Comparative proteome and transcriptome analyses of wild-type and live vaccine strains of Salmonella enterica serovar Gallinarum.

Salmonella enterica serovar Gallinarum causes fowl typhoid in chickens and is of economic importance to the chicken industry. A serovar Gallinarum live vaccine strain 9R (SG 9R) has been used to control fowl typhoid in many areas where the disease is endemic. Because the attenuation mechanism of SG 9R was not defined, there has been continued concern about reversion to virulence. In this study, we examined the molecular characteristics, which might provide better insight into attenuation of SG 9R, by comparing its proteome and transcriptome with those of two wild-type strains (287/91 and 06Q110). Proteins present in wild-type strains but absent in SG 9R were identified by two-dimensional gel electrophoresis and MALDI-TOF MS. Genes up- or down-regulated in SG 9R compared to wild-type strains were identified using an expression array. The proteome analysis identified nine proteins absent in SG 9R of which one protein had relevance to virulence. The transcriptome analysis revealed 24 up-regulated and 97 down-regulated genes in SG 9R. Approximately one-half of down-regulated genes (42 genes) were associated with virulence mechanisms. This finding suggests that attenuation of SG 9R may be associated with a combination of impaired virulence factors and thus reversion to virulence would not be caused by any single mutation event.