Serum Bactericidal Assay: New Role in Salmonella Detection

Abstract

While inspecting animal feed for Salmonella contamination, we routinely observed bacterial colonies on selective agars that were similar in appearance to those formed by Salmonella. These were identified as Citrobacter freundii, Proteus mirabilis, and Serratia fonticola using biochemical and serological techniques. Because the presence of these bacterial species confounds identification of Salmonella, we refer to them as "interference bacteria." Polyvalent antisera against these interference bacteria were prepared by immunizing rabbits with a mixture of all three organisms. To minimize or eliminate interference by these bacteria, the polyvalent antisera were introduced between the steps of selective enrichment and Salmonella-selective plating. The antisera raised against the interference bacteria, when combined with neonatal rabbit complement, exhibited specific bactericidal activity against C. freundii, P. mirabilis, and S. fonticola. The respective serum bactericidal assay titers were 2(9), 2(8), and 2(10). In selective broth, polyvalent antisera could also kill the target bacterial cells effectively. We tested 526 samples (186 white fishmeal, 97 red fishmeal, and 243 cattle bone powder) using the polyvalent antisera and found that the rates of contamination of each species of the three respective foods decreased by 58.8, 100, and 83%. Our data indicates that polyvalent sera against C. freundii, P. mirabilis, and S. fonticola can be used as inhibitors to increase the accuracy of Salmonella detection.

Establishment of a duplex real-time qPCR method for detection of Salmonella spp. and Serratia fonticola in fishmeal

“…in daily quarantine work. Furthermore, suspected Salmonella colonies based on selective plate isolation and culturing of imported animal-derived feeds often turn out to be S. fonticola when biochemical properties are investigated (Chen et al 2016). The enzyme linked immune sorbent assay (ELISA) method is commonly used for detecting pathogens in imported animal-derived feeds, but this method can produce incorrect results due to its cumbersome operational steps.…”

Establishment and Application of a duplex real-time qPCR method for detection ofSalmonellaspp. andSerratia fonticolain imported feedstuffs

“…in daily quarantine work. Furthermore, suspected Salmonella colonies based on selective plate isolation and culturing of imported animal-derived feeds often turn out to be S. fonticola when biochemical properties are investigated (11). The enzyme linked immune sorbent assay (ELISA) method is commonly used for detecting pathogens in imported animal-derived feeds, but this method can produce incorrect results due to its cumbersome operational steps.…”