The shdA gene is restricted to serotypes of Salmonella enterica subspeciesI and contributes to efficient and prolonged fecal shedding

Little is known about factors which enable Salmonella serotypes to circulat e within populations of livestock and domestic fowl. We have identified a D NA region which is present in Salmonella serotypes commonly isolated from l ivestock and domestic fowl (S. enterica subspecies I) but absent from repti le-associated Salmonella serotypes (S. bongori and S. enterica subspecies I I to VII). This DNA region was cloned from Salmonella serotype Typhimurium and sequence analysis revealed the presence of a 6,105-bp open reading fram e, designated shdA, whose product's deduced amino acid sequence displayed h omology to that of AIDA-I from diarrheagenic Escherichia coli, MisL of sero type Typhimurium, and IcsA of Shigella flexneri. The shdA gene was located adjacent to xseA at 52 min, in a 30-kb DNA region which is not present in E scherichia coli K-12. A serotype Typhimurium shdA mutant was shed with the feces in reduced numbers and for a shorter period of time compared to its i sogenic parent. A possible role for the shdA gene during the expansion in h ost range of S. enterica subspecies I to include warm-blooded vertebrates i s discussed.