Enrichment Serology Compared with a Direct-Culture Procedure for Isolating Salmonellae from Rendered Animal By-Products

Abstract

A direct-culture method and an enrichment serology (ES) procedure were compared for isolating salmonella from rendered animal by-products. SBG sulfa enrichment incubated at 42 C was used for direct culture of all 399 samples. Tetrathionate brilliant green (TBG) and SBG sulfa were used in the ES procedure with all samples, and selenite cystine (SC) with 144 of the samples; cultures were incubated at both 42 and 37 C for comparative purposes. All selective enrichment broth cultures in the ES procedure were plated to determine whether salmonellae were present in the medium used to seed the M-broth. Salmonellae were recovered from 182 samples; 76% were detected by direct culture and 86% by the pre-enrichment procedure. More cultures yielded salmonellae from both TBG and SBG sulfa incubated at 42 C than at 37 C; essentially no difference was noted for SC. In the ES procedure, TBG was superior to either of the selenite broths at both incubation temperatures, in that TBG yielded the highest percentage of agreement between cultural isolations and M-broth agglutination. Results indicated that cultural isolation is a more accurate method of detecting salmonellae from rendered byproducts than is agglutination from M-broth.