Diverse pathogenicity of Salmonella enteritidis clones isolated from poultry farms in chicks and BALB/c mice

Oral infection of Salmonella enterica serovar Enteritidis (SE) strains, SE No.15, SE No.26, and SE No.56, isolated from poultry farms was performed with specific pathogen-free (SPF) 1-day-old chicks and 6 weeks-old BALB/c mice. SE No.15 showed the strongest lethality to both chicks and mice, and SE No.26 or No.56 showed no effects on the survival of mice, while SE No.26 showed little and SE No.56 intermediate lethal effects to chicks. Using reverse transcriptation-PCR (RT-PCR), expression of pathogenic genes in these SE clones was examined; flagella (fliC), invading host cell (invA), Salmonella enterotoxin (stn) and DNA-binding protein from starved cells of Salmonella (sep22) genes were expressed in SE No.15 and SE No.56, whereas invA was negative in SE No.26. However sep22 was more weakly expressed in SE No.26 and SE No.56 than SE No.15. Western blot analysis of total protein extracts of these SE strains revealed that SE No.15 expressed highest levels of SEp22, while SE No.26 and SE No.56, significantly lower levels of this protein than SE No.15. This study showed the extents of sep22 expression at mRNA as well as protein level correlated well with pathogenicity of SE clones to chicks and mice, and these results suggest that SEp22 is a new virulence factor in both chick and mouse.