Synergistic antimicrobial effect and mechanism of enterocin Gr17 and cinnamaldehyde against Escherichia coli and Candida albicans.

Abstract

Bacteriocins and essential oils have potential synergistic antimicrobial effects against pathogens, but the poor understanding of their antimicrobial mechanisms, especially against Gram-negative bacteria and fungi, restricts their practical use in public health. Enterocin Gr17 (ENT) is a novel class IIa bacteriocin that exhibits synergistic effects with cinnamaldehyde essential oil (CEO) against some pathogenic Gram-negative bacteria and fungi. This study aimed to further understand the synergistic antimicrobial activity and mechanisms of ENT and CEO against pathogenic Escherichia coli and Candida albicans from the perspectives of cell wall and membrane, morphological structure, respiratory metabolism and gene expression. Results showed that the ENT-CEO combination induced sublethal damage to E. coli and C. albicans, synergistically limiting their growth in a time-dependent manner. For E. coli, ENT and CEO synergistically disrupted the cell wall structure via interfering with membrane potential and targeting cell wall components, then enhanced membrane permeability and formed non-selective pores, leading to K⁺ and adenosine triphosphate efflux and severe damage of morphology and intracellular organization. Furthermore, their combination also suppressed the hexose monophosphate respiratory pathway and the expression of growth and virulence-related genes, ultimately accelerating cell death. On the other hand, ENT combined with CEO minimally affected C. albicans morphology but severely disrupted its intracellular organization, indicating mechanistic differences from E. coli. Initially, ENT and CEO synergistically destabilized membrane potential and destroyed C. albicans cell wall homeostasis, facilitating their cellular internalization. They subsequently disrupted cell membrane permeability and integrity, impaired energy metabolism by inhibiting tricarboxylic acid cycle pathway, and down-regulated the growth and virulence-related gene expression, thereby leading to C. albicans cell death. This study provides theoretical support for the industrial application of bacteriocin-essential oil synergistic antimicrobial technology.