Antimicrobial resistance induction potential of grapefruit seed extract on multi-species biofilm of E. coli in food industry.

Biofilm formation in natural environments involving complex multi-structural arrangements hinders challenges in antimicrobial resistance. This study investigated the antimicrobial resistance potential of grapefruit seed extract (GSE) by examining the formation of mono-, dual-, and multi-species biofilms. We also explored the counterintuitive effect in response to GSE at various concentrations, including minimum inhibitory concentration (MIC) and sub-MIC (1/2 and 1/4 MIC). The results of the swimming and swarming motility tests revealed increased motility at the sub-MIC of GSE. The crystal violet assay demonstrated increased biofilm formation in multi-species biofilms, highlighting the synergistic effect of Escherichia coli, Salmonella Typhimurium, and Listeria monocytogenes. At the MIC concentration of GSE, field emission scanning electron microscopy (FE-SEM) revealed cell morphology damage, while sub-MIC increased biofilm formation and architectural complexity. Multi-species biofilms demonstrated greater biofilm-forming ability and antimicrobial resistance than mono-species biofilms, indicating synergistic interactions and enhanced resilience. These findings highlight the importance of understanding biofilm dynamics and antimicrobial resistance to ensure environmental safety.