Probiotic Application Reduces Salmonella Enteritidis Contamination in Layer Hatching Eggs and Embryos

Project Director: Mary Anne Amalaradjou, University of Connecticut

Project Overview

Salmonella Enteritidis (SE) is a common type of bacteria that can cause food poisoning and intestinal illness if consumed by humans. Raw poultry meat and eggs are a primary source of SE. The pathogen can spread rapidly through poultry flocks, transmitted by (1) consuming contaminated fecal matter; (2) coming into direct contact with other infected birds or equipment; (3) inhaling dried fecal matter; or (4) direct-transmission from an infected mother hen to her eggs. In this final mode of transmission, the pathogen can infect a developing yolk before an egg is even laid, or can migrate from the eggshell surface into the developing embryo shortly after oviposition. Infected hatchlings can spread SE both within their original flock or across flocks, if sold to other farms.

Conventional hatcheries employ a number of biosecurity protocols to prevent the transmission of diseases like SE; however, some of these practices, including formaldehyde fumigation (the release of formaldehyde gas in an enclosed space to kill surface bacteria and viruses) can negatively affect hatchling health and survival. New disease management practices with fewer health consequences for hatchlings are needed, including practices suitable for certified-organic hatcheries.

In this study, researchers in Connecticut evaluated several organic-compliant eggshell surface treatments for SE management. These treatments included a sanitizer called peracetic acid (PAA) and two probiotic treatments that colonize eggshells with beneficial bacteria.

Farmer Takeaways

Paracetic acid and probiotic sprays can both effectively reduce Salmonella Enteritidis (SE) populations on eggshell surfaces, and may be viable organic strategies for mitigating the transmission of SE at the egg and hatchling stages of development.
Probiotics significantly reduced Salmonella Enteritidis populations on the inner eggshell membrane and within developing embryos. The ability of probiotic bacteria to migrate through an eggshell and outcompete internal Salmonella bacteria is an important benefit over existing organic egg sanitation options.

Project Objectives and Approach

Evaluate several organic-compliant eggshell surface treatments, including peracetic acid (PAA) and probiotics, for their efficacy in reducing Salmonella Enteritidis prevalence on hatching eggs

Researchers at the University of Connecticut inoculated eggs with five strains of Salmonella.
- - Eggs were obtained from a certified Salmonella-free research flock of chickens.
  - A standardized inoculum was prepared from five pathogenic Salmonella isolates, cultured from both humans and chickens. The inoculum was applied to the surface of the eggs.
One hour after inoculation, eggs were sprayed with one of three organic-compliant SE treatments, which included:
1. 1. Peracetic Acid (PAA): A 4% PAA solution, representing a standard organic poultry industry treatment.
  2. Lactobacillus rhamnosus Probiotic (LR)
  3. Lactobacillus paracasei Probiotic (LP)
    - **Note: Both probiotic strains were obtained from the USDA NRRL culture collection (Peoria, IL), cultured individually, and applied as a spray treatment on the broader end of hatching eggs.
  4. Control: Untreated; eggs did not receive any SE treatment following inoculation.
Eggs were evaluated seven times over the course of 18 days (following treatment application). Researchers conducted microbial analyses of outer egg surfaces, inner shell surfaces, and internal egg contents, counting populations of both pathogenic and beneficial/probiotic (Lactobacillus) bacteria.
- On days 14 and 18, researchers also counted bacteria in different tissues within the growing embryos.

Key Findings

The application of probiotics (LR and LP), and paracetic acid (PAA) significantly reduced Salmonella Enteritidis populations on eggshell surfaces

Paracetic acid (PAA) rapidly reduced Salmonella Enteritidis (SE) populations on the surface of the eggs, with lower SE colony counts compared to all other treatments beginning the day of treatment application through 14 days post-application.
Both probiotic treatments reduced SE colony counts compared to the untreated control, beginning one day after application.
By Day 18, all three SE treatments (PAA, LR probiotic, and LP probiotic) had reduced SE presence on outer eggshell surfaces to undetectable levels. These findings indicate that paracetic acid and probiotic sprays can effectively reduce Salmonella Enteritidis populations on eggshell surfaces, and may be a viable organic strategy for mitigating the transmission of SE at the egg and hatchling stages of development.

Probiotics significantly reduced Salmonella Enteritidis populations on the inner eggshell membrane and within developing embryos

Both probiotic treatments reduced SE populations on inner shell membranes and within the egg’s internal contents (developing embryo), from Day 0 to Day 18.
Paracetic acid (PAA) was not as effective at reducing internal SE populations as either of the probiotic treatments, but did sometimes reduce SE when compared to the untreated control.
- - Probiotics function by outcompeting pathogenic bacteria (i.e., Salmonella Enteritidis) for nutrients and space. In this study, the researchers measured significant probiotic populations both inside and outside eggs. The ability of probiotic bacteria to migrate through an eggshell and outcompete internal Salmonella is an important benefit over existing organic egg sanitation options.
  - These findings indicate that probiotics may be a particularly promising organic management strategy for Salmonella Enteritidus transmission in hatcheries, providing external and internal protection against SE.

Resources

Kosuri, P., Muttathukonam, S. H., Reddyvari, R., Gao, M., Ren, Y., & Amalaradjou, M. A. (2025). Probiotic application reduces Salmonella Enteritidis contamination in layer hatching eggs and embryos. Poultry Science, 104(9), 105389.

Location

Connecticut

Collaborators

Praveen Kosuri, University of Connecticut
Sulthana Humayoon Muttathukonam, University of Connecticut
Ragini Reddyvari, University of Connecticut
Mairui Gao, University of Connecticut
Yuying Ren, University of Connecticut

Region

Northeast/Mid-Atlantic

Topic

Livestock Well-Being

Year Published

2025