Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2007
Publication Date: 1/5/2008
Citation: Harhay, D.M., Arthur, T.M., Koohmaraie, M. 2008. Enumeration of Salmonella from poultry carcass rinses via direct plating methods. Letters in Applied Microbiology 46(2):186-191. Interpretive Summary: Assuring the microbiological safety of poultry is of great importance to consumers and to the poultry industry. Prevalence of foodborne pathogens is routinely monitored by industry and researchers. However, accurate, economical and high-throughput methods for testing the levels of pathogens such as Salmonella, at various steps in the poultry production process have not been available. It would greatly increase the processing industry’s ability to ensure safe product if they could routinely determine not only whether pathogens are present, but if so, at what level. Thus, we evaluated two direct plating methods for the enumeration of Salmonella from poultry carcass rinse samples. The direct plating methods described can be performed in a fraction of the time and at a fraction of the cost of the traditional most probable number enumeration method. Use of the direct plating methods will facilitate increased monitoring of the levels of Salmonella on poultry carcasses throughout the production process, allowing for the evaluation of new and improved intervention strategies, and improving poultry carcass hygiene.
Technical Abstract: Direct plating methods for the estimation of Salmonella load in poultry carcass rinses were evaluated. Twenty broiler carcasses were collected weekly for three weeks from each of three sites (pre-inside outside bird wash [Pre-IOBW], Pre-chill and Post-chill) in a poultry abattoir resulting in 60 carcasses evaluated from each site, and a total of 180 carcasses examined. The direct plating methods evaluated were the spiral plate count method (SPCM) and hydrophobic grid membrane filtration (HGMF). The mean percent prevalence of Salmonella in carcass rinses was found to be 95 % for Pre-IOBW, 100 % for Pre-chill and 42 % for Post-chill samples. The SPCM was used to evaluate Pre-IOBW carcass rinse samples, and 51% (29/57) had Salmonella above the operational limit of detection of 5 CFU per mL. The overall geometric mean of Salmonella load in these Pre-IOBW samples was 1,050 CFU/100 square cm with a 95% confidence interval (CI) of 199 to 5,480 CFU/100 square cm. The HGMF method was used to enumerate Salmonella in Pre-chill and Post-chill carcass rinse samples and 53 % (32/60) and 68 % (17/25) of the samples had Salmonella above the detection limits of 1.0 and 0.025 CFU per mL, respectively. The overall observed geometric means of Salmonella load present in these samples were 195 CFU/100 square cm with a 95% CI of 50.2 to 762 CFU/100 square cm for Pre-chill carcass rinses and 0.75 CFU/100 cm2 with a 95% CI of 0.52 to 1.08 CFU/100 square cm for Post-chill samples. Traditionally, the gold standard for enumeration methods is the most probable number (MPN) method. A comparison of the HGMF and SPCM to MPN showed that the alternative methods gave comparable results, with the benefits of increased sample throughput and decreased labor and cost.