Pathogenic analysis of Andinoacara rivulatus skin ulcer disease caused by Klebsiella pneumoniae in China.

In July 2022, Andinoacara rivulatus developed an unexplained skin ulcer disease, which seriously affected its ornamental value in a farm in Liaoyang, Liaoning Province. A dominant strain AKP07 was isolated from the ulcer lesions, spleen, and liver tissues of diseased fish. The strain AKP07 was identified as Klebsiella pneumoniae by morphological, biochemical, and molecular analysis. The strain was multidrug-resistant and detected four virulence genes with WabG, uge, fimH, and mrkD. Following experimental challenge, symptoms similar to natural infection appeared, and a similar strain was isolated. Histopathological observations showed that the strain mainly targeted the gills, spleen, and liver. The main pathological changes included gill lamellar deformation, epithelial cell hyperplasia, spleen congestion, and liver vascular injury, with the degree of pathological changes related to the dose of infection. This study indicates that K. pneumoniae AKP07 is the pathogen of A. rivulatus skin ulcer disease, which is a typical dose-related opportunistic pathogen. [ABSTRACT FROM AUTHOR]