患病杂交鲟鲟疱疹病毒3型与海豚链球菌的共检出、病理特征及药敏分析OA

[Objective]In late July 2025,an outbreak of acute mortality occurred in cultured Siberian hybrid sturgeon(Acipenser baerii ♀×A.schrenckii ♂)in Ya'an,Sichuan Province,characterized by extensive cu-taneous and visceral hemorrhages.This study aims to identify the etiological agents and characterize the histo-pathological lesions to provide a scientific basis for clinical diagnosis and disease control of A.baerii ♀×A.schrenckii ♂.[Methods]One moribund A.baerii ♀×A.schrenckii ♂ exhibiting typical clinical signs was randomly collected from each of the six affected ponds(n=6,S1-S6).Tissues from the liver,spleen,kidney,and brain were sampled for bacterial isolation,viral polymerase chain reaction(PCR)detection,and histopathologi-cal examination.Molecular biological identification of the isolated strains was performed using 16S rDNA sequence analysis.Simultaneously,the major capsid protein(MCP)gene of acipenserid herpesvirus 3(AciHV-3)was amplified and sequenced for phylogenetic analysis.Antimicrobial susceptibility testing(AST)was conduc-ted on the recovered bacterial isolates.[Results]Viral detection confirmed that all six samples were positive for AciHV-3;phylogenetic analysis showed that the MCP gene sequences clustered closely with reference strains within a single clade.Regarding bacterial isolation,morphologically identical Gram-positive cocci were recovered from four of the six samples(4/6).The 16S rDNA sequence analysis of the representative strain(Gen-Bank accession no.PX427207)showed 99%identity with that of Streptococcus iniae in GenBank.In the phylo-genetic tree constructed based on 16S rDNA sequences,the isolate clustered into a single clade with S.iniae.Therefore,the isolate was eventually identified as S.iniae.Antimicrobial susceptibility testing revealed signific-ant variation among the isolated strains.In the eight-antimicrobials susceptibility test,only cefotaxime exhibi-ted potent inhibitory activity against all isolates.Susceptibility to florfenicol,doxycycline,enrofloxacin,and ciprofloxacin fluctuated markedly across strains,with the majority being intermediate or resistant.Furthermore,all isolates demonstrated complete resistance to amoxicillin,sulfamethoxazole/trimethoprim,and neomycin sulfate,exhibiting a pronounced multidrug resistance(MDR)phenotype.Histopathological analysis revealed ex-tensive necrosis,hemorrhage,and inflammatory infiltration across multiple organs.[Conclusion]This study confirms the co-detection of AciHV-3 and S.iniae in cultured sturgeon in Sichuan.Given the severe and con-sistent histopathological damage,these findings suggest that the high-mortality outbreak was likely driven by the synergy of AciHV-3 and S.iniae.This research provides essential data for the clinical monitoring and man-agement of AciHV-3.