Morganella morganii, a bacterial pathogen in diseased Chinese soft-shelled turtles (Pelodiscus sinensis)

The Chinese Soft-Shelled Turtle (CSST) is a significant commercial aquatic animal in China. However, the increased frequency of diseases in the breeding process has hindered industrial development. A gram-negative bacterium, Z617 strain, was isolated from diseased CSST on a farm in Hubei Province, China. It was identified as Morganella morganii by 16S rDNA. The median lethal dose of Z617 strain was (8.32 ± 0.09) × 104 colony-forming units/g CSST weight. The histopathological changes of infected CSSTs, including hepatic sinus congestion, vacuolization of hepatocytes, ulceration of the intestinal mucosa, destruction of the intestinal villi, an unclear distinction between red and white pulp of the spleen, and swelling and necrosis of the glomerular of the kidney, were examined. The structure of the intestinal community of CSSTs was analyzed, and the distinction between richness and diversity was found. The intestinal microbiota community structure differed between the control and infected groups. The relative abundance of Cetobacterium, Lawsonia, and Bacteroides was increased in the infected group compared with the control group at the genus level. Z617 strain is susceptible to antibiotics such as Ceftazidime and Piperacillin. Moreover, it showed various degrees of drug resistance to Enrofloxacin, Doxycycline, Cefuroxim, Streptomycin, Midecamy Cinum, Minocycline, Gentamicin, Neomycin, Florfenicol, and Carbenicillin. This research indicated that M. morganii handled numerous CSSTs' death and clarified the biological profile and potential mechanisms of the Z617 strain. It throws some light on the disease diagnosis and may provide the referenced value for disease treatment.