The effect of new quaternary bisammonium salts (QBAS) of series A: 1,10-[bis(alkyldimethyl-diammonium)]-4,7-dioxo-3,8-dioxounde- candibromides and series B: a-w [bis(dodecyldimethyl-diammonium)]-3,x-dioxo-4,y-dioxoalcandibromides on the growth and surface hydrophobicity of E. cloacae strain was studied. The compounds of series A possess changing side substituent and the inhibition of growth displayed evident dependence of effect on length of alkyl with optimum at C9 – C11 (cut off effect). In series B are compounds with changing joining chain between two ammonium cations where the mentioned effect was not observed. The cell surface hydrophobicity of tested strain was determined by the method of adhesion to hydrocarbon – xylene (BATH) and in salt aggregation test of ammonium sulphate (SAT). The effect of 1/4 of the MIC compounds series A with nonyl, decyl and undecyl reduced the adhesion of E. cloacae cells below 50% against the control. These compounds at sub-MICs decreased salt-aggregative ability of E. cloacae cells. The influencing of cell surface hydrophobicity was not found after affecting of compounds at sub-MIC from series B with the exception of moderate decrease at compound with joining chain of C7. The length of chain connecting two symmetrical parts of molecule has slight impact on the effect of bisammonium salts. The influence of QBAS at sub-MICs on cell surface hydrophobicity can interfere with pathogenic potential of E. cloacae.

        Key words: quaternary bisammonium compounds, cell-surface hydrophobicity, Enterobacter cloacae