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Salmonella is one of the most important food safety and sanitation concerns worldwide, with the CDC estimating over one million illnesses reported each year. Poultry products are one of the main sources linked to Salmonella in the human food chain, in spite of the fact that the industry implements control strategies throughout production. When humans are infected, the short-term effect of Salmonella is foodborne illness, but the distrust in the food products that led to the illness can be felt long-term. For poultry producers, foodborne illness results in food waste, recalls, lost revenue and loss of brand reputation.
As poultry meat and eggs are two main agricultural goods traded globally, food inspection agencies are implementing stricter policies for Salmonella. The “zero Salmonella” claim is sought after but has caused debate around the world, with just a few programs able to manage a significant, continuous reduction of this organism in the food chain. Depending on the country, this means that samples are collected as early as the laying bird farms and as late as post-processing and analyzed for Salmonella on a yes (positive) or no (negative) basis. Having a negative result means that the level of Salmonella is not high enough on that sample to be detected at that time. The challenge with reaching “zero Salmonella” is that prevention and monitoring policies must be implemented throughout production, a tedious but necessary task.
Salmonella is regularly found in the poultry microbiome. There are over 2,500 variants (serotypes) associated with poultry, with very few causing illness in poultry and more causing illness in humans. When testing poultry flocks and food products for Salmonella, serotyping is important because it tells you if flocks contain Salmonella that can cause harm to humans.
Usually, Salmonella contamination starts with a bird consuming contaminated feed, debris or fecal material (Chadwick, 2017). Salmonella can colonize in multiple locations throughout the poultry gut and, if there is damage or stress to the gut, it can move into circulation and colonize in other internal organs (Martha Pulido-Landínez, 2019). It will compete with the native gut microbiota for colonization sites and food sources. Once colonized, it can replicate and move throughout the digestive tract, being found from crop to the ceca. The lining of the poultry gut is shed every few days, so Salmonella is shed in the feces to the rest of the flock. In laying hens raised in cages, there is concern with vertical transmission of Salmonella from the parent to the egg. In laying hens raised in cage-free/free-range systems as well as meat birds, vertical and horizontal transmission (between flock members) is of concern.
Ensuring all the Salmonella entry points throughout the production process--the feed and drinking water, breeding birds, the hatcheries, the broiler or laying hen farms and the processing facilities--are controlled, checked and regulated is necessary.
Feed comprises 70% of poultry production costs, thus efficient and sustainable utilization of feed ingredients and related resources is paramount to have the lowest possible feed cost with the least feed material waste. Salmonella contamination risk increases due to ingredients coming from multiple locations, and cross contamination in feed can derive from crop harvest, feed processing, transportation, and storage (Chadwick, 2017). Monitoring feed ingredients in the poultry diet that are Salmonella carriers, like protein and vegetable sources, can help reduce the risk of contamination. Feedmill equipment must also be regularly cleaned to reduce cross contamination (Martha Pulido-Landínez, 2019).
Feed hygiene in combination with water sanitation practices can help control which bacteria are consumed by the flock. One of the most effective feed hygiene strategies, addition of formaldehyde, can no longer be used in multiple countries due to regulatory restrictions. Chlorination and acidification treatments have been used in water to reduce bacterial populations. Organic acids are typically used for both feed as well as drinking water, which act by damaging the Salmonella bacterial cell wall due to their antimicrobial activity, reducing the amount of Salmonella in the feed that can colonize in the bird’s gut (Hajati, 2018).
The two contamination points in egg laying birds (laying hens and breeding hens)—the egg contents and the shell—can be controlled by reducing the amount of Salmonella in the hen’s gut.
Internal egg contents become contaminated when Salmonella bacteria from the digestive tract move into circulation through the damaged intestinal epithelium and then colonize in the reproductive tract. Once in the reproductive tract, Salmonella is transferred to the egg contents through the vitelline membrane (Gast et al, 2005). Salmonella is also shed in the hen’s feces, so contamination of the eggshell can occur if there is fecal material on the eggs. The porous structure of the eggshell allows for the movement of Salmonella from the feces into the egg. This is more likely to happen if the eggshell is of poor quality. Dirty layer eggs bring Salmonella risk to the egg processing facilities while dirty breeder eggs bring risk to the hatcheries.
Control points for Salmonella in both types of eggs can be regulated through managing the hen’s gut health and microbiome. If we can reduce gut colonization for internal egg contamination, and fecal shedding for external egg contamination, we can drastically reduce the likelihood of eggs carrying Salmonella.
Survey studies from China, Korea, Great Britain, and the Netherlands have shown that there can be a large variability in Salmonella detection at the hatchery, depending on sanitation practices (,Van Der Fels-Klerx et al., 2008, Ren et al, 2016, Ha et al., 2018, Oaster et al., 2022) . Even with strict sanitation processes in place, there is still a risk of contamination. Salmonella has been known to increase the ‘Exploders’ – the eggs exploding during the incubation and hatching processes due to overgrowth of pathogenic bacteria such as Salmonella- resulting in killing the embryo. Furthermore, dust, debris, and fecal material released from the Salmonella contaminated eggs during the incubation and hatching processes, lead to the spread of contaminates to other chicks in the same incubator or hatcher (Cason et al., 1994). Since chicks have an unestablished gut microbiota, Salmonella can easily travel to the gut for colonization sites and food with little competition.
With proper hatchery sanitation practices and the introduction of controlled competitive exclusion, we can reduce the risk of Salmonella in chicks before they go to the farm.
Broilers are most susceptible to Salmonella contamination and colonization in the first two weeks of life as their gut microbiota is naïve and in the process of getting established (Butcher and Miles, 2018). To outcompete Salmonella, the broiler gut needs consistent and continuous protection through grow-out with tools for competitive exclusion which can deprive Salmonella of places to colonize, as well as reducing the food sources available for Salmonella to colonize and proliferate. By protecting the health and integrity of the gut and improving nutrient utilization within the gut, less Salmonella can grow and replicate in that environment. This benefits the flock, with less spread of the pathogen between flock mates (horizontal transmission).
To control Salmonella in broiler and layers facilities, consistency is key. By reducing the Salmonella in the bird’s gut, you can help reduce the pathogenic loads entering the processing facilities.
With the processing facilities being one of the last stops before poultry products go to market, the importance of processors to utilize existing, new, and additional measures to prevent contamination. Contact, temperature, and time must be monitored to reduce bacterial growth and contamination. After slaughter, the poultry food product and equipment can be cleaned using various antimicrobials through either air or water chilling. Air chilling consists of hanging the carcasses individually and allow rapid air movement to reduce the temperature of the product. This process reduces the risk of cross contamination since each carcass is chilled individually. Water chilling consists of submerging the carcasses in a chilled water current with an antimicrobial for a set amount of time. The preventative measures in water chilling include: chlorine (less common now with current legislation) and organic acids. The methodology of chilling used is dependent on the regulatory agency and consumer preference.
Because of the potential for contamination all along the production process, achieving “zero Salmonella” requires a comprehensive strategy:
Products and services can be used independently, but to reach the goal of a “zero Salmonella” claim, we recommend following this multi-point risk management plan. We at DSM offer this comprehensive multi-point food safety solution, with the support of an end-to-end portfolio, that allows coverage throughout live production to reduce the opportunity for Salmonella to enter the food chain. This enhances the end product quality by reducing foodborne disease and food waste while maintaining consumer trust.
10 June 2022
Elle Chadwick is the Global Poultry Marketing Specialist at dsm-firmenich. She received her PhD in Poultry and Animal Science from North Carolina State University, USA. Elle has worked in the poultry and human health industries as a consultant for applied disease mitigation. She joined BIOMIN®, now part of dsm-firmenich, in 2021 as a Global Product Manager for Microbials.
Shelby Ramirez is the Global Poultry Technical Manager at dsm-firmenich Animal Nutrition & Health. She holds a PhD (Iowa State University) and MS (University of Illinois) in nutritional physiology and applied nutrition, respectively. She continued in research as a postdoctoral research at USDA and research manager at Biomin before her current role where she enjoys communicating science into application.
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