) operon and rck (resistance to complement killing) gene, which has been identified on the virulence plasmid of S. enterica serovar Typhimurium, was absent. Two different replicon regions, similar to the RepFIIA and RepFIB replicons, were found. Both showed high similarity to those of the pO157 plasmid of enterohemorrhagic Escherichia coli O157:H7 and the enteropathogenic E. coli ( Plasmid-encoded gene products are required for full expression of virulence in many enteropathogenic bacteria, including those of the genera Shigella (53, 54) and Yersina (17,20), as well as Salmonella (12,33,35,47,56). Nontyphoidal Salmonella serovars are important agents of gastroenteritis and can cause systemic infection, such as bacteremia (septicemia), in animals and humans. Many of these serotypes typically carry large plasmids which are essential to the production of systemic infection in animal models (21,23). Although the virulence plasmids of these Salmonella strains are variable in size, ranging from 50 to 94 kb, their distribution is dependent on the serotype. For example, S. enterica serovar Choleraesuis, S. enterica serovar Enteritidis, S. enterica serovar Dublin, S. enterica serovars Gallinarum and Pullorum, and S. enterica serovar Typhimurium harbor the 50-, 60-, 80-, 90-, and 94-kb virulence plasmids, respectively.Strains of serovar Typhimurium cured of the virulence plasmid are strongly attenuated in their subsequent spreading infection to the mesenteric lymph nodes, spleen, and liver (23), while the presence of the virulence plasmid of Salmonella does not appear to be required for bacterial adherence to and invasion of cultured eukaryotic cells or for colonization of the cecum or invasion of Peyer's patches in the mouse (24, 42). All of these virulence plasmids contain a highly conserved 8-kb region, which contains the spv (Salmonella plasmid virulence) locus that can confer complete virulence on a strain of serovar Typhimurium cured of the plasmid (25).The spv region consists of spvR, a gene that encodes a transcriptional factor of the LysR family, and the spvABCD operon of structural genes (1,2,22,25,37). The spv operon is required for the systemic phase of disease in specific hosts, i.e., serovar Choleraesuis in pigs (15), serovar Dublin in cattle (39, 61), serovars Gallinarum and Pullorum in fowl (5, 6), and serova...

Isolation of Salmonella enterica serotype choleraesuis resistant to ceftriaxone and ciprofloxacin

“…The 49,503-bp pSCV contained 48 ORFs (43,77), and the 93,939-bp pSTV contained 108 ORFs molecules (96). Comparison of the two plasmids reveals that they are closely related (37,38).…”

“…b DNA sequence differs from that of pSTV (77 terial load in the vicinity of the epithelial cell lining. The pef operon is a 7-kb region containing genes for plasmid-encoded fimbriae (57).…”

“…It has been documented that the pef fimbriae mediate bacterial adhesion to murine intestinal epithelium, resulting in fluid accumulation in the gut (17). pSCV has a deletion in the region behind pefD (37), and pSEV has sequence variations in orf5 and orf6 (77). These deletions and variations of orf5, orf6, and rck may be associated with host adaptation in Salmonella.…”

Association of a Regulatory Gene, slyA with a Mouse Virulence of Salmonella Serovar Choleraesuis

“…We have sequenced ORF and upstream region of slyA of several serovars of Salmonella, and found that all of the serovars so far examined use the sequence TTG as initiation codon of slyA, and the nucleotide sequences of this region were highly conserved (14). In our study of Salmonella virulence, S. serovar Choleraesuis has been mainly used (1,11,13,18), because this serovar shows a high tendency to cause systemic salmonellosis to human and swine compared with S. serovar Typhimurium (2,25), and the genes responsible for systemic salmonellosis are expected to be studied in simpler system by using this serovar. In this context the function of slyA in S. serovar Choleraesuis has been investigated in relation to our previous and ongoing studies on the pathogenesis of this serovar.…”

“…For the full expression of the Salmonella virulence, many classes of virulence genes such as inv genes (7), pag genes (10), and plasmid-encoded spv genes (9,11) are required. Among them regulatory genes are of highest importance for the timely expression of the virulence genes to adapt to the environmental changes during the infection process.…”