Submitted to: Poultry International Exposition
Publication Type: Abstract Only
Publication Acceptance Date: 12/19/2012
Publication Date: 1/29/2013
Citation: Cox Jr, N.A., Buhr, R.J., Cason Jr, J.A., Cray, P.J. 2013. Inherent weaknesses in the cultural methods used for Salmonella detection [abstract]. Poultry International Exposition. p. 25.
Technical Abstract: Expert consensus on the most appropriate sampling sites and methods for determining the Salmonella status of raw poultry and poultry products has never been reached. In addition, the lack of uniformity and inherent weaknesses in many frequently used methods complicates routine Salmonella detection. In poultry, the method of sampling a broiler carcass, the type of laboratory media used, and the number of colonies selected are only several factors that can influence the number of positive samples and/or serotypes isolated. Often two or more selective broths and plates are used to reduce the likelihood of false-negative results. In a recent study, postchill commercial broiler carcasses (neck skin, carcass rinse, or whole carcass enrichment) were sampled using multiple culture media [(tetrathionate and GN Hajna broths and Brilliant Green with Sulfadiazine (BGS) and XLT-4 agar plates)]. Only a single Salmonella serotype was detected using the rinse method while two and 5 different serovars using neck skin and carcass enrichment, respectively. Using the same media/agar combinations, from 49 naturally contaminated broiler carcasses BGS and XLT-4 yielded the same Salmonella serotypes 22% of the time whereas different serotypes were found for 78% of the samples. In another study 34 of 35 S. Lille isolates were recovered from BGS plates and not at all on XLT-4. Conversely, S. Kiambu isolates were detected exclusively on XLT-4 plates. These studies highlight the variability of detecting individual serotypes even when using only two plating media. In addition to culture media, the number of colonies selected and tested from a sample can dramatically influence the number of positive samples and the number and different serotypes encountered. When only one colony was selected from each plate, 42/52 broiler carcasses were Salmonella positive. If 2 or 3 colonies were tested from each plate, 49/52 were positive. By picking more than one colony an additional serotype was found on 40 of the 49 positive carcasses and on 23 of these 40, two or more additional serotypes were detected. More research is needed to better understand the limitations that exist in our laboratory methods for isolating Salmonella, particularly from raw poultry and poultry-related samples.