[Distribution in different Salmonella serovars and integration sites of Salmonella paratyphi C phage SPC-P1]

To determine the prevalence of Salmonella paratyphi C phage (SPC-P1) in different Salmonella serovars and to identify the integration sites in host genome.

Based on the complete genome of SPC-P1 in S. paratyphi C RKS4594, 6 pairs of primers were designed and used to amplify the fragments of SPC-P1 in 11 S. typhi, 11 S. paratyphi A, 12 S. paratyphi B and 23 S. paratyphi C strains. At the same time, 100 complete genomes of Salmonella including 20 serovars available in National Center for Biotechnology Information (NCBI) database were downloaded and aligned by Mauve 2.3.1 to determine the prevalence of SPC-P1 in these serovars. Primers were designed according to the integration sites of SPC-P1 in the genome of RKS4594, and used to amplify ten strains having SPC-P1 in the genome. The PCR products were sequenced to investigate the integration sites of SPC-P1.

SPC-P1 was widely distributed in S.paratyphi C genome. In the study, 14 strains had all 6 fragments and 2 strains had 3-5 fragments. All the amplified fragments showed expected sizes. In contrast, in the genomes of S. typhi, S. paratyphi A and S. paratyphi B, no or only 1-2 fragments could be amplified, and the sizes were smaller than expected. The results from Mauve showed that only in the genome of S.choleraesuis, which was a close relative of S. paratyphi C, there existed an almost complete genome of SPC-P1. The insertion site of SPC-P1 in all the ten S. paratyphi C strains tested was between pgtE and yfdC genes.

SPC-P1 is a unique virulence factor of S. paratyphi C. It may play roles in the host range and pathogenicity of S.paratyphi C.