Oleanolic acid combats Streptococcus iniae via cell membrane damage and oxidative stress, transcriptomic and...

Area of Science:

• Microbiology
• Aquatic Animal Health
• Pharmacology

Background:

• Streptococcus iniae causes significant economic losses in aquaculture.
• Oleanolic acid, a triterpenoid from Swertia mileensis, exhibits antibacterial properties.

Purpose of the Study:

• To investigate the antibacterial effect and mechanism of oleanolic acid against Streptococcus iniae DY2307.
• To explore oleanolic acid as a potential antibiotic alternative in aquaculture.

Main Methods:

• Phenotypic experiments including MIC/MBC determination, ATP production, ROS levels, and biofilm disruption.
• Transcriptome analysis (RNA-Seq) to identify differentially expressed genes (DEGs) and enriched pathways.
• KEGG pathway analysis to elucidate the molecular mechanisms of action.

Main Results:

• Oleanolic acid demonstrated minimum inhibitory concentration (MIC) of 16 μg/mL and minimum bactericidal concentration (MBC) of 32 μg/mL against S. iniae.
• Observed effects included cell membrane and wall disruption, decreased ATP, increased ROS, biofilm inhibition, and hindered protein synthesis.
• Transcriptomic analysis revealed downregulation of key metabolic pathways (PTS, glycolysis, TCA, PPP) and upregulation in systems like two-component systems and quorum sensing.

Conclusions:

• Oleanolic acid combats S. iniae primarily by inducing cell membrane damage and oxidative stress.
• The findings support oleanolic acid's potential as a natural antibiotic alternative for controlling S. iniae infections in aquaculture.
• Further research can build upon these findings for developing novel strategies against aquatic pathogens.