Signature gene expression profile of triclosan-resistant Escherichia coli

To gain further insight into the defence mechanisms against triclosan in a mutant derived from an Escherichia coli strain carrying the triclosan-resistant target enzyme, FabI(G93V). An E. coli imp4231 FabI(G93V) strain was constructed by replacing intact fabI with a linear DNA cassette, fabI(G93V)-Cm(R), that contains a single mutation, GGT to GTT, at codon 93 of fabI(G93V) and a chloramphenicol resistance gene (Cm(R)) as a marker for the mutant allele by a Red-mediated recombination system. Using this E. coli imp4231 FabI(G93V) strain, nitrosoguanidine (NTG) mutagenesis was performed to generate E. coli IFNs [imp4231 FabI(G93V) treated with NTG] displaying higher MICs of triclosan than its parent strain. The genes overexpressed in E. coli IFN4 were identified by DNA microarray analysis. An E. coli imp4231 FabI(G93V) strain displays similar to 400-fold increased MICs of triclosan (MIC similar to 8 mg/L) compared with the parent strain (MIC similar to 0.02 mg/L). Furthermore, E. coli IFN4 has the highest MIC of triclosan (MIC similar to 80 mg/L). DNA microarray analysis of E. coli IFN4 shows that many genes involved in the biosynthesis of membrane proteins, including transporters, reductases/dehydrogenases and stress response regulators, were highly expressed in the mutant. These results strongly indicate that E. coli IFN cells might protect themselves from triclosan by activating various defence mechanisms, such as (i) changing efflux activities; (ii) capturing the triclosan; and (iii) increasing the expression of important regulators or metabolic enzymes.