Characterization of a cationic surfactant-resistant mutant isolated spontaneously from Escherichia coli

Abstract

Aims: In order to investigate the mechanism of bacterial resistance to surfactants, a spontaneous mutant of Escherichia coli, OW66, resistant to a cationic surfactant cetyltrimethylammonium bromide (CTAB), was isolated and its physiological properties analysed. Methods and Results: Strain OW66 grew in M9 medium containing CTAB at 45 μmol l^–1, whereas its parent strain, OW6, did not, even at 15 μmol l^–1. The mutant was also resistant to some other surfactants, antibiotics, heavy metals, organic solvents and oxidants examined. To determine the differences in physiology between strains OW66 and OW6, the compositions of their cell surface structures were analysed. In strain OW66, the relative content of OmpC in particular was higher than that of OmpF, whereas a reverse situation was seen in OW6 strain. The lipopolysaccharide (LPS) profile was different between these strains, and altered LPS in strain OW66 was suggested to be involved in the resistance to CTAB. Conclusions: A CTAB‐resistant E. coli isolate possesses an altered outer membrane. Significance and Impact of the Study: Treatment with a relatively low concentration of CTAB was found to introduce multi‐drug resistance into bacterial cells. This acquired resistance should be taken into account with the frequent use of surfactants in industries and various environments.