CNS viral diseases have resulted in many deadly epidemics throughout history and continue to pose one of the greatest threats to public health. Drug therapy remains challenging due to the complex structure and relative impermeability of the biological tissues and barriers.

In the study, a comprehensive investigation on potential bacterial pathogens affecting largemouth bass (Micropterus salmoides) was performed. Monthly surveys were conducted from April to October 2024. Diseased largemouth bass exhibited diverse clinical symptoms, such as rot of gill and fin, ulcers on body surface, and petechial hemorrhages in liver. Following isolation and identification, a total of 21 potential bacterial pathogens (numbered strain 1 to 21, respectively) were identified. The genus Aeromonas had the highest proportion (67.14%), among which the frequency of Aeromonas veronii was 24.60%. TEM analysis revealed that the bacterial strains exhibited three predominant shapes (rod-shaped, spherical, and curved) with length ranging from 0.5 to 3 μm. Flagellar structures were observed in strains 1–4, 6–8, 11–17, and 19–21, with variations in number and growth sites. Three isolates (strains 9, 10, 18) demonstrated Gram-positive characteristic, and strains 5, 11, and 18 have capsule structures. Strains 5, 9, 10, and 18 were non-motile, and strains 1–4, 6, 7, 9–11, 16–18, and 21 exhibited β-hemolysis. Physiological and biochemical characteristics of the 21 bacterial isolates were comprehensively analyzed. Antibiotic sensitivity testing revealed that florfenicol and enrofloxacin exhibited excellent antibacterial effects. These data will enrich the potential bacterial diseases information and promote the healthy development of the largemouth bass industry.

Bacterial infections represent a major constraint to largemouth bass (Micropterus salmoides) aquaculture; safe and sustainable alternatives to conventional antibiotics are needed. This study aimed to screen, characterize, and evaluate host-derived intestinal probiotics from healthy largemouth bass for bacterial disease biocontrol. A total of 68 intestinal bacterial strains were isolated and screened for antagonistic activity against 21 bacterial pathogens previously isolated from diseased largemouth bass. Five isolates with stable inhibitory activity were identified as Plesiomonas shigelloides (MS-24), Aeromonas dhakensis (MS-26), Lactococcus lactis (MS-54), Bacillus subtilis (MS-67), and Bacillus paranthracis (MS-68) by 16S rRNA and gyrB gene sequencing. Morphological characteristics, physiological and biochemical profiles, and growth kinetics of the 5 isolates were assessed. Among them, only MS-54 and MS-67 exhibited non-hemolytic phenotypes and low in vivo toxicity, with host mortality rates of 0.00% and 1.11%, respectively. In challenge trials, dietary supplementation with MS-54, MS-67, or their combination reduced cumulative mortality to varying degrees. Significant protection was observed against V. alginolyticus and A. jandaei, and the highest relative percent survival (RPS) was 22.62% in the MS-54 + MS-67 group after A. jandaei challenge. Results so far indicated that Lactococcus lactis MS-54 and Bacillus subtilis MS-67 are promising host-derived probiotic candidates with good antagonistic activities, providing potential strategies for bacterial disease biocontrol and sustainable management in largemouth bass aquaculture.