Abstract
Salmonella enterica serovars Derby and Mbandaka are isolated from different groups of livestock species in the UK. S. Derby is predominantly isolated from pigs and turkeys and S. Mbandaka is predominantly isolated from cattle and chickens. Alignment of the genome sequences of two isolates of each serovar led to the discovery of a new putative Salmonella pathogenicity island, SPI-23, in the chromosome sequence of S. Derby isolates. SPI-23 is 37 kb in length and contains 42 ORFs, ten of which are putative type III effector proteins. In this study we use porcine jejunum derived cell line IPEC-J2 and in vitro organ culture of porcine jejunum and colon, to characterise the association and invasion rates of S. Derby and S. Mbandaka, and tissue tropism of S. Derby respectively. We show that S. Derby invades and associates to an IPEC-J2 monolayer in significantly greater numbers than S. Mbandaka, and that S. Derby preferentially attaches to porcine jejunum over colon explants. We also show that nine genes across SPI-23 are up-regulated to a greater degree in the jejunum compared to the colon explants. Furthermore, we constructed a mutant of the highly up-regulated, pilV-like gene, potR, and find that it produces an excess of surface pili compared to the parent strain which form a strong agglutinating phenotype interfering with association and invasion of IPEC-J2 monolayers. We suggest that potR may play a role in tissue tropism.
Highlights
Salmonella enterica is an important zoonotic pathogen of warm blooded vertebrates, including humans and livestock
IPEC-J2 monolayers have been used previously as a model for the porcine jejunum, a site associated with the invasion of Salmonella enterica [12,13,14]
Derby to porcine jejunum compared to colon and the need to characterise the newly discovered Salmonella pathogenicity island (SPI)-23 in relation to pathogenesis in the porcine host, we investigated if there was a difference in transcriptional regulation of the island when the serovar was exposed to the different tissue types
Summary
Salmonella enterica is an important zoonotic pathogen of warm blooded vertebrates, including humans and livestock. International serotyping has provided statistics that have elucidated links between certain serovars and a defined host species range [4,5,6,7]. In previous work the chromosome sequences of S. enterica serovars, Derby and Mbandaka were compared [8]. Isolation statistics suggest that these serovars have different host species biases in the UK: S. Alignment of the chromosome sequences led to the discovery of a new putative Salmonella pathogenicity island (SPI) in isolates of S. SPI-23 is 37 kb in length and encodes 42 genes, ten of which were identified by the online tool SEIVE as putative type 3 effector proteins; of these eight were unique in nucleotide sequence to S. Type III effector proteins are important pathogenicity factors secreted through the type III secretion system in to a host cell where they modulate cell signalling, in some instances pacifying the hosts immune system or aiding in invasion of, or translocation across, the intestinal epithelial barrier [10,11]
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