Patent ID: 6949383

Claim:
A method for establishing a mutant of Escherichia coli dnaQ49 strain having tolerance to an antibiotic drug, wherein the tolerance is at least 1,000 times higher than that of wild type Escherichia coli, which comprises: (a) introducing a mutation into the genomic DNA of Escherichia coli dnaQ49 strain by culturing it under a certain temperature; (b) selecting a mutant Escherichia coli dnaQ49 strain tolerant to said drug; and (c) repeating said step (a) and said step (b) to develop increased tolerance of said mutant Escherichia coli dnaQ49 strain to said drug until the tolerance is at least 1,000 times higher than that of wild type Escherichia coli, wherein the repeating of said step (b) a second time and thereafter is carried out under a higher concentration of said drug than used in said step (b) therebefore, and wherein the repeating of said step (a) a second time and thereafter is carried out under the same concentration of said drug as used in said step (b) immediately therebefore.