Generation of clones with higher resistance to tetracycline and chloramphenicol from ciprofluoxacin resistant Escherichia coli mutants

ABSTRACT: Resistance to ciprofloxacin is mostly associated with mutations in gyrA or marR or a combination of both in Escherichia coli. Mutation in marR reduces the accumulation of ciprofloxacin due to activation of AcrAB-TolC, a multidrug efflux pump. The activation of this pump causes low resistance to other antibiotics, such as tetracycline and chloramphenicol and even organic solvents, such as hexane and cyclohexane. However, this low resistance can be amplified by stepwise exposure to increasing amounts of tetracycline in both clinical and laboratory isolates of Escherichia coli. The aim of this study was to produce clones with higher resistance to tetracycline and chloramphenicol from Escherichia coli gyrA mutants with or without mutation in marR useing above procedure. Resulted clones had intermediate levels of resistance to tetracycline and chloramphenicol and better growth on hexane in comparison with original mutants. However, they still could not grow on cyclohexane. It is concluded that to produce clones with high levels of resistance to antibiotics the above procedure should be continued with higher amounts of tetracycline.