Isolation, identification, and fermentation condition optimization of a marine bacterial strain W52 against Candida albicans

Abstract:

[Background] The current misuse of antibiotics has exacerbated the issue of pathogen resistance, rendering marine microorganisms a focal point of research due to their novel bioactive metabolites. [Objective] a strain resistant to Candida albicans was screened and identified from the bacterial strains in the Arctic Ocean sediment. The fermentation conditions of this strain were optimized, and the antimicrobial activity of the crude fermentation extract was evaluated. [Methods] Among the strains from Arctic sea mud, a strain with the best antibacterial effect against Candida albicans was selected through the plate confrontation method and the agar diffusion method. With the diameter of the inhibition zone obtained by agar diffusion method as the indicator, single factor test, orthogonal test, and response surface method were employed to optimize the medium formula and fermentation conditions. The crude extract was obtained by fractional precipitation with hydrochloric acid and methanol extraction. The results of agar diffusion assay demonstrated inhibitory effects of the strain against six pathogens. [Results] A strain W52 with the strongest antibacterial effect against Candida albicans was identified as Bacillus subtilis. The optimal medium formula consisted of 5 g/L glucose, 1 g/L peptone, and 2 g/L NaCl, and the optimal fermentation conditions were fermentation at 36 ℃, initial pH 6.5, and 178 r/min for 75 h. After optimization, the diameter of the inhibition zone increased significantly from 18.43 mm to 30.23 mm. [Conclusion] B. subtilis W52 has inhibitory effects on C. albicans, Candida auris, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and Salmonella typhimurium. This study provides a theoretical basis for the development of antimicrobial agents derived from marine microorganisms.