Examination of poultry litter for Salmonellae by direct culture and fluorescent antibody technique

Direct culture and fluorescent antibody (FA) procedures were used for examining approximately 6200 samples of poultry floor or nest litter for salmonellae. Each sample was cultured directly in tetrathionate brilliant-green (TBG) broth, incubated at 42 C for 48 hours, and plated on brilliant green (BG) agar. The FA procedure was conducted from pools of 4-8 samples prepared by transferring 1 ml supernatant from TBG at 24 hr into 50 ml of either gram-negative (GN) broth, selenite cystine, or selenite brilliant-green sulfapyridine. After 6 hr of incubation at 42 C, BG agar plates were streaked from each pool, and smears were prepared for FA. Salmonella was isolated by plating from 268 of 854 pooled units. Recovery was 97% by direct culture, 86% from GN broth, and 57% from the selenite secondary enrichments. In the FA procedure, GN broth was superior to either of the selenites as the secondary medium from which to prepare smears, giving more FA-positive pools, a higher percentage of confirmed positives, and a lower percentage of false negative pools. FA examination of litter samples can be expedited by using sample pools. A major deficiency of the FA technique was the high percentage of false-positive reactions as judged by inability to isolate salmonellae. From litter cultured directly in TBG, salmonellae were isolated from 97% of the total number of pools culturally positive by combined culture methods.