Effects of sample storage and delayed secondary enrichment on detection of Salmonella spp in swine feces
O'Carroll, J.M.; Davies, P.R.; Correa, M.T.; Slenning, B.D.
American Journal of Veterinary Research 60(3): 359-362
1999
ISSN/ISBN: 0002-9645 PMID: 10188820 Document Number: 510531
The effects of storage and delayed secondary enrichment (DSE) on detection of Salmonella spp. were investigated in faecal samples from 84 pigs in a commercial herd. Each faecal sample underwent 3 storage treatments: no storage (processed on the day of collection), storage at 4 degrees C for 6 days, and storage at -15 degrees C for 14 days. All stored samples were enriched in Rappaport-Vassiladias (RV) broth (single enrichment) and plated on XLT4 agar. Delayed secondary enrichment was performed, using single enrichment broths that were stored for 4 days at room temperature. Of 504 cultures, 186 (36.9%) were Salmonella positive. There was no difference in proportions of samples with positive results between same-day processing and storage at 4 degrees C for 6 days. Compared with single enrichment for 24 h (34% positive), use of DSE resulted in a greater proportion (40%; P<0.001) of samples with positive results. Estimated relative sensitivities for the storage methods were 0.90, 0.85, and 0.71 for same-day processing, storage at 4 degrees C for 6 days, and storage at -15 degrees C for 14 days, respectively. Where practical, processing of faecal samples on the day of collection is recommended, although storage at 4 degrees C for several days does not result in marked loss of sensitivity. Improved detection associated with DSE warrants further investigation and optimization.