Evidence of Bacterial Co-Infection in Endangered Yangtze Sturgeon (Acipenser dabryanus)

Simple SummaryIn 2024 summer, the endangered Yangtze sturgeon in China suffered large-scale deaths, which was an urgent problem to solve. This study aimed to identify the cause of the disease and provide a basis for protecting the Yangtze sturgeon and preventing such diseases. The findings revealed that the bacterial co-infection (Streptococcus iniae, Klebsiella pneumoniae, Edwardsiella tarda, and Bacillus cereus) triggered by high temperature and high humidity environmental stress was closely related to this large-scale death event. And these bacteria all exhibited resistance to commonly used antibiotics in aquaculture. This was the first time multiple bacterial co-infection was found in Yangtze sturgeon, so protection should shift from focusing on a single bacterium to multiple ones, and ecological prevention measures are needed. These findings help protect this rare species, guide disease prevention in aquaculture, and safeguard aquatic ecological security.The Yangtze sturgeon (Acipenser dabryanus) is designated as critically endangered in the IUCN Red List and is a first-class protected species in China. During the summer of 2024, it suffered lethal disease outbreaks. Comprehensive pathological and microbiological analyses were conducted to clarify the etiology. Clinically, infected sturgeon exhibited systemic manifestations including cutaneous ulcers, hemorrhagic septicemia, and diffuse necrosis in liver, kidney and heart tissues. Histopathologically, infected sturgeon showed liver hepatocyte vacuolation/necrosis, renal glomerular atrophy, and cardiac epicardial thickening with lymphocyte/eosinophil infiltration; Gram staining revealed co-localized Gram-positive/negative bacteria in lesions, and TEM identified diverse bacterial morphotypes. Through isolation and molecular identification, four bacterial pathogens were characterized:Streptococcus iniae,Klebsiella pneumoniae,Edwardsiella tarda, andBacillus cereus.Bacterial load detection revealed the presence of these pathogens in lesion tissues. Antimicrobial susceptibility testing indicated multidrug resistance to florfenicol, tetracycline, and ampicillin (commonly used antibiotics in aquaculture), while high sensitivity to ceftazidime, ceftriaxone, and ciprofloxacin was observed. Thus, we infer that sustained high-temperature stress triggered bacterial co-infection is closely related to this large-scale death incident. This is the first evidence of polymicrobial infection in the Yangtze sturgeon, emphasizing the significance of shifting from a single-pathogen perspective to a multi-pathogen framework, and highlighting the urgency of implementing ecological prevention strategies for this species.