Genome-Wide Screen of Salmonella Genes Expressed during Infection in Pigs, Using In Vivo Expression Technology

Pigs are a food-producing species that readily carrySalmonella but, in the great majority of cases, do not show clinical signs of disease. Little is known about the functions required bySalmonella to be maintained in pigs. We have devised a recombinase-based promoter-trapping strategy to identify genes with elevated expression during pig infection withSalmonella enterica serovar Typhimurium. A total of 55 clones with in vivo-induced promoters were selected from a genomic library of ∼10,000 randomSalmonella DNA fragments fused to the recombinasecre , and the cloned DNA fragments were analyzed by sequencing. Thirty-one genes encoding proteins involved in bacterial adhesion and colonization (includingbcfA, hscA, rffG , andyciR ), virulence (metL ), heat shock (hscA ), and a sensor of a two-component regulator (hydH ) were identified. Among the 55 clones, 19 were isolated from both the tonsils and the intestine, while 23 were identified only in the intestine and 13 only in tonsils. High temperature and increased osmolarity were identified as environmental signals that induced in vivo-expressed genes, suggesting possible signals for expression.