Research on potential antibacterial Chinese herbal medicine screening based on Pseudomonas aeruginosa quorum sensing system
Pseudomonas aeruginosa (PA) is associated with various infections. Recent studies have found that resistance to PA is enhanced through quorum sensing during antibiotic treatment. In recent years, due to the widespread use of antibiotics, PA has developed resistance to multiple antibiotics, making the treatment of clinical PA infections significantly more difficult. Seeking new drugs to suppress drug-resistant PA has become an urgent global issue. Given the abundant resources of traditional Chinese medicine in our region, this project considers starting from traditional Chinese medicine and targeting key proteins involved in quorum sensing. Using molecular docking method, search for ligand molecules with high affinity for active sites in the traditional Chinese medicine compound library. By using antibacterial tests to validate the results of virtual screening, we aim to identify Chinese herbal medicines that can inhibit PA resistance in clinical practice, in combination with antibiotics.
Quorum sensing (QS) is an intercellular communication system that coordinates the expression of virulence in bacterial populations. The mechanism consists of five points: (1) overexpression of efflux pump genes; (2) Inactivating enzymes hydrolyze drugs; (3) Biofilm formation; (4) Target mutation; (5) Decreased outer membrane permeability.
The quorum sensing system of PA includes at least four subsystems: Pseudomonas quinolone signal (PQS), integrated quorum sensing signal (IQS), and LAS and RHL systems. Therefore, compared with traditional antibiotics, quorum sensing inhibitors (QSIs) can reduce the toxicity of PA, decrease drug resistance, avoid sepsis, and improve the sensitivity of antibiotic treatment.

The problem of PA resistance is becoming increasingly serious, which poses significant challenges to the therapeutic efficacy of antibiotics in clinical practice. The QS system is widely present in various bacteria, especially PA, and exhibits cascade regulation between systems, regulating the pathogenicity and drug resistance of bacteria. Compared with traditional antibiotics, QSIs can inhibit the QS system of target bacteria at appropriate concentrations without affecting normal bacterial growth, reducing bacterial virulence and inhibiting the spread of bacterial toxins. The five proteins used in this article correspond to different pathway proteins. Among them, 5EOE is a BEL-1 type protein that can produce inactivating enzymes to break down the β – lactam ring, leading to the inactivation of this type of antibiotic; 4HEF is a cephalosporin hydrolase complex belonging to the quorum sensing LAS subsystem. It inhibits serine β – lactase by forming a covalent binding enzyme complex similar to β – lactase, providing a structural basis for its broad-spectrum inhibitory performance; 4ZZL is a mutant of MexR-R21W, which is an inhibitor of the MexAB OprM multidrug efflux pump operator in Pseudomonas aeruginosa. The DNA binding damage mutation leads to multidrug resistance. 4NR0 is an enoyl ACP reductase produced for PA, which plays an important role in the synthesis of virulence factor 3-oxo-C12HSL. 3H78 is a complex composed of a signal biosynthetic enzyme mutant of quinolone pseudomonas and ortho aminobenzoate, which is an important catalyst for biosynthesis in the bacterium. Inhibiting this complex can reduce the production of virulence factors in the PQS system and decrease drug resistance.
In recent years, studies have shown that some commonly used clinical drugs also have QSIs activity. Aspirin, as a traditional antipyretic and analgesic drug, has been found to not affect the growth of PA at a concentration of 6mg/mL, while also exerting a certain inhibitory effect on QS virulence factors such as elastase and pyocyanin. The insecticide chloramphenicol can inhibit the production of PA virulence factors and the formation of biofilms. In addition, some artificially synthesized drugs also possess the properties of QSIs. For example, a synthetic derivative based on furanone (5Z) -4-bromo-5- (bromomethylene) -3-butyl-2- (5H) – furanone), furanone C-30, can inhibit the expression of efflux pumps and virulence factors, increasing the sensitivity of PA biofilm to antibiotics. But so far, almost all of these studies have remained in the laboratory field, and their clinical activity still needs further research.
This article uses MOE software to virtually screen the active ingredients of 2733 common Chinese herbal medicines, and obtains 7 Chinese herbal medicines that may have inhibitory effects on drug-resistant strains: gallnut, ramie root, sheep hoof nail, fire charcoal mother, leaf pearl, water pine, and multi flowered wild peony. Subsequently, relevant antibacterial validation was conducted on it, and the results were consistent with the molecular docking calculations, indicating that this screening has a certain degree of rationality. The computer virtual screening method used in this study has the characteristics of low cost and high efficiency. Combining calculations in traditional pharmacological experiments can lead to more efficient research. However, it is worth mentioning that some traditional Chinese medicines have not been obtained in virtual computing, but have shown antibacterial activity in actual screening (such as Yanfumu, Xiqingguo, Hezi, etc.), indicating that this method is still relatively crude, with deviations and omissions, and needs to be improved. In the later stage, molecular dynamics simulation will be used to analyze important scientific issues such as the system’s mobility and inhibition mechanism.
Regarding the selected Chinese herbs in this article, Chen et al. observed that under certain circumstances, gallnuts have a certain clearing effect on PA biofilm, even completely clearing it; Song et al. found that the extract of Chinese medicinal herb Charcoal has a certain inhibitory effect on the growth of PA, and its minimum inhibitory concentration is 15.63mg/mL; Pandey et al. found through in vitro antibacterial experiments that extracts of sheep hoof beetle (leaves, stem bark, and flowers) have a certain antibacterial effect on PA.
Another purpose of this article is to provide clinical responses to antibiotic resistant PA infections. We are currently collaborating with clinical departments to select various traditional Chinese medicines, which will be decocted and combined with amoxicillin, cefotaxime, and levofloxacin to observe their therapeutic effects and make some progress. However, clinical Chinese medicine practitioners have provided feedback that stronger traditional Chinese medicine formulas are needed in order to achieve better prognosis. Although most compounds are still in the stage of biological activity research or preclinical research, and there are relatively few compounds entering the clinical trial stage, there will still be a lot of uncertainty in the future. However, these compounds with different mechanisms of action provide valuable experience and research ideas for researchers, making the emergence of new antibacterial drugs possible. QSIs have good application prospects, and the reported QSIs are still limited. It is necessary to study safe and efficient QSIs that are truly suitable for human use to solve the problem of bacterial resistance in medicine.