Minimum Intestinal Inoculum for Nurmi Cultures and a New Method for Determining Competitive Exclusion of Salmonella...

Area of Science:

• Avian health
• Microbiology
• Gastrointestinal immunology

Background:

• Salmonella infections pose a significant threat to poultry health and food safety.
• Probiotics and beneficial gut microbiota are explored for disease prevention in livestock.
• Nurmi cultures, derived from adult chicken intestinal material, have shown potential in conferring protection.

Purpose of the Study:

• To evaluate the efficacy of orally administered Nurmi cultures in protecting chicks against Salmonella infection.
• To determine the minimum effective dose of intestinal material required for Nurmi culture preparation.
• To develop and validate a simplified method for enumerating nalidixic acid-resistant Salmonella in chick cecal content.

Main Methods:

• Nurmi cultures were prepared by inoculating varying amounts (10^-1 to 10^-11 g) of adult chicken intestinal material into anaerobic liquid medium and incubating for 3 days at 37°C.
• Chicks were orally administered the prepared Nurmi cultures and subsequently challenged with nalidixic acid-resistant (Nal⁺) Salmonella.
• Enumeration of Nal⁺ Salmonella in chick cecal content was performed 7 days post-treatment using a newly developed swab-plate method.

Main Results:

• Excellent protection against Salmonella challenge was achieved with Nurmi cultures initiated with as little as 10^-7 g of intestinal material.
• A dose-dependent reduction in protection was observed with lower initiation amounts (10^-8 to 5 × 10^-10 g), with no protection from 10^-10 g.
• The developed swab-plate method provides accurate (± 1 log₁₀) and efficient enumeration of Nal⁺ Salmonella in the range of 10¹ to 10⁷ organisms per gram.

Conclusions:

• Oral administration of Nurmi cultures is an effective strategy for protecting chicks against Salmonella infection.
• The efficacy of Nurmi cultures is dependent on the quantity of intestinal material used for their preparation.
• The novel swab-plate method simplifies Salmonella enumeration, offering a practical tool for research and potentially for monitoring gut health in poultry.