Comparison of sampling methods for the detection of Salmonella on whole broiler carcasses purchased from retail outlets

An experiment was conducted to compare the effectiveness levels of two methods in recovering Salmonella from the same carcass. One hundred fresh whole broiler chickens were purchased from retail outlets over a 5-week period (20 carcasses per week). After carcasses had been aseptically removed from the packages and giblets had been removed, the carcasses were placed in sterile bags containing 400 ml of 1% buffered peptone water, the bags were shaken for 60 s, and a 30-ml aliquot was removed and incubated for 24 h at 37°C (aliquot sample). Then, an additional 130 ml of 1% buffered peptone water was immediately added to the bag with the carcass (bringing the volume to 500 ml), the bag was reshaken, and the carcass and rinse were incubated for 24 h at 37°C (whole-carcass enrichment sample). Following incubation, 0.5-ml samples for the two methods were placed into 10 ml of Rappaport-Vassiliadis broth and into 10 ml of tetrathionate (Hajna) broth and incubated at 42°C for 24 h. Each broth was then streaked onto BG Sulfa agar and modified lysine iron agar and incubated for 24 h at 35°C. Suspected Salmonella colonies were inoculated onto triple sugar iron and lysine iron agar slants and incubated at 35°C for 24 h. Presumptive positive results were confirmed by Poly O and Poly H agglutination tests. Over the 5-week period, 13% of the aliquot samples tested positive for Salmonella, compared with 38% of the whole-carcass enrichment samples from the same carcasses. Recovery rates ranged from 0 of 20 samples to 4 of 20 samples for aliquot method and from 4 of 20 samples to 10 of 20 samples for the whole-carcass enrichment method over the 5-week period. These results indicate that when small numbers of Salmonella are expected, the sampling method has a major influence on the identification of Salmonella-positive carcasses.