Studies on the preparation and antibacterial properties of quaternized polyethyleneimine

Quaternized polyethyleneimine (QPEI) was prepared via two types of macromolecular reactions, tertiary amination reaction and quaterization, and its chemical structure was characterized using infrared and UV spectroscopy. In this paper, the antibacterial properties of QPEI were mainly investigated by using Escherichia coli as model bacterium and with the colony count method. The effects of the cationic degree and pH value of the medium on the antibacterial properties of QPEI were examined. The antibacterial mechanism of QPEI was also explored using enzyme activity measurement methods, in which the enzyme activity of two enzymes, beta-D-galactosidase and TTC-dehydrogenase, were measured. The experiments show that QPEI possesses outstanding antibacterial activity because of combination effect of the antibacterial groups on the macromolecular chains. The antibacterial ratio reached 100% for bacterium suspensions of 10(9) CFU/ml with a polymer concentration of 15 mg/l for a contact time of 4 min. The cationic degree influences the antibacterial ability of QPEI greatly, and the higher the cationic degree, the stronger the antibacterial activity. The experimental data indicated that the pI of the E. coli protein is probably 4.5. When pH > 4.5, the antibacterial activity of QPEI increases with increasing pH, and when pH > 6 the antibacterial ratio reaches a maximum and remain nearly constant. The enzyme activity measurement results reveal that the antibacterial action of QPEI is based on a sterilization process. Similar to the small molecular quaternary ammonium salt, QPEI causes cell death by disrupting cell membranes and releasing the intracellular contents.