Ever hear what they say about ducks?
“Calm and unruffled on the surface but paddling like heck underneath.”
The same could be said for pathogen measurements in meat and poultry plants. Essentially, all processing facilities already measure prevalence—or presence—of bacterial pathogens such as Salmonella. Measuring pathogen load can also help plant managers dive more deeply under the surface and, ultimately, uncover ways to improve food safety management.
Understanding Pathogen Prevalence
The USDA Food Safety and Inspection Service (FSIS) uses pathogen prevalence, as indicated by performance standards as the primary process control measure to evaluate the safety of meat and poultry products.
Prevalence is a yes or no answer—it’s either yes, the pathogen is present, or no, it’s not. Prevalence is expressed as a percentage of samples tested. For example, if you’re testing 100 poultry carcasses, and 20 test positive for Salmonella, the prevalence is 20%.
Salmonella prevalence indicates pathogen presence, but it does not indicate whether the positive result is due to one cell or many cells. To determine prevalence, the collected sample goes through an enrichment process that provides nutrients and temperature conditions favorable to the growth of Salmonella. This enrichment step allows the number of Salmonella cells to replicate over time and reach a level that allows presence to be detected. This methodology produces a positive prevalence result, even if the Salmonella cell numbers are low in the initial sample.
To protect public health, FSIS looks for processing plants to reduce pathogen prevalence at every step, from animals or birds coming into the plant all the way to the outgoing final product.
Plant managers often use prevalence testing to assist with process control. A poultry processor might take samples from five or more areas, such as rehang, post-pick, pre-chill, post-chill, and final product. Prevalence testing will confirm the desired decrease in pathogen presence at every step. If prevalence increases, that may signal a problem requiring an additional intervention at that step, or it may indicate a needed improvement in the management of a system or process.
What Is Pathogen Load?
Recently, more companies have started measuring pathogen load in addition to pathogen prevalence. Also referred to as enumeration, load data supplements the prevalence yes-or-no answer by measuring the number of cells of a particular pathogen present in a sample. With new technology, load testing can detect very low numbers of pathogen cells.
Since bacterial cells grow logarithmically, load is expressed via a log10 scale versus a numerical scale. For instance, 101 log CFU/g equals 10 cells, 102 log CFU/g equals 100 cells, 103 log CFU/g equals 1,000 cells, and so on.
Why Pathogen Load Matters
Pathogen load measurements tell the plant manager the number of actual bacteria in the system, not just their presence. The higher the pathogen load, the higher the potential food safety risk, especially at the final product. By measuring both prevalence and load, plant managers can get a robust and real-time picture of what’s happening in the plant.
It’s possible to have high pathogen presence and low pathogen load, if many of the carcasses test positive but each one carries only a few cells. If only a few carcasses carry high levels of contamination, a plant might have low pathogen presence and high pathogen load. Each of these scenarios may require further investigation to determine if the process is under control and to identify solutions to reducing prevalence and/or load to ensure final product food safety.
Load measurements can provide additional data to help managers determine both what’s working well and where improvements may be needed. Understanding load can identify areas to apply antimicrobials, areas where process control may be failing, or areas where equipment or system management could be improved. This concept is especially true when validating an antimicrobial. Reducing load is the goal of an antimicrobial, and this can be easily measured with pre- and post-intervention sample testing. This method of validating an antimicrobial also takes into consideration variation that exists in processing.
Using Pathogen Load Data
Finding sources of cross-contamination is one way for managers to use enumeration or load data. Cross-contamination can be an issue in meat and poultry production: One animal or group of animals can contaminate others, and improperly adjusted equipment can potentially create a cross-contamination issue.