Ciprofloxacin and the fluoroquinolones. New concepts on the mechanism of action and resistance

DNA gyrase gyrA mutations in ciprofloxacin-resistant strains of Staphylococcus aureus: close similarity with quinolone resistance mutations in Escherichia coli

The gyrA genes isolated from three ciprofloxacin-resistant clinical isolates of Staphylococcus aureus carried codon 84 (serine----leucine) and/or codon 85 (serine----proline) mutations that were absent in pretreatment susceptible strains. These substitutions occur in a region of the gyrase A protein wherein directly analogous mutations of serine 83----leucine and alanine 84----proline in Escherichia coli confer quinolone resistance. Thus, DNA gyrase A subunit mutations are implicated in resistance to ciprofloxacin in S. aureus.

DNA cloning and organization of the Staphylococcus aureus gyrA and gyrB genes: close homology among gyrase proteins and implications for 4-quinolone action and resistance

Staphylococcus aureus gyrA and gyrB genes, which encode the DNA gyrase A and B proteins, have been isolated and found to map contiguously. DNA sequence analysis revealed close homology between the S. aureus gyrase subunits and their counterparts in Bacillus subtilis and Escherichia coli, including several conserved amino acid residues whose substitution in E. coli confers resistance to 4-quinolones. These results are discussed in regard to quinolone resistance mechanisms in S. aureus.

Isolation of fluoroquinolone-resistant Escherichia coli and Klebsiella pneumoniae from an infected Hickman catheter

Escherichia coli and Klebsiella pneumoniae resistant to fluoroquinolones were isolated from an infected Hickman catheter in a 43-year-old diabetic patient who had previously been treated with a 24-day course of ciprofloxacin (200 mg/12 h i.v.). MICs and MBCs of nalidixic acid, norfloxacin, ciprofloxacin, ofloxacin, pefloxacin and fleroxacin were determined for the strains using the methodology recommended by the NCCLS. Both strains were resistant to all the quinolones tested. Since long-term treatment with quinolones might favour the emergence of quinolone resistance or colonization with quinolone-resistant organisms, it is important to monitor for the development of bacterial resistance during therapy with the new fluoroquinolones.