(121l) Antibacterial Activity of Cationic Conjugated Oligo/Polyelectrolytes Against Wild Type and Antibiotic-Resistant Bacteria

Overuse and misuse of the antibiotics has caused the emergence of antibiotic resistant bacteria. Antibiotic resistance is a serious health concern for animal and human race. Antibiotic resistant bacteria show resistance to drugs via many mechanisms, one of which is altering the cell envelope. Light harvesting π-conjugated molecules are demonstrated for their killing and/or inhibitory effects mostly on wild-type bacterial strains, but a better understanding of how the conjugated molecules impact the cell envelope of bacteria is critically needed. For the current study, we synthesized phenylene based cationic conjugated oligomers (CCOEs) and polymer (CCPE). The chain length and density of cationic groups at the pendants are varied systematically to probe the interaction of the conjugated oligo/polyelectrolytes with wild-type and ampicillin-resistant E.coli, a gram negative bacteria. One of the interesting findings from this work is that our conjugated molecules are capable of killing or inhibiting the growth of both wild type and antibiotic resistant E. coli, as evidenced from reduction of colony forming units (CFU) and UV-Vis absorbance data. Zeta potential data clearly indicated that the presence of cationic charge in the side chain of CCOEs and CCPEs lead to electrostatic interactions with negatively charges on the outer membrane of gram-negative E. coli. Moreover, we studied mechanical properties (using Bio-AFM), morphological changes (using scanning electron microscope (SEM)) and ionic conductivity (using electrochemical impedance spectroscopy (EIS)) of the wild type and antibiotic resistant bacteria before and after treatment with conjugated molecules. This thorough investigation offered great insight into the binding as well as bacteria killing/inhibiting mechanism of cationic conjugated molecules from the viewpoint of fundamental changes of bacterial outer membrane. The understandings can greatly benefit and guide the future design of antibiotic drugs to fight against antibiotic resistance, coating for medical devices and food packaging materials to ensure food safety.