###### Abstract  
Treatment of infections caused by _Pseudomonas aeruginosa_ presents a challenge due to its ability to adapt and acquire drug resistance rapidly. Therefore, a key challenge is identifying and investigating new compounds with antibacterial and anti-virulence activity. Tannins, a group of plant polyphenic compounds, can interact with bacterial cells and their virulence factors. The purpose of this study was to assess the antibacterial potential of using 3,6-bis-O-di-O-galloyl-I-2,4-tri-O-galloyl-\(\beta\)-D-glucose (C\({}_{\rm 55}\)H\({}_{40}\)O\({}_{\rm 34}\)) isolated from _Rhus typhina_ against _P. aeruginosa_ ATCC BCAA-1744. The investigation involved viability analyses using the INT assay, fluorescence analyses of the tannins' interaction with the cell membrane and membrane proteins of _P. aeruginosa_, and analysis of changes in the Zeta potential. The results obtained allowed us to conclude that C\({}_{\rm 55}\)H\({}_{40}\)O\({}_{\rm 34}\) exhibits antimicrobial activity by inducing changes in the biophysical properties of _P. aeruginosa_'s cell membrane. The thermodynamic parameters indicated that C\({}_{\rm 55}\)H\({}_{40}\)O\({}_{\rm 34}\) binds to bacterial membrane proteins through hydrophobic interactions. These interactions with proteins may impact their structure and disrupt their functions, such as disturbing or inhibiting the efflux pumps, which are part of _P. aeruginosa_'s resistance mechanisms. Therefore, C\({}_{\rm 55}\)H\({}_{40}\)O\({}_{\rm 34}\) may be a new, natural agent and could potentially be used against _P. aeruginosa_. P. aeruginosa; Rhus typhina L.; tannins; antibacterial activity; order parameter; fluorescence analysis; zeta potential Article  
The Molecular Mechanisms of the Antibacterialential Activity of Sumac (_Rhus typhina_ L.) Tannin Against _Pseudomonas aeruginosa_  
[PERSON], [PERSON]; [PERSON]; C.; E.  
innate immunity. On the other hand, _P. aeruginosa_ can also develop adaptive immunity connected with biofilm formation, quorum sensing, and plasmid transfer of genes responsible for antibiotic resistance [6]. It has been described that _P. aeruginosa_ possesses resistance to such antibiotics as carbapenem, fluoroquinolones, and third-generation cephalosporors [7], as well as amino-glycos and \(\beta\)-lactams [6]. The strong pathogenicity of _P. aeruginosa_ is related to its high resistivity and many virulence factors. One of the most important is LPS (lipopolysaccharides), which influences antibiotic tolerance and biofilm formation [8]. The second one is the secretion system, formed of six types (TISS-T6 SS) and responsible, i.a., for attachment to host cells, swarming motility, and biofilm formation by the type IV pili and flagella [9]. _P. aeruginosa_ produces and secretes many factors, like exopolysaccharides, siderophores, proteases (e.g., alkaline proteases and elastases A and B), and toxins--for example, exolysin, ExoT, ExoU, Exotoxin A, phospholipase C, Lipase A, leuccidin or pyocyanin [9]. Due to _P. aeruginosa_'s pathogenicity, connected to its MDR, developing new types of antibiotics is still strongly necessary. For example, [PERSON] et al. described a new generation of cephalospororin [10]. This method, even though it is essential, has a serious limitation. Developing new antibiotics takes a long time, and bacteria will ultimately develop resistance to new drugs. An alternate method can be searching for and investigating other compounds that demonstrate antibacterial potential and to which bacteria will not develop resistivity. Plant polyphenols are compounds that exhibit strong antibacterial activity. Plants naturally synthesize this large group of different molecules that possess a broad spectrum of antibacterial activity against Gram-positive and Gram-negative strains.