Proliferative enterocolitis associated with dual infection with enteropathogenic Escherichia coli and Lawsonia intracellularis in rabbits

Abstract

Both enteropathogenic Escherichia coli (EPEC) and an obligate intracellular bacterium, previously referred to as an intracellular Campylobacter-like organism and now designated Lawsonia intracellularis, have been reported as causes of enterocolitis in rabbits. An outbreak of enterocolitis in a group of rabbits, characterized by an unusually high rate of mortality, was found to be associated with dual infection with EPEC and L. intracellularis. The EPEC strain was found to have eaeA gene homology but was negative for afrA homology. The absence of the afrA gene, which encodes the structural subunit for the AF/R1 pilus, indicates that this rabbit EPEC strain is distinct from the prototypic RDEC-1 strain. This finding suggests that rabbit EPEC strains widely reported in Western Europe, which lack AF/R1 pili, are also present in rabbits in the United States. Dual infection with these two pathogens in rabbits has not been previously reported and may have contributed to the unusually high mortality observed in this outbreak.

FIG. 1

Photomicrograph of a section of small intestine from a rabbit with proliferative enterocolitis. The mucosa of the intestine has blunted villi, a moderate inflammatory cell infiltrate, and a decreased number of goblet cells. The crypt epithelial cells are markedly hyperplastic. Hematoxylin and eosin stain was used (magnification, ×40).

FIG. 2

Photomicrograph of mucosal detail of a section of small intestine from a rabbit with proliferative enterocolitis, demonstrating typical AE lesions on surface intestinal epithelial cells. Hematoxylin and eosin stain was used (magnification, ×1,000).

FIG. 3

Photomicrograph of a section of small intestine from a rabbit with proliferative enterocolitis, demonstrating numerous curved- to spiral-shaped bacteria in the apical cytoplasm of the intestinal epithelial cells. Modified Warthin-Starry silver stain was used (magnification, ×1,000).

FIG. 4

Southern blot of HindIII-digested genomic DNA from E. coli strains probed with the eaeA gene probe under conditions of high stringency. The lanes contain independent isolates from four rabbits with dual infections with EPEC and L. intracellularis, RDEC-1, and a nonpathogenic E. coli K-12 strain.