While many of us are aware of the benefits of probiotics on gut health, we have also started using probiotics to ensure the safety of alternative formats of pet food. While not new in the vast amount of research in food safety, the addition of probiotics as a safety step is relatively innovative in the pet food space.

Primal Pet Foods has always adhered to a science-forward approach to ensure we continue to make raw food even safer for our consumers and their pets. As we continue to research and learn more about alternative pet food formats such as raw and freeze-dried, we’ve been able to deepen our understanding of the safety measures that are available.

The selected probiotic blend that Primal Pet Foods uses in its freeze-dried formulas are inhibitory due to multiple mechanisms. For example, the selected strains are known to compete with other types of bacteria for physical space, binding sites, and resources to survive. The process is known as competitive inhibition (1,2). This means that the probiotics we use will displace, outcompete, and inhibit any potentially harmful pathogens such as Salmonella spp., E. coli and Listeria monocytogenes, helping prevent/eliminate potentially harmful bacteria from our pet’s food. Another mechanism which offers lethality is using strains of probiotic bacteria that contain within them natural, antimicrobial compounds that can directly inhibit or kill pathogens. This ensures an additional benefit that the probiotics in our formulas will continue to fight harmful pathogenic bacteria long after the product leaves our warehouse.

Primal has always used a combination of preventive controls such as inbound raw material testing, a finished product “test and hold” protocol and high-pressure processing (HPP). Most recently, we started using probiotics as a safety step for our freeze-dried foods. After extensive research, both internally and externally at third-party facilities, we have been able to show that the addition of non-pathogenic bacterial cultures (probiotics) keeps our freeze-dried products free from harmful pathogenic bacteria for the pets who consume them as well as the humans who handle them (3).

We partnered with a third-party organization, which operates an ISO 17025 accredited laboratory and a pathogen research facility for food safety testing and research, to conduct a series of validation studies on using probiotics for safety in pet food. The studies, which began in late 2021, were designed to evaluate whether the proprietary probiotic blend we use in our freeze-dried products effectively eliminates harmful pathogenic bacteria such as Salmonella spp. or Listeria monocytogenes.

Primal provided the ingredients and formula details so the scientists could replicate batches of our freeze-dried formulas in their laboratory. Once the products were made, they were tested for background flora and frozen in sterile bags. Once the frozen product was properly thawed, the scientists inoculated them with a very high concentration of harmful pathogenic bacteria. In our most recent study, Listeria monocytogenes and Salmonella spp. were added in ranges 10^3 to 10^5 CFU/g. This step was conducted in a Biosafety Level 2 laboratory.

From there, the scientists separated the product into two batches – Batch 1 was treated with the probiotic blend while Batch 2 received no probiotics. Both batches of product were formed into our signature “nugget” shape and re-frozen. Each batch was analyzed for probiotic concentration and the amount of the target harmful pathogenic bacteria.

The scientists used our precise operating procedures (including time and temperature) for the drying step, replicating what is done in our own facilities. Each freeze-dryer tray had an equal amount of both batches. Immediately after drying, each batch was stored in sterile bags at ambient room temperature for over a month (~35 days). Throughout that timeframe, each batch was tested 10 different times for water activity, moisture percentage, concentration of the target bacteria and presence/absence of the target harmful pathogenic bacteria, and concentration of probiotics.

In conclusion, the third-party scientists confirmed that the addition of the probiotic blend to our freeze-dried product inhibited Listeria monocytogenes until it reached non-detectable levels by Day 3 and Salmonella spp. by Day 5. This inhibitory effect continued for the duration of the study. In the control group (that was not treated with probiotics), all pathogens remained at detectable levels throughout the trials. Additionally, similar results were found with in-plant verification studies utilizing the naturally occurring microflora.