NORFLOXACIN INDUCED RESISTANCE TO FLUOROQUINOLONES AND STRUCTURALLY UNRELATED ANTIMICROBIAL AGENTS IN COAGULASE-NEGATIVE STAPHYLOCOCCI

Nine clinical isolates of coagulase negative staphylococci(CONS) susce ptible to norfloxacin (MIC 1.8-2 mu g/ml) were manipulated in vitro to induce norfloxacin resistance by means; of serial passage in brain he art 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 ciprofl oxacin pefloxacin, ofloxacin, kanamycin, neomycin and tobramycin, indi cating development of cross resistance to fluoroquinolones and aminogl ycosides. These results show that exposure to increasing concentration s of norfloxacin can induce the development of resistance to various a ntimicrobial agents, suggesting its mutagenic role.