Draft genome sequences of Salmonella Oslo isolated from seafood and its laboratory generated auxotrophic mutant

Phenotypic characterization of auxotrophic mutant of nontyphoidal Salmonella and determination of its cytotoxicity, tumor inhibiting cytokine gene expression in cell line models

An auxotrophic mutant of nontyphoidal Salmonella (NTS) strain (Salmonella Oslo) was phenotypically characterized in this study. The characterization was based on phenotype, morphology, motility, biofilm forming ability, growth kinetics, etc. The phenotypic results from the above experiments determined that the mutant showed variation in phenotypic characters from that of wild-type strain. Subsequently, mutant and wild-type NTS were subjected to epithelial cell invasion and intracellular replication assays. The real-time PCR analysis was also performed to analyse expression of tumor inhibiting cytokine genes and virulence genes post-bacterial infection in cell lines. The mutant showed highest invasion potential than wild-type NTS whereas the replication of mutant was slower in both the cell lines. Similar to the wild-type strain, the mutant also retained the cytotoxic potential when analysed in vitro. Furthermore, the expression of proinflammatory cytokine genes such as TNF-α and IL-1β was upsurged with the downregulation of anti-inflammatory cytokine genes like TGF-β, IL-6 and IL-10 post-infection of the mutant strain in cell lines. In addition, virulence genes of Salmonella pathogenicity island one and two of mutant were downregulated in vitro except invA in HeLa cell line. Therefore, the auxotrophic mutant showed positive attributes of a potential antitumor agent in terms of expressing tumor inhibiting cytokine genes when assessed in vitro. Though the study did not check the tumor inhibitory effect of NTS strain directly, findings of the study emphasizes on the development of a novel strain of NTS with less virulence and more immunogenic traits to inhibit tumor cells.

Antitumor effects and mechanisms of CpG ODN combined with attenuated Salmonella-delivered siRNAs against PD-1

Numerous studies have focused on the treatment of melanoma, but the current therapies for melanoma have limited therapeutic effects. To find a more effective therapy for melanoma, we combined artificially designed CpG ODN (cytosine-phosphate-guanine oligodeoxynucleotides) and siRNAs (small-interfering ribonucleic acids) targeting PD-1 (programmed cell death protein 1), which were delivered by attenuated Salmonella to treat melanoma in mice, and explored the underlying antitumor mechanisms. We found that mice receiving the combination therapy had the smallest tumor size and the longest survival time. The possible mechanisms underlying this phenomenon include pathways mediated by cyclin D1, p-STAT3 (phosphorylated signal transducers and activators of transcription protein 3), MMP2 (matrix metallopeptidase 2) and cleaved caspase 3, since after treatment, the expression of cyclin D1, p-STAT3, and MMP2 decreased but that of cleaved caspase 3 increased; additional mechanisms include increases in the recruitment of immune cells to tumor sites and in the number of immune cells in mouse spleens and the upregulation of TNF-α (tumor necrosis factor) and IL-6 (interleukin 6). We demonstrated that the combination therapy composed of CpG ODN and PD-1-siRNA delivered by attenuated Salmonella exhibited a strong ability to inhibit melanoma and improve the antitumor immune responses of tumor-bearing mice.