SspA is required for lethal Salmonella enterica serovar Typhimurium infections in calves but is not essential for diarrhea

Salmonella pathogenicity island 1 (SPI-1) encodes virulence determinants, w hich are important for enteropathogenicity in calves, To determine whether the Salmonella enterica serovar Typhimurium SPI-1 effector proteins SspA an d SptP are important far enteropathogenicity, strains lacking these protein s were tested during oral infection of calves. Calves infected with a sptP mutant or its isogenic parent developed diarrhea and lethal morbidity. In c ontrast, calves infected with an sspA mutant developed diarrhea, which reso lved within 10 days but did not result in mortality. The sspA mutant was re covered from bovine intestinal tissues at numbers similar to those obtained for its isogenic parent and caused marked intestinal lesions. Thus, the se verity of pathological changes caused by serovar Typhimurium strains or the ir ability to cause diarrhea were not predictive of their ability to cause lethal morbidity in calves. We conclude that factors other than or in addit ion to bacterial colonization, intestinal lesions, or electrolyte loss cont ribute to lethal morbidity in calves infected with serovar Typhimurium.