Antibiotic Resistance of Multiple-Antibiotic-Resistance (Mar) Mutants of Escherichia coli K-12

ABSTRACT

Multiple-antibiotic-resistance (Mar) mutants were prepared from the wild-type Escherichia coli K-12 MC4100 or W3110, were analyzed for the antibiotic resistance by minimal inhibitory concentration (MIC), and compared with their isogenic parent strains and E. coli clinical isolates. Mutation frequency was approximately 10-7 to 10-9 MIC levels of chloramphenicol (Cm), ampicillin (Ap), tetracycline (Tc), or ciprofloxacin (Cp) antibiotics against E. coli Mar mutants were 50 ug/ml, 300 ug/ml, 200 ug/ml, or 30 ug/ml, respectively, at their highest MIC levels. Cross-resistances of each Mar mutants against Cm, Ap, Tc, Cp, erythromycin (Em), nalidixic acid (Na), and rifampin (Rf) were evaluated. Almost all of Mar mutants showed approximately 9 to 140-fold increase of MIC with contrast to the MIC of isogenic parent strains and E. coli clinical isolates, except Rf antibiotics. The induction multiplicity of Mar mutants by salicylate (SAL) was approximately the same, 2 to 10-fold, and 2 to 25-fold increase of MIC, in case of E. coli clinical isolates, Mar mutants derived from MC4100, and W3110, respectively.