Fluorescent-Antibody Methods for Detecting Salmonellae in Animal By-Products

SUMMARY Direct-culture and fluorescent-antibody (FA) procedures were used for examining 550 samples of rendered animal by-products for salmonellae. Tetrathionate brilliant-green (TBG) and selenite bril­ liant-green sulfapyridine (SBG sulfa) enrichments incubated at 42 C respectively detected 82% and 73% of the 158 samples found positive by these two direct-culture methods. Three FA procedures were tested in parallel. TBG, SBG sulfa, and gram-negative (GN) broth, the last recommended by the USDA, were used for primary enrichment followed by subculturing for 5-6 hr in GN broth from which FA smears were prepared and brilliant­ green agar plates were streaked. There were 454 subcultures which were FA-positive from the three procedures used, and salmonellae were recovered from 342. Of the 150 subcultures which were FA-questionable, salmonellae were recovered from 14; and of 1,046 subcultures which were FA­ negative, the organism was isolated from 17. The data indicated that SBG sulfa and TBG can be substituted successfully for GN broth as the FA primary enrichment. This sub­ stitution resulted in greater correlation between FA results and salmonella isolations.