Evaluation of Antibiotic-Sensitive Bacillus Strain as a Potential Probiotic for Enhanced Growth in Penaeus vannamei.

The safety of probiotics in aquaculture, particularly concerning the transfer of antibiotic resistance genes (ARGs), has become a significant concern. This study aims to isolate antibiotic-sensitive Bacillus strains from the gut of Penaeus vannamei and evaluate the potential for practical application in shrimp farming. The strain was tested for antibiotic sensitivity to 10 commonly used antibiotics, and the minimum inhibitory concentration (MIC) values were determined. Morphological analysis and 16S rRNA sequencing confirmed its identity. The probiotic properties, antibacterial activity, and feeding effects on P. vannamei were also assessed. The results showed that Bacillus sp. J3 and Lysinibacillus sp. R4 were generally sensitive to antibiotics but resistant to sulfapyridine and ciprofloxacin. Both strains exhibited acid and bile salt resistance in vitro and performed well in extracellular hydrolase tests. J3 demonstrated co-coagulation effects against Aeromonas veronii, Vibrio parahaemolyticus, and Vibrio alginolyticus, with coagulation rates over 35%, while R4 showed the highest co-coagulation rate (47%) against V. alginolyticus. Both strains exhibited strong antibacterial activity, with inhibition zones ranging from 20 to 22.5 mm. Preliminary shrimp farming tests showed that R4 improved shrimp growth and survival rates compared to the control, and its combination with Bacillus coagulans resulted in even greater efficacy. These findings suggest that Lysinibacillus sp. R4 holds promise as a probiotic for enhancing P. vannamei growth, and future research could explore the use of multiple probiotic combinations in aquaculture.