Characterization of Intestinal Microbiota in Lambs with Different Susceptibility to F17.

Diarrhea is one of the most commonly reported diseases in young farm animals. () F17 is one of the major pathogenic bacteria responsible for diarrhea. However, the pathogenicity of diarrhea in lambs involving F17 strains and how F17 infection modifies lambs' intestinal microbiota are largely unknown. To evaluate diarrhea in newborn lambs with an infection of F17, 50 lambs were selected for challenge experiments and divided into four groups, namely, a high-dose challenge group, low-dose challenge group, positive control group, and negative control group. The F17 challenge experiments caused diarrhea and increased mortality in the experimental lamb population, with a higher prevalence (90%), mortality (35%), and rapid onset time (4-12 h) being observed in the high-dose challenge group than the results observed in the low-dose challenge group (75%, 10%, 6-24 h, respectively). After the challenge experiment, healthy lambs in the high-dose challenge group and severely diarrheic lamb in the low-dose challenge group were identified as lambs sensitive/resistant to F17 ( F17 -resistant/-sensitive candidate, AN/SE) according to the histopathological detection. Results of intestinal contents bacteria plate counting revealed that the number of bacteria in the intestinal contents of SE lambs was 10-fold greater than that of the AN lambs, especially in the jejunum. Then, 16S rRNA sequencing was conducted to profile the intestinal microbiota using the jejunal contents, and the results showed that SE lambs had higher and a lower ratio and intestinal microbiota diversity in the jejunum than AN lambs. Notably, high abundance of was revealed in AN lambs, which indicated that may serve as a potential probiotic for F17 infection. Our study provides an alternative challenge model for the identification of F17-sensitive/-resistant lambs and contributes to the basic understandings of intestinal microbiota in lambs with different susceptibilities to F17.