Insight into the\nAntibacterial Activities of Pyridinium-Based\nCationic Pillar[5]arene with Controllable Hydrophobic Chain Lengths\nagainst Staphylococcus aureus

The increasing number of infections\ncaused by pathogenic\nbacteria\nhas severely affected human society. More and more deaths were originated\nfrom Gram-positive methicillin-resistant Staphylococcus\naureus (MRSA) infection each year. The potential and\nexcellent bacteriostatic activity and resistance to biofilm formation\nof pillar[5]arene with different functional groups attract important\nattention to further study the relationship between antimicrobial\nactivity and cytotoxicity by varying the length of the hydrophobic\nchain, the number of positive charges, and the hydrophobic/hydrophilic\nbalance of the molecule. In this work, four pyridinium-based cationic\npillar[5]arene (<b>PP</b>s) with linear aliphatic chains of\ndifferent lengths were synthesized. After systematic characterization,\ntheir inhibition activities against S. aureus were investigated. It revealed that <b>PP6</b> (six methylenes\nin each linker) exhibited excellent inhibition activity against S. aureus (ATCC 6538) with a minimum inhibitory concentration\n(MIC) of 3.91 μg/mL and a minimum bactericidal concentration\n(MBC) of 62.50 μg/mL. As expected, <b>PP6</b> exhibited\nthe strongest antibiofilm ability and negligible antimicrobial resistance\neven after the 20th passage. A study of the action mechanism of selected <b>PP</b>s on the bacterial membrane depolarization and permeability\nby transmission electron microscopy (TEM) disclosed that the cationic\npyridine groups of <b>PP</b>s inserted into the negatively charged\nbacterial membranes, thereby leading to membranolysis, cytoplasmic\ncontent leakage, and cell death. Importantly, <b>PP</b>s all\nshowed very low toxicity to mammalian cells (L929 and HBZY-1), which\nprovided a significant reference for the construction of hypotoxic\nantibacterial biomaterials for multiple drug-resistant bacteria based\non pyridinium-grafted cationic macrocycles with controllable hydrophobic\nchain lengths.