To investigate the effect and underlying mechanism of ethyl acetate extract from Lactiplantibacillus plantarum Z139 on the single- and mixed-species biofilms of Escherichia coli and Staphylococcus aureus.

The minimum inhibitory concentrations (MICs) of the extract against single and mixed cultures were determined using the two-fold broth dilution method. We investigated the effect of the extract on the formation of single and mixed-species biofilms by E. coli and S. aureus, the eradication of mature biofilms, cell membrane permeability, bacterial nucleic acid leakage, extracellular polysaccharide production, and bacterial survival in biofilms.

The MIC of the extract against S. aureus, E. coli and mixed cultures was 3.2 mg/ml. When incubated at the sub-inhibitory concentration (1/2 MIC, 1.6 mg/ml) for 24 h, the inhibition rates against the single- and mixed-species biofilms of S. aureus and E. coli were 49.70%, 51.36%, and 50.94%, respectively, while eradication rates after 48 h incubation at 12.8 mg/ml were 65.55%, 75.26%, and 65.56%, respectively. In addition, the extract effectively inhibited extracellular polysaccharide production.

The extract exhibits strong inhibitory effects on E. coli, S. aureus, and their mixed cultures, suggesting its potential as a novel lactic acid bacteria-derived biocontrol agent against mixed biofilms. This study provides data support for the prevention and control of pathogenic biofilm contamination and the development of novel antibacterial agents.