Plasmid-Mediated Quinolone Resistance

Abstract

In the 1990s quinolone resistance increased in parallel with increased quinolone utilization (1) and also with the emergence of plasmid-mediated quinolone resistance. The fi rst type of plasmid-mediated resistance was discovered in a clinical strain of Klebsiella pneumoniae isolated at the University of Alabama in 1994 that transferred low-level quinolone resistance along with resistance to several other antibiotics to Escherichia coli and other Gram-negative organisms (2). In E. coli the plasmid caused an eight- to 32-fold decrease in susceptibility for nalidixic acid and for all fl uoroquinolones tested. Although the increased minimum inhibitory concentration (MIC) may remain in the susceptible range as defi ned by the CLSI, the presence of the plasmid raised the mutant protective concentration (3, 4) and facilitated the selection of truly quinolone-resistant mutants (2).