Isolation, identification, and pathogenicity analysis of <i>Staphylococcus epidermidis</i> in Chinese soft-shelled turtles

In this study, a dominant bacterial strain was isolated from diseased Chinese soft-shelled turtles (CSSTs) ( Pelodiscus sinensis ) reared at an aquaculture farm in Hubei Province. Its pathogenic characteristics and virulence were investigated. Based on morphological observation, 16S rRNA gene sequence analysis, and physiological and biochemical characterization, the isolate was identified as Staphylococcus epidermidis . This isolate harbored virulence genes associated with adhesion and biofilm formation, including icaA (intercellular adhesion gene A), bhp (biofilm-associated hydrophobin-like protein) and clfA (clumping factor A), and exhibited a median lethal dose (LD50) of 8.99×10³ CFU/g weight in CSSTs. Additionally, antibiotic susceptibility testing revealed that the strain was sensitive to gentamicin, doxycycline, florfenicol, neomycin, enrofloxacin, and cefotaxime. Infected CSSTs displayed varying degrees of pathological changes in the intestine, kidneys, spleen, and liver. Moreover, the expression levels of immune-related genes MAP2K6, MyD88, and TLR8 were significantly upregulated in internal organs. Overall, these results indicate that infection with S. epidermidis can lead to significant mortality in CSSTs. This study provides scientific reference for the detection and control of S. epidermidis infections in CSSTs.