Kojic acid and tea polyphenols inactivate Escherichia coli O157:H7 in vitro and on salmon fillets by inflicting damage on cell membrane and binding to genomic DNA

Abstract

Summary The development of effective natural antibacterial agents is important due to the insecurity of synthetic antimicrobial agents and consumer preferences. In this study, kojic acid (KA) and tea polyphenols (TP) were found to exhibit synergistic inhibitory effect against Escherichia coli O157:H7 with a fractional inhibitory concentration index of 0.25. KA combined with TP at 25% of their minimum inhibitory concentrations (MICs) completely inactivated E. coli O157:H7 within 4 h. Subsequently, propidium iodide uptake tests, genomic DNA interaction analysis, molecular docking, field emission scanning electron microscopy and biofilm formation assay were conducted to understand the synergistic antibacterial mechanism of KA‐TP. The results demonstrated that KA‐TP attacked the cell membrane cooperatively, thus disturbing membrane integrity and cell structure, and KA could bind to the genomic DNA to affect the biofilm formation of E. coli O157:H7. Moreover, the contamination of E. coli O157:H7 on raw salmon fillets was eliminated to varying degrees after soaking treatments with KA and/or TP for 30 min. The depuration effect was further enhanced when KA combined with TP, and more than 2‐log reduction of E. coli O157:H7 was obtained under the treatment of KA‐TP at 2 MIC, suggesting that KA‐TP may serve as a natural compound disinfectant for ready‐to‐eat aquatic products.

Antibacterial mechanism of kojic acid and tea polyphenols against Escherichia coli O157:H7 through transcriptomic analysis

“…YhbQ is a metal-dependent endonuclease (Mg 2+ , Mn 2+ and Co 2+ ) with high activity against nucleotide excision repair and DNA recombination intermediates [43]. Consistently, our former research showed that KA is bound with DNA similarly to ethidium bromide in vitro, which might interfere with DNA replication, transcription and other processes [18]. In conclusion, these phenomena suggested that KA could inactivate E. coli O157:H7 by causing acid stress and oxygen starvation and destroying cell membranes and genomic DNA, and DNA seemed to be the most important target to the relatively higher up-regulation of related genes.…”

“…Previous studies confirmed that KA contributes to membrane damage by scanning electron microscope [18]. Previous studies about the antibacterial mechanisms stated that cell membranes and genomic DNA might be the critical targets of KA and its derivatives [8,39].…”

“…According to the previously determined sublethal concentrations of KA and TP against E. coli O157:H7, four sets of samples were selected for transcriptomic analyses to explore the antibacterial mechanisms of KA, TP, and their combination [18]. The bacterial suspensions were treated with: 1) CK: sterile TSB without antibacterial substances; 2) T1: sterile TSB with 1/2 MIC KA; 3) T2: sterile TSB with 1/2 MIC TP and 4) T3: sterile TSB with 1/5 MIC KA + 1/5 MIC TP, and then incubated at 37 ℃ for 8 h.…”

“…The KA and TP against E. coli O157:H7 have caused varying degrees of cell membrane integrity destruction, genomic DNA degradation and affected biofilm formation [18]. Some studies have expounded the antibacterial mechanism of TP or its main components (epigallocatechin gallate, etc.)…”

“…Besides, our previous study has stated that a combination of kojic acid and tea polyphenols exhibited better against E. coli O157:H7 than using either alone. KA and TP exhibited synergistic inhibitory effects on gram-negative pathogens and spoilage bacteria based on their different subcellular targets and mechanisms, showing a good application prospect in aquatic products [18]. Therefore, a deeper understanding of about the antibacterial mechanisms and molecular targets of KA combined with TP on bacteria is required for their practical applications as disinfectants or preservatives in the food industry.…”