Norfloxacin induced resistance to fluoroquinolones & structurally unrelated antimicrobial agents in coagulase negative staphylococci.

Nine clinical isolates of coagulase negative staphylococci (CONS) susceptible to norfloxacin (MIC 1.8-2 micrograms/ml) were manipulated in vitro to induce norfloxacin resistance by means of serial passage in brain heart infusion broth containing increasing concentrations of norfloxacin. Exposure of CONS to norfloxacin resulted in 18 to 20 times increase in MIC of norfloxacin and change in in vitro susceptibility to ciprofloxacin, pefloxacin, ofloxacin, kanamycin, neomycin and tobramycin, indicating development of cross resistance to fluoroquinolones and aminoglycosides. These results show that exposure to increasing concentrations of norfloxacin can induce the development of resistance to various antimicrobial agents, suggesting its mutagenic role.