Correlation between the bacterioclastic action of a bis-quaternary ammonium compound and outer membrane proteins

Bis-quaternary ammonium compounds (bis-QACs) have the ability to cause a rapid and abundant leakage of the turbid materials from cells, and such a bacterioclastic ability leads to a potent bactericidal activity. In order to clarify the detailed mechanism of the bactericidal action of bis-QACs, the correlation between the bacterioclastic action of 4,4'-(1,6-hexamethylenedithio)bis(1-octylpyridinium bromide) (4DTBP-6,8) and the leakage of outer membrane pore protein E (OmpE) was investigated. Using the antiserum against a fusion protein consisting of GST and the OmpE protein of Escherichia coli encoded by the ompE gene, it was seen that the leakage of OmpE from E. coli cells was caused by treatment with low concentrations (much lower than the critical vesiculation concentration) of 4DTBP-6,8. Furthermore, it was confirmed that 4DTBP-6,8 caused an increase in the turbidity of the cell suspension of Klebsiella pneumoniae, Salmonella typhimurium and Serratia marcescences, and led to the leakage of several proteins which have a high percentage of homology with OmpE of E. coll. By immunoelectron microscopy investigation, it was revealed that the vesiculation from E. coli treated with 4DTBP-6,8 contains OmpE. In addition, the bacteriolytic action of 4DTBP-6,8 was investigated. The results suggested that the lysis of cells by bis-QACs was not an enzymatic action such as that by autolysin but a physical bacterioclastic action. Judging from these results, it is suggested that the leakage of OmpE is one of the major bacterioclastic actions of bis-QACs, and deals the bacterial cells a fatal blow.