5,6-dihydroxyflavone

Baicalin, a bioactive flavone found in Scutellaria baicalensis Georgi has anti-SARS-CoV-2 infection by targeting viral 3C-like protease (3CLpro). However, little is known about the antiviral activity of its 7-deoxy analogue, 5,6-dihydroxyflavone (5,6-DHF), especially against betacoronaviruses (beta-CoVs). We found that 5,6-DHF exhibited more potent anti-SARS-CoV-2 Omicron variant EG.5.1.1 activity than baicalein by microneutralization test (MNT) and plaque reduction neutralization test (PRNT). 5,6-Dihydroxyl (catechol) groups at A ring of 5,6-DHF is essential for its suppression on SARS-CoV-2 Omicron variant EG.5.1.1 infection because blocking them with methyl or methylene groups obsolesce the activity. 3CLpro inhibition assay showed that the antiviral activity of 5,6-DHF is distinctive with baicalein. Time of addition test, molecular docking and spike-bearing pseudotyped virus entry assay suggested that 5,6-DHF interferes the spike-ACE2 interaction by targeting at receptor binding domain (RBD) of spike and hence inhibits the virus replication. In addition to SARS-CoV-2 Omicron variant EG.5.1.1, 5,6-DHF was also found effective against another common human beta-CoVs, HCoV-OC43, by blocking their entry to host cells. Taken together, the present study demonstrated the potential function of 5,6-DHF as a therapeutic candidate against beta-CoVs.

In this study, Salmonella Typhimurium dry surface biofilm (DSB) formation was investigated in comparison with wet surface biofilm (WSB) development. Confocal laser scanning microscopic analysis revealed a prominent green cell signal during WSB formation, whereas a red signal predominated during DSB formation. Electron microscopy was also used to compare the features of DSB and WSB. Overall, WSB was unevenly scattered over the surface, whereas DSB was evenly dispersed. In contrast to WSB cells, which have a distinct plasma membrane and outer membrane layer, DSB cells are contained in large capsules and compressed. Next, microbiome single-cell transcriptomics was used to investigate the functional heterogeneity of the Salmonella DSB microbiome, with nine clusters successfully identified. Although over 60% of the dried cells were metabolically inactive, the rest of the Salmonella cells still demonstrated specific antioxidative and virulence capabilities, suggesting a possible concern for low-moisture food (LMF) safety. Finally, because sanitization in LMF industries must be conducted without water, a list of 39 flavonoids was tested for their combined effect with 70% isopropyl alcohol (IPA) against DSB, and morin induced the greatest reduction in the green:red ratio from 3.67 to 0.43. Significantly higher reductions of Salmonella viability in DSB were achieved by 10-, 100-, 1,000-, and 10,000-µg/mL morin (1.69 ± 0.25, 3.21 ± 0.23, 4.32 ± 0.24, and 5.18 ± 0.16 log CFU/sample reductions) than 70% IPA alone (1.55 ± 0.20 log CFU/sample reduction) ( P < 0.05), indicating the potential to be formulated as a dry sanitizer for the LMF industry.

DSB growth of foodborne pathogens in LMF processing environments is associated with food safety, financial loss, and compromised consumer trust. This work is the first comprehensive examination of the characteristics of Salmonella DSB while exploring its underlying survival mechanisms. Furthermore, morin dissolved in 70% IPA was proposed as an efficient dry sanitizer against DSB to provide insights into biofilm control during LMF processing.