Quinolones: mechanisms of resistance Niels Frimodt-Møller National Center of Antimicrobials and Infection Control Statens Serum Institut Copenhagen, Denmark

Quinolone mechanisms of resistance Change in receptor Mutations in genes for gyrases/topoisomerases 2) Change in penetration Efflux-mechanisms: Proton-pumps with active transport of quinolone out of cell 3) Enzymatic degradation Always (almost) chromosomal (plasmid carried transfer found in Klebsiella, mechanism?)

Gram negativ bakterie kinolonresistensmekanismer. DNA + gyrasekomplex Effluxpumper Porer

DNA Structure of the Topo I/DNA complex.  During replication, the unwinding of DNA may cause the formation of tangling structures, such as supercoils or catenanes.  The major role of topoisomerases is to prevent DNA tangling.

The structure of supercoils The structure of supercoils.  (a) Positive supercoils - the front segment of a DNA molecule cross over the back segment from left to right.  (b) Negative supercoils.  (c) The positive supercoil in bacteria during DNA replication.

There are two types of topoisomerases: type I produces transient single-strand breaks in DNA: The topo I of both prokaryotes and eukaryotes and types II produces transient double-strand breaks: The eukaryotic topo II, bacterial gyrase, and bacterial topo IV belong to the type II The gyrase has two functions: (1) to remove the positive supercoils during DNA replication, (2) to introduce negative supercoils (one supercoil for 15-20 turns of the DNA helix) so that the DNA molecule can be packed into the cell.  During replication, these negative supercoils are removed by topo I. Malfunction in topoiomerases causes cell death.  .

The function of topo II: (a) To remove supercoils The function of topo II:   (a) To remove supercoils.  This  involves a double-strand break (indicated by a short line), allowing the tangled segment to pass through.  The break is then resealed.  (b) To remove catenanes.  The topo II makes a double-strand break in one DNA molecule (the blue one), allowing the other molecule to pass through.  The break is then resealed.

Quinolone resistance mechanism

Quinolone resistance mechanism Mutations in gyrA QRDR resistance in Gram-negatives Mutations in parC QRDR resistance in Gram-positives

Gram negativ bakterie kinolonresistensmekanismer. DNA + gyrasekomplex Effluxpumper Porer

Accumulation of moxifloxacin in P Accumulation of moxifloxacin in P. aeruginosa +/- CCCP (efflux inhibitor) Ng mox./mg dry cell Minutes

Accumulation of ciprofloxacin and lomefloxacin in fluoroquinolone-resistant strains of Escherichia coli XIA Peiyuan et al. Chin Med J 2002; 115:31-5. Accumulation of LMLX in E. coli strains. Each curve indicates the accumulated concentration of LMLX in one strain at diffe rent time point.JF701 and JF703: control strains; Ecs: susceptible strain. R 2 and R256: the in vitro selected resistant strains; R5 and R6: the clinical res istant strains.

Involvement of Topoisomerase IV and Gyrase as Ciprofloxacin targets in S. pneumoniae Strain Mutations in QRDR of: ParC GyrA GyrB ParE Cipro MIC D5 1 B10 Ser-79 Phe 4 D11 Glu-87 > Lys 64 E4 Arg-95 Cys Pan et al. Antimicrob Ag Chemother 1996, 40: 2321-6

Quinolone resistance types in E. coli Strain Mutation in gyrA Mutation in parC Redu- ced accum. Cipro MIC Moxiflox ATCC25922 0.008 0.03 WT-4 S80I 0.25 MI S83 0.5 1 WT-3 S83+D87 2 WT-3-M4 64 32 MII + 4 MIII 256 128 Schedletzky et al. JAC, 1999, 43 suppl.B: 31-7

Effect of fluoroquinolone concentration on the recovery of single-step, resistant mutants. Moxifloxacin (open circles) or levofloxacin (solid circles). Unlabeled arrows indicate MIC99. The triangle indicates no colony recove-red at that drug concentration and bac-terial load. The dashed line indicates one colony recovered per 1010 cells tested. Three strains were tested: wild-type strain ATCC 49619 (A); strain KD2138, a ParC (Ser-79 to Tyr) variant (B); and strain KD2139, a GyrA (Ser-81 to Phe) variant (C). Two double mutants were recovered from each point indicated by an arrow. Li et al. Antimicrob Ag Chemother 2002, 46: 522-524.

Changes in the susceptibility of S Changes in the susceptibility of S. aureus 201 during and after 3-day treatments with four fluoroquinolones at different AUC24/MIC ratios. Firsov et al. Antimicrob Ag Chemother 2003, 47: 1604-1613

Relationship of pharmacokinetics and MPC Mutant Prevention Concentrations of Fluoroquinolones for Clinical Isolates of Streptococcus pneumoniae Blondeau et al., Antimicrob Ag Chemother 2001, 45: 433-438 Relationship of pharmacokinetics and MPC Fluoroquinolone MPCpr90 (µg/ml) Dose (mg) Cmax (µg/ml) t1/2 (h) Moxifloxacin 2 400 4.5 12 Gatifloxacin 4 4.2 8 Trovafloxacin 200 3.1 Grepafloxacin 600 <2.7 14 Levofloxacin 500 5.7

Combination therapy resulted in lower rates of resistance. Thomas JK, et al. Antimicrob Agents Chemother 1998; 42: 521-7. Pharmacodynamic evaluation of factors associated with the development of bacterial resistance in acutely ill patients during therapy. Five different regimes in ICU could be avaluated for resistance developments in different bacterial species (total of 128 patogenes in 107 ptt.). cirofloxacin alone ciprofloxacin + piperacillin ceftazidime alone ceftazidime +tobramycin cefmenoxime alone The overall predictor for development of resistance was AUC/MIC < 100. Combination therapy resulted in lower rates of resistance.

Thomas JK et al. Antimicrob Ag Chemother 1998; 42: 521-7. Resistance developed in -lactamase-type-I Gram-neg. rods even when AUC/MIC > 100 after -lactam monotherapy. Median time to resistance: 6 days if AUC/MIC < 100. AUC/MIC > 100 AUC/MIC < 100

Quinolone resistance: Summary Mutations in genes for topoisomerases (gyr, par): MIC increases with no. of mutations; rate ~ 1 in 10-7 Changes in efflux mechanisms: Pumps out drug; NB: inhibitors; Can be first step in development of resistance Both 1 and 2 can be present in same strain – leads to high MIC´s Majority of R-genes chromosomal – plasmid transported gene reported