Considering the high number of putative pathogenicity genes on SPI-23 and the higher number of isolations of S. Derby from pigs in the UK it was posited that this island may play a role in pathogenicity in this host. In the current study we undertake preliminary studies to start addressing this hypothesis; we show that S. Derby associates to, and invades, a porcine derived monolayer faster than S. Mbandaka and that SPI-23 is regulated in a tissue specific fashion. Furthermore a knock-out mutant of the most up-regulated gene, potR, results in cellular agglutination in a static culture. We discuss the possible role that potR and other SPI23 genes may play in tissue tropism. Though other studies have found poor concordance between monolayer WT161 invasion rates, pathogenicity and host association, the use of monolayers here shows that S. Derby is more proficient at associating and invading IPEC-J2 monolayers than S. Mbandaka. It was previously shown, with two strains of S. Typhimurium, that differences in invasion rates observed in IPEC-J2 SCH 619734 assays were comparable to those found in porcine mucosal explants. Though we may not assert that the more proficient association and invasion by S. Derby is the determinant of the bias towards a porcine host, we can suggest that S. Derby possesses adaptations for aspects of pathogenesis of the porcine host, that are absent in the comparator serovar, S. Mbandaka. Of course, it would be interesting to undertake a broader study of populations of a variety of serovars, especially the promiscuous serotypes such as S. Typhimurium, to assess whether this finding holds true across different serovars. The colon is also a site commonly associated with Salmonella invasion. To assess if there was preferential attachment by S. Derby to either of these tissues, porcine IVOC association assays were performed. Both S. Derby strains associated in significantly greater numbers with jejunum when compared to colon. After 30 minutes there were 2.5 times as many S. Derby D1 cells associated with the jejunum than the colon.