Pathological changes of highly pathogenic on .

An outbreak of a disease with a high mortality rate occurred in a Chinese Softshell Turtle () farm in Hubei Province. This study isolated a highly pathogenic strain (Y271) from diseased . Y271 has hemolysis, containing both Hemolysin BL (, and ), Non-hemolytic enterotoxin, NHE (, and ), and Enterotoxin FM () genes. Y271 is highly pathogenic against with an LD = 6.80 × 10 CFU/g weight. was detected in multiple tissues of the infected . Among them, spleen tissue showed the highest copy number density (1.54 ± 0.12 × 10 copies/mg). Multiple tissues and organs of diseased exhibited significant pathological damage, especially the spleen, liver, kidney, and intestine. It showed obvious tissue structure destruction, lesions, necrosis, red blood cells, and inflammatory cell infiltration. proliferating in the spleen, liver, and other tissues was observed. The intestinal microbiota of the diseased was altered, with a greater abundance of Firmicutes, Fusobacterium, and Actinomyces than in the healthy group. , , and abundance were higher in the diseased group than in the healthy group. The number of unique microbial taxa (472) in the disease group was lower than that of the healthy group (705). Y271 was sensitive to multiple drugs, including florfenicol, enrofloxacin, neomycin, and doxycycline. is the etiological agent responsible for the massive death of and reveals its potential risks during cultivation.