Growth and probiotic properties of Lactobacillus plantarum HY21 from intestinal tract of Apostichopus japonicus

Abstract:

【Objective】 To search for the strains with improved tolerance, probiotic properties, and safety, we isolated Lactobacillus plantarum HY21 from the intestinal contents of Apostichopus japonicus and evaluated the probiotic potential of the strain. 【Methods】 The shake flask fermentation, environmental factor simulation test, and antibiotic susceptibility test were carried out to study the growth characteristics and acid production of the strain, as well as the antioxidant capacity and aquatic pathogen-inhibiting effects of the fermentation broth. In addition, L. plantarum HY21 was characterized in terms of the tolerance to environmental factors, hydrophobicity, auto-agglutination and co-aggregation, antibiotic susceptibility, and intestinal adhesion ability. 【Results】 L. plantarum HY21 in shake flask culture with the initial pH 8.0 entered the logarithmic growth during the period of 2–10 h. The culture showed a strong acid-producing ability with the minimum pH 3.6 at the time point of 18 h. The fermentation broth of the strain showed an inhibition zone diameter of (13.96±0.30) mm against Vibrio alginolyticus and a 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) free radical scavenging rate of 95.45%±1.56%. L. plantarum HY21 had a hydrophobicity rate of 60.42%±2.78%, an auto-agglutination rate of 22.69%±1.36% and a co-aggregation rate of 27.98%±1.45% with V. alginolyticus. Furthermore, the strain showed the adhesion number of (1.66±0.01)×10⁶ CFU/mL and (1.23±0.15)×10⁶ CFU/mL to fish body surface and intestinal mucus protein, respectively. L. plantarum HY21 was susceptible to 13 common antibiotics. The survival rate of L. plantarum HY21 reached 99% and above in simulated gastrointestinal fluid (pH 3.0, pH 6.8) within 3 h, 68.11%±7.98% in 10% fish bile fluid within 3 h, and 97.58%±7.14% in 3% sea salt solutions within 16 h. 【Conclusion】 L. plantarum HY21 is a probiotic strain with strong colonization potential, antimicrobial activity, and antioxidant capacity, demonstrating a high survival rate and high safety in the applied environment. The findings provide a theoretical basis for the development of new probiotic strains as probiotic additives for aquaculture.