Screening of Antibiotic-Sensitive Lactic Acid Bacteria (LAB) Associated with the Gut of Penaeus Vannamei and its...

The increasing use of antibiotics in shrimp aquaculture has raised concerns regarding ecological safety and the emergence of antibiotic resistance. This study aimed to isolate and characterize probiotic lactic acid bacteria (LAB) strains from the gut of Penaeus vannamei to evaluate their potential as antibiotic alternatives in aquaculture. Two strains, S1 and S2, were identified with 99.79 and 99.51% similarity to Pediococcus acidilactici DSM 20284 and Enterococcus lactis BT159, respectively. Based on minimum inhibitory concentration (MIC) assays, both strains exhibited high sensitivity to the tested antibiotics. They also demonstrated notable acid and bile salt tolerance, with S1 maintaining a survival rate of 30% at pH 5 and S2 achieving 40% survival at pH 6. Under 0.03% bile salt concentration, survival rates were approximately 60% (S1) and 45% (S2), while S1 retained 15% viability even at 0.9% bile salt. Enzymatic activity analysis indicated that both strains exhibited lower amylase activity compared to other hydrolytic enzymes, with S2 showing higher cellulase and protease activities than S1. Antimicrobial assays revealed that both strains exerted broad-spectrum inhibition against four indicator pathogens. S1 exhibited the strongest inhibitory effect against Aeromonas hydrophila (inhibition zone: 1.6-2.2 cm), whereas S2 showed the highest inhibition against Vibrio parahaemolyticus (1.5-2.4 cm). Feeding trials demonstrated that the combined application of S1 and S2 significantly enhanced shrimp body weight (6.05 ± 0.09 g vs. 9.23 ± 0.2 g, P < 0.01) and survival rate (62.49% ± 1.56 vs. 93.78% ± 2.55, P < 0.01). These findings highlight the potential of Lactobacillus strains as probiotics in shrimp farming, offering a sustainable approach to reducing antibiotic dependency and improving shrimp health and productivity.