Marine Microalgae Schizochytrium sp. S31: Potential Source for New Antimicrobial and Antibiofilm Agent

Background: The rise of antibiotic-resistant bacteria necessitates the discovery of new, safe, and bioactive antimicrobial compounds. The antibacterial and antibiofilm activity of microalgae makes them a potential candidate for developing natural antibiotics to limit microbial infection in various fields. Objective: This study aimed to analyze the antibacterial effect of the methanolic extract of Schizochytrium sp. S31 microalgae by broth microdilution and spot plate assays. Methods: The antibacterial effects of Schizochytrium sp. S31 extract was studied on gramnegative pathogens, Pseudomonas aeruginosa, Escherichia coli 35218, Klebsiella pneumonia, which cause many different human infections, and the gram-positive pathogen Streptococcus mutans. At the same time, the antibiofilm activity of the Schizochytrium sp. S31 extract on Pseudomonas aeruginosa and Escherichia coli 35218 bacteria were investigated by crystal violet staining method. Results: Schizochytrium sp. S31 extract at a 60% concentration for 8 hours displayed the highest antibacterial activity against P. aeruginosa, E. coli 35218, and K. pneumonia, with a decrease of 87%, 92%, and 98% in cell viability, respectively. The experiment with Streptococcus mutans revealed a remarkable antibacterial effect at a 60% extract concentration for 24 hours, leading to a notable 93% reduction in cell viability. Furthermore, the extract exhibited a dose-dependent inhibition of biofilm formation in P. aeruginosa and E. coli 35218. The concentration of 60% extract was identified as the most effective dosage in terms of inhibition. Conclusion: This research emphasizes the potential of Schizochytrium sp. S31 as a natural antibacterial and antibiofilm agent with promising applications in the pharmaceutical sectors. This is the first study to examine the antibacterial activity of Schizochytrium sp. S31 microalgae using broth microdilution, spot plate assays, and the antibiofilm activity by a crystal staining method. The findings of this study show that Schizochytrium sp. S31 has antibacterial and antibiofilm activities against critical bacterial pathogens.