Characterization of Intestinal Microbiota in Lambs with Different Susceptibility to Escherichia coli F17

Escherichia coli (E. coli) F17 is one of the major pathogenic bacteria responsible for diarrhea in farm animals; however, little is known about the effect of E. coli F17 infection on the intestinal microbiota. The aim of this study was to investigate the intestinal microbiota in lambs with different susceptibilities to E. coli F17. By conducting an E. coli F17 challenge experiment, lambs sensitive/resistant (SE/AN) to E. coli F17 were identified, and 16S rRNA gene sequencing was performed to evaluate the intestinal microbiota in SE/AN lambs. The results showed that a relatively higher level of richness and diversity were characterized in the bacterial communities in the AN lambs than in the SE lambs, while the abundance of Lactococcus and Megasphaera elsdenii was found to be significantly different between the AN and SE lambs. Furthermore, our results indicated that the Bacteroidetes:Firmicutes ratio can serve as a promising bacterial biomarker for E. coli F17 infection. Our results can help in the development of new insights for the treatment of farm animals infected by E. coli F17. Diarrhea is one of the most commonly reported diseases in young farm animals. Escherichia coli (E. coli) F17 is one of the major pathogenic bacteria responsible for diarrhea. However, the pathogenicity of diarrhea in lambs involving E. coli F17 strains and how E. coli F17 infection modifies lambs' intestinal microbiota are largely unknown. To evaluate diarrhea in newborn lambs with an infection of E. coli 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 E. coli 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 E. coli F17 (E. coli 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(2 similar to 3)-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 Lactococcus and a lower Bacteroidetes:Firmicutes ratio and intestinal microbiota diversity in the jejunum than AN lambs. Notably, high abundance of Megasphaera elsdenii was revealed in AN lambs, which indicated that Megasphaera elsdenii may serve as a potential probiotic for E. coli F17 infection. Our study provides an alternative challenge model for the identification of E. coli F17-sensitive/-resistant lambs and contributes to the basic understandings of intestinal microbiota in lambs with different susceptibilities to E. coli F17.