Cross-resistance to antibiotics of Escherichia coli adapted to benzalkonium chloride or exposed to stress-inducers

Aims: To study the effects of adaptation and stress on the resistance to benzalkonium chloride (BC) and cross-resistance to antibiotics in Escherichia coli. Methods and Results: Precultivation of E. coli ATCC 11775 and E. coli DSM 682 in the presence of subinhibitory concentrations of BC or stress inducers (salicylate, chenodeoxycholate and methyl viologen) resulted in higher minimum inhibitory concentration (MIC) of BC and chloramphenicol (CHL). Adaptation to growth in sixfold of the initial MIC of BC resulted in stable BC resistance and enhanced tolerance to several antibiotics and ethidium bromide (EtBr). The MIC of CHL increased more than 10-fold for both strains. Enhanced efflux of EtBr in adapted E. coli ATCC 11775 indicated that the observed resistance was due to efflux. Changes in outer membrane protein profiles were detected in the BC-adapted cells. There were no indications of lower membrane permeability to BC. Conclusions: Induction of stress response or gradual adaptation to BC or CHL results in acquired cross-tolerance between BC and antibiotics in E. coli. Enhanced efflux was one of the observed differences in adapted cells. Significance and Impact of the Study: Provided not taking due precautions, extensive use of disinfectants could lead to emergence of antibiotic-resistant isolates.