Differences between the global transcriptomes of Salmonella enterica serovars Dublin and Cerro infecting bovine epithelial cells

Authors: Salaheen, Serajus; Kim, Seonwoo; Van Kessel, Jo Ann; Haley, Bradd

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2022
Publication Date: 6/22/2022
Citation: Salaheen, S., Kim, S., Van Kessel, J.S., Haley, B.J. 2022. Differences between the global transcriptomes of Salmonella enterica serovars Dublin and Cerro infecting bovine epithelial cells. BMC Genomics. https://doi.org/10.1186/s12864-022-08725-z.
DOI: https://doi.org/10.1186/s12864-022-08725-z

Interpretive Summary: Salmonella enterica serovar Dublin (S. Dublin) is known to cause severe infections in humans and infections with this serovar have increased in recent years. S. Dublin is often associated with persistent infections in cattle and can lead to production losses and mortality. The emergence of S. Dublin as one of the most identified serovars in sick dairy cattle and calves is a major concern for the US dairy industry. S. Dublin is a genetically diverse serovar, but there is little information regarding the impact of isolate or strain diversity on colonization of the bovine gut. This study investigated host-pathogen interactions by co-culturing bovine epithelial cells and cells of different S. Dublin strains in vitro and characterizing the bacterial transcriptomes. Transcript profiles of two S. Dublin strains during interactions with bovine epithelial cells were described and results indicated that different, strain-dependent, gene expression profiles have a role during S. Dublin infection of bovine epithelial cells. Despite the potential for different mechanisms of host-pathogen interactions, the genetically-distant S. Dublin strains had similar infection and survival rates within the bovine epithelial cells. This study furthered our understanding of the potential genes that are important during infection and colonization of S. Dublin in cattle. Results from this study may be used to identify specific drug targets or management strategies that can be leveraged to reduce occurrences of S. Dublin in dairy animals.

Technical Abstract: Salmonella enterica serovar Dublin (S. Dublin) is a cattle-adapted serovar and is known to cause fatal infections in humans and dairy animals. S. Dublin is a genetically diverse serovar and there is little information regarding the impact of this diversity on colonization of the bovine gut. The aim of this study was to compare the host-pathogen interaction and associated global transcriptomes of genetically distant S. Dublin strains during infection of bovine epithelial cells. Two S. Dublin strains (A and B) that were recovered from bulk tank milk (raw milk at the farm) on two commercial dairy farms in the US and had a Dice similarity index of 80% were included in the study. When the strains were individually cultured with bovine epithelial cells, there were no significant differences observed between the strains in the number of associated (attached and invaded bacterial cells combined) or invaded/intracellularly survived cells. RNA-Seq analyses were conducted to compare the transcriptomes of the two S. Dublin strains during bovine epithelial cell infection. In total, 207 differentially-expressed genes (DEGs) were identified with at least 2-fold differences in the transcript abundances between the two strains (false discovery rate = 5%). Major differences were observed between the transcriptomes in some functional categories of DEGs, included cell motility (n=48), transcription regulators (n = 15), energy production and conversion (n=13), amino acid transport and metabolism (n = 13), and cell wall/envelop/membrane biogenesis (n=12). Based on enrichment analysis, pathways associated with bacterial motility and chemotaxis were over expressed in strain A compared with strain B. An in vitro motility assay confirmed that strain A was significantly more motile on semi-solid agar medium compared with strain B. Results from this study revealed that genetically distant S. Dublin bovine strains (with varied motility and diverse gene expression profiles) may infect and survive within bovine epithelial cells at similar rates, although results also suggest that the suite of molecular mechanisms influencing host-pathogen interactions may vary between S. Dublin populations.