Profiling of Egg Layer Flocks Affected with Focal Duodenal Necrosis Based on a Questionnaire Survey

Laser Capture Microdissection, Culture Analysis, and Bacterial Sequencing to Evaluate the Microbiota of Focal Duodenal Necrosis in Egg Layers

Focal duodenal necrosis (FDN) is a common intestinal disease of table egg layers. In this research we aimed to identify the bacteria commonly found in FDN lesions as seen with histopathological analysis. Fifty-nine ethanol-fixed duodenum samples were collected from egg layers on eight FDN-affected farms, and 42 samples had typical FDN lesions. Excision of bacteria-containing lesions using laser capture microdissection was performed, followed by 16S rRNA gene sequencing of extracted DNA for bacterial identification. Bacterial sequencing analysis revealed no consistent bacterial species identified from samples with FDN. However, analysis of the relative phylum abundance revealed differences in the duodenal microbiota between layers with FDN and healthy birds. There were differences in the abundance of Proteobacteria, Firmicutes, and Actinobacteria between FDN-positive and FDN-negative control samples compatible with intestinal dysbiosis. In addition, 10 duodenal samples with FDN lesions were collected for bacteriological analysis, yielding 47 colonies on tryptone soy agar, MacConkey agar, and blood agar plates. Using 16S rRNA gene PCR, 39/47 (53.8%) colonies were identified as Escherichia coli. PCR for E. coli virulence genes identified 21/39 (53.8%) E. coli isolates as avian pathogenic E. coli-like. PCR analysis for 19 E. coli virulence genes associated with intestinal disease strains including inflammatory bowel disease found 11/39 (28.2%) isolates containing more than 10 of these virulence genes. In conclusion, FDN appears to be a multifactorial inflammatory intestinal disease associated with intestinal dysbiosis, and Gram-negative bacteria including E. coli may contribute to the pathogenesis of this disease.

Focal duodenal necrosis in chickens: attempts to reproduce the disease experimentally and diagnostic considerations

Focal duodenal necrosis (FDN) is an intestinal disease of egg-layer chickens characterized by multifocal necrosis of the duodenal loop and proximal jejunum. Affected flocks usually have decreased egg weights and drops in egg production. Previous studies have associated this condition with Clostridium perfringens infection. We tried to reproduce FDN by experimental infection of egg-laying chickens using different netB-positive and netB-negative C. perfringens strains, and duodenal homogenate obtained from FDN lesions. Chickens challenged with C. perfringens and/or duodenal homogenate developed duodenitis after challenge. Gross lesions included mucosal erosions, hyperemia, mucosal hemorrhages, and watery intestinal content. Microscopic lesions included mild enterocyte degeneration and necrosis, and mild-to-moderate hemorrhage and lymphoplasmacytic and heterophilic infiltration of the lamina propria. Two netB-positive C. perfringens strains closely related to necrotic enteritis pathogenic strains, by genomic composition, were re-isolated from lesions. Necrosis of intestinal crypts was observed in chickens challenged with duodenal homogenate with or without C. perfringens coinfection. Characteristic microscopic FDN lesions with significant necrosis and loss of villus enterocytes were not reproduced.