A Pathogenic Providencia rettgeri Isolated and Identified from Pelodiscus sinensis

The infectious diseases have become more frequent with the production of farmed Chinese soft-shelled turtles (Pelodiscus sinensis) increasing. In this study, bacterial strain was isolated, identified, and characterized from the liver of diseased Chinese soft-shelled turtles exhibiting body surface hemorrhages, claws and tail tips necrosis, and bleeding spots in visceral tissues. Based on the analysis results of morphology, biochemistry, and 16S ribosomal RNA (16S rRNA) sequencing, one bacterium Providencia rettgeri (P. rettgeri) was identified. The histopathological examination results revealed varying degrees of tissue damage in the spleen, liver, kidneys, and intestines of individuals with P. rettgeri. Challenge experiments results confirmed that the P. rettgeri caused morbidity and mortality in healthy Chinese soft-shelled turtles, reproducing similar clinical symptoms of naturally infected individuals. And, its mortality rate was up to 91% in the highest concentration group. Screening of eight virulence-associated genes results revealed that this P. rettgeri strain carried virulence factors including invasion protein gene, alpha-hemolysin, and others which were considered to contribute to pathogenicity. Antibiotic susceptibility testing showed that the bacterium was sensitive to amikacin and ciprofloxacin, which may be effective therapeutic options. In conclusion, this bacterium P. rettgeri was the pathogen that caused this disease in Pelodiscus sinensis. These results provide valuable research basis for the disease prevention and control of Pelodiscus sinensis farming.