Identification and biological characterization of the novel pathogen responsible for cataract in bullfrogs

To investigate the cause of the large-scale death of farmed bullfrog (Lithobates catesbeianus) in a certain area of Hubei Province. Bacterial isolates were revealed from the liver, brain, and lung of bullfrogs exhibiting typical symptoms of cataract. Regression infection studies confirmed that a strain Z20240301 was responsible for the white eyes and high mortality rate among bullfrogs. Histopathological analysis revealed that the infection could lead to varying degrees of hemorrhage in the meningeal connective tissue of the bullfrogs. The further 16S rRNA sequence identification and Genome-wide analysis confirmed that the Z20240301 belongs to Acinetobacter johnsonii, which carries 566 virulence factor-related genes, include hlyA, hlyB, and lipopolysaccharide (LPS); and 257 drug resistance-related genes, including those conferring resistance to major antibiotic classes such as macrolides, aminoglycosides, fluoroquinolones, and tetracyclines. The isolate Z20240301 was highly sensitive to cefazolin oxime, cefradine, gentamicin, streptomycin, netilmicin, and tobramycin; moderately sensitive to cefotaxime, azithromycin, erythromycin, enrofloxacin, doxycycline, and neomycin; and resistant to enoxacin, norfloxacin, and kanamycin. This study is the first to confirm A. johnsonii as a causative agent of cataracts in bullfrogs, providing a new theoretical basis for the diagnosis, prevention, and treatment of this disease.