Purpose: Develop and evaluate molecular and cultural methods to differentiate Salmonella Dublin in various bovine samples.
Methods: Salmonella Dublin strains (n = 25) and non-Dublin strains (n = 5) were inoculated (100 CFU/g) into bovine samples (colostrum, blood, feces) and their growth was evaluated in five selective enrichments [(Rappaport-Vassiliadis (RV; 2 formulations), tetrathionate broth (TT; 2 formulations), selenite cysteine broth (SC)] by a real-time PCR targeting invA and vagC genes. Differentiation between Dublin and non-Dublin strains was evaluated using Xylose Lysine Desoxycholate agar with arabinose (XLD+A), Modified Semisolid RV (MSRV), Simmon’s Citrate Agar (SCA), Congo Red Agar (CRA). All media were incubated at 37°C for 24 h prior to evaluation with the exception of CRA (25°C, 7 days).
Results: The highest cell densities (as determined by Ct values from PCR assay) and easiest isolation of Salmonella Dublin were achieved with TT (USDA formulation) and SC enrichments. Dublin strains displayed significantly different phenotypes than non-Dublin strains on MSRV and SCA; however, this was mostly due to Dublin’s inability to grow or demonstrate motility. Extended incubation on CRA produced the most distinct differentiation between the Dublin (smooth/white) and non-Dublin isolates (rough/red).
Significance: A simplified cultural method coupled with molecular screening was deemed suitable for isolating and differentiating Salmonella Dublin from background Salmonella spp. This method can be used to analyze a wide range of microbiologically complex bovine samples for shedding status and herd health decisions.