Optimizing Salmonella Recovery From Commercial Poultry Environmental Samples With Selective Preenrichment

The current culture-based methods for detecting Salmonella are time and resource-intensive, as it can take between three to five days with preenrichment and selective enrichment steps. Previous work by our group has shortened this process by combining novobiocin and selective ingredients from Rappaport-Vassiliadis (RV) (malachite green; 0.1 g/L) and tetrathionate (TT) (bile salts; 1 g/L) to BPW in parallel, creating an all-encompassing selective preenrichment step. In this study, we sought to validate the use of selective preenrichment on commercial poultry live production samples, as the increased presence of background bacteria may limit Salmonella recovery. Two pairs of boot sock samples were collected from 35 houses, representing 17 different commercial broiler or breeder farms (n = 70 samples). The samples were cultured under selective preenrichment conditions in parallel with standard nonselective preenrichment (BPW), followed by selective enrichment (RV, TT). Additionally, molecular enumeration was performed to quantify the amount of Salmonella present in each sample. Overall, Salmonella was found in 74% (52/70) of samples collected, and selective preenrichment and selective enrichment conditions each recovered Salmonella in 14/17 farms. The average quantity per sample was greater in those recovered with selective preenrichment (5.2 log₁₀ CFU/sample) than those that were not (3.0 log₁₀ CFU/sample; p = 0.01, Welch two-sample t-test). CRISPR-SeroSeq was used to determine the relative frequency of Salmonella serovars in each sample and culture condition. The proportion of multiserovar populations observed in the selective preenrichment conditions (53%, 29/55) was not significantly different from those in selective enrichment conditions (56%, 39/70; p = 0.1, McNemar's chi-squared test). These findings suggest that increasing the selectivity of the Salmonella preenrichment step could eliminate the need for a subsequent selective enrichment, thus reducing the time to Salmonella isolation by 24 h.