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

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Abstract
Protection of chicks against Salmonella infection was obtained by oral administration of Nurmi cultures. The Nurmi cultures were prepared by inoculating adult chicken intestinal material (10−1 to 10−11 g) into anaerobic liquid medium and incubating for 3 d at 37°C. Excellent protection was obtained with cultures initiated with as little as 10−7 g of fecal or cecal content; progressively less protection with 10−8 to 5 × 10−10 g; and none with cultures initiated with 10−10 g. Protection was based on challenge of treated chicks with nalidixic acid-resistant (Nal+) Salmonella and enumeration of the Nal+ organisms in the chick cecal content 7 d later. To simplify the enumeration, a swab-plate method was developed. The method saves time and materials and gives relatively accurate (± 1 log10) determinations of Nal+ Salmonella over the range of 101 to 107 per g of cecal content.