Verification of different methods used for isolating Salmonella enterica serovar Dublin from cattle feces.

Salmonella enterica serovar Dublin is a cattle-adapted serovar, and some infected cattle can become asymptomatic carriers. Identification of carrier animals is important for preventing the spread of infection within a farm, but low diagnostic sensitivity of the fecal culture method is problematic. In this study, we investigated isolation methods of four S. enterica Dublin strains. Selective enrichment using the tetrathionate broth showed better performance than Rappaport-Vassiliadis R10 broth, but one of the strains was not detectable. Since isolation of such strains by selective enrichment can be difficult, we designed a method using immuno-plates that concentrates S. enterica Dublin by antigen-antibody reaction. Our method is able to detect approximately 200 clony-forming units of S. enterica Dublin in 0.1 g of cattle feces. If S. enterica Dublin was isolated from cattle with clinical signs, the method to identify carriers in the farm should be based on the growth kinetics of the target S. enterica Dublin strain.