Adapted tolerance to Benzalkonium chloride in E. coli K12

Benzalkonium chloride (BC) is a commonly used disinfectant and preservative. This study describes changes in expression level on the transcriptomic and proteomic level for Escherichia coli K12 gradually adapted to a tolerance level towards BC of 7-8 times the initial MIC. Results from DNA arrays and two-dimensional (2-DE) gel electrophoresis for global gene and protein expression studies were confirmed by real time quantitative PCR. Peptide mass fingerprinting by MALDI-TOF MS was used to identify differentially expressed proteins. Changes in expression level in adapted cells were shown for porins, drug transporters, glycolytic enzymes, ribosomal subunits and several genes and proteins involved in protection against oxidative stress and antibiotics. Adapted strains showed increased tolerance to several antibiotics. In conclusion, E. coli K12 adapted to higher tolerance to BC, acquired several general resistance mechanisms including responses normally related to the multiple antibiotic resistance (Mar) regulon and protection against oxidative stress. The results revealed that BC treatment might result in superoxide stress in E. coli. Keywords: Study of resistance mechanism E. coli K12 was adapted to grow in the presence of benzalkonium chloride in three independen experiments resulting in three adapted strains (BCadapted1, BCadapted2 and BCadapted3). Control strains were cultivated in TSB before harvesting and adapted strains were cultivated either in TSB with or without 50 ppm benzalkonium chloride before harvesting. Cultures for transcriptional analysis were harvested three times at different days resulting in three replicate experiments. Samples from the fist day is termed replicate1, day 2 is termed replicate2 and day three replicate3. For the controls, samples from two cultures were sampled for replicate one and two.