Salmonella enterica is linked to a number of human illnesses every year, with a proportion of cases linked to poultry consumption. Considering the public health risk Salmonella poses, the U.S. Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) recently began to reevaluate its approach to Salmonella.
In 2021, FSIS unveiled their Salmonella Roadmap, followed by the release of the “Proposed Regulatory Framework to Reduce Salmonella Illnesses Attributed to Poultry” in December 2022. The policy framework aims at improving regulatory standards concerning pre-harvest flock testing, process control points, and final product standards based on quantification.
Background
With the emergence of newly proposed regulations that have tighter focus on pre-harvest Salmonella control, an emphasis has been placed on methodologies to measure and thus help mitigate Salmonella. Conventionally, ceca samples have been used for evaluating and measuring the efficacy of pre-harvest interventions against foodborne pathogens in the live production environment. More recently, ceca samples have been used to assess incoming Salmonella load and to determine flock level Salmonella risk to the harvest facility.
As such, ceca are currently considered a “gold-standard” sample for Salmonella detection within the poultry industry. In many experiments, ceca often has presented as an organ with the highest levels of Salmonella contamination when compared to other organs. Additionally, cecal infection has served in experiments as a baseline for the extent of which Salmonella contamination has occurred.
However, conflicting research also has shown alternative organs may be more sensitive than ceca, such as trachea, lung, liver and spleen, especially when samples are collected at the harvest facility after feed withdrawal. With conflicting evidence regarding Salmonella detection in ceca and current efforts to mitigate Salmonella contamination, the effectiveness of ceca as an indicator of poultry contamination needs further evaluation.
The team of Dr. Anna Carlson from Cargill and Dr. Nikki Shariat from the University of Georgia recently completed a project funded by USPOULTRY to assess the use of high-resolution Salmonella serotyping to improve surveillance in turkey production. While the use of ceca as a predictive sample was not the intention of the project, their data demonstrated a clear lack of relationship between ceca Salmonella and Salmonella in both ground turkey and mechanically separated turkey.
A second study, funded by the National Institute of Food and Agriculture and being completed by Dr. Anna Carlson and Dr. Jessie Vipham from Kansas State University, also has demonstrated similar trends.
An overview of the findings can be found below.
Methods and Results
Study 1 (US POULTRY)
In this study, 22 flocks were sampled at different stages of processing, including six composite samples (consisting of 10 ceca per composite), six ground turkey samples and six mechanically separated turkey samples from each flock. Fewer than one in 10 (12/132) ceca samples were Salmonella-positive by traditional culture methods, while more than a quarter of grind (35/132) and mechanically separated turkey (39/132) samples were positive.
Moreover, five flocks had Salmonella-positive ceca, while Salmonella was isolated from ground turkey and mechanically separated turkey in 13 and 10 flocks, respectively. In all but one flock, a single serotype was found in ceca samples, while multiple serotypes were detected in ground turkey and mechanically separated turkey.
Study 2 (Kansas State)
In this study, 36 flocks were chosen to evaluate the effectiveness of ceca as a predictive sample of Salmonella in ground turkey through an analysis of ceca samples (360 total) and ground turkey samples (72 total). Of the total ceca samples, only 3.88% (7/360) were positive for Salmonella and 1.38% (5/360) were quantifiable. Conversely, of the total ground turkey, 30.55% (22/72) were positive and 20.83% (15/72) were quantifiable.
On a flock level, Salmonella incidence was higher in ground turkey samples when compared to ceca samples. Overall, eight of the total 36 flocks evaluated (22%) produced a positive result for Salmonella from ceca samples, while 13 of the total 36 flocks (36%) produced positive ground turkey results. Interestingly, only two flocks were found to be positive for both ceca and ground turkey samples.
When reviewing Salmonella quantification data across flocks, ceca Salmonella levels ranged between 0.45 to 1.34 Log CFU/mL, while ground turkey samples ranged from-1.4 log CFU/g to 2.54 Log CFU/g.
Conclusions
Currently, there is a fundamental lack of data regarding pre-harvest Salmonella testing methods and quantification limits for predicting ground turkey test results. Additionally, the turkey industry does not have an established metric for predicting final product test results (e.g., Salmonella limit of detection testing).
In comparison, the ground beef industry has used N60 testing for Escherichia coli O157:H7 since the early 2000s. Although this exact method is not appropriate for ground poultry products, the premise of using a testing methodology to divert product prior to grind holds significant promise in reducing Salmonella in ground poultry products.
While ceca samples have been considered a “gold-standard” sample for Salmonella detection within the poultry industry for many years, this research indicates that ceca sampling during turkey processing is not an adequate predictive sample for ground turkey Salmonella test results.
Ceca and ground turkey samples presented different frequencies of Salmonella detection and quantification values, and some serotypes found in ground turkey and mechanically separated turkey were not found in the ceca. Overall, ceca samples resulted in very low rates of Salmonella detection.
The contrasting results (through prevalence, quantification and serotyping) between ceca and ground turkey samples clearly indicate that ceca samples are likely to underperform in predicting the Salmonella rates in final ground samples.
Dr. Denise Heard is vice president, research programs at the U.S. Poultry and Egg Association; Dr. Anna Carlson is senior research scientist at Cargill; and Dr. Nikki Shariat is assistant professor of veterinary medicine at the University of Georgia.
