Phenotypic changes in ciprofloxacin-resistant Staphylococcus aureus

The work described here continues our studies of the effects of subinhibitory concentrations of antibiotics on SOS and DNA repair gene expression in Staphylococcus aureus. Mitomycin C and the new-generation fluoroquinolone moxifloxacin induced expression of SOS response genes (lexA, recA, sosA, and umuC) in a ciprofloxacin-resistant Cip(r)I strain of S. aureus. To examine phenotypic changes in Cip(r) strains mutated in CIP targets (GrIA and/or GyrA), we used Biolog Phenotype MicroArrays (TM). Two other Cip(r) strains mutated in the nor promoter region were used to study the effects of subinhibitory concentrations of DNA-damaging antibiotics on norA expression. We show that mitomycin C and moxifloxacin induced overexpression of the norA gene in Cip(r) strains. Finally, we confirm that subinhibitory concentrations of CIP increase mutation rates in S. aureus. (C) 2009 Elsevier Masson SAS. All rights reserved.