Resistance to new anti-grampositive agents Roland Leclercq, Microbiology, CHU Cote de Nacre, Caen, France
Recently available antimicrobials against MDR Gram-positive infections Cyclic lipopeptide: daptomycin Oxazolidinone: linezolid Glycylcycline: tigecycline Under development: analogs of vancomycin and teicoplanin (dalbavancin oritavancin, telavancin), new cephalosporins (ceftobiprole), iclaprim
Tigecycline Tigecycline overcomes the 2 major resistance mechanisms of tetracycline: drug-specific efflux pump acquisition and ribosomal protection Wide spectrum, bacteriostatic Tigecycline MICs (mg/l) Range MIC50 MIC90 MSSA (813) 0.015-0.5 0.12 0.25 MRSA (879) 0.03-0.5 0.12 0.25 E. faecalis (740) 0.015-0.5 0.06 0.12 E. faecium (280) 0.015-0.5 0.06 0.12 Waites et al. Antimicrob Agents Chemother. 2006;50:3479-84
In vitro selection of MRSA mutants resistant to tigecycline Selection of MRSA (N315 and Mu3) mutants resistant to tigecycline after serial passages (n=16) (MIC=4 mg/l) Analysis of transcription profiles: 100-fold increased expression of a gene cluster, meprab (multidrug export protein) in mutants meprab encoded a MarR-like transcriptional regulator (mepr), a novel MATE family efflux pump (mepa), and a hypothetical protein of unknown function (mepb). Mutations of mepr gene in the mutants presumably inactivated the MepR repressor McAleese et al., Antimicrob Agents Chemother 2005, 49:1865-71
Efflux pumps in Gram-positive bacteria Piddock Nature Reviews Microbiology 4, 629 636 (August 2006)
Daptomycin Daptomycin has a membrane-based mode of action calcium-dependent membrane depolarization of S. aureus and potassium release from. A model for the bactericidal action of daptomycin involving oligomerization of daptomycin and disruption of the functional integrity of the cytoplasmic membrane has been proposed.
Daptomycin: transcriptional profiling studies Potential dual mode of action of daptomycin involving both cell wall inhibition and membrane depolarization Muthaiyan A, Silverman JA, Jayaswal RK, Wilkinson BJ. Antimicrob Agents Chemother. 2008;52:980-90.
Correlation between reduced daptomycin susceptibility and vancomycin resistance in GISA/VISA Cui, L. Z., E. Tominaga, H. M. Neoh, and K. Hiramatsu. 2006. Antimicrob. Agents Chemother. 50:1079 1082
Resistance to daptomycin in Gram-positive organisms Daptomycin-resistant S. aureus and Enterococcus spp. during prolonged treatment with daptomycin has been reported (Fowler et al., N Engl J Med, 355:653 65; Hayden et al, J. Clin. Microbiol. 43:5285 7; Lewis et al., Antimicrob. Agents Chemother. 49:1664 5. Munoz-Price et al, Clin. Infect. Dis. 41:565 566). Genome comparisons of susceptible and resistant laboratory-derived S. aureus identified mutations in various genes: mprf (a membrane lysylphosphatidylglycerol synthetase), yycg (a histidine kinase), and rpoc and rpob (subunits of RNA polymerase). Friedman, L., J. D. Alder, and J. A. Silverman. 2006. Antimicrob. Agents Chemother. 50:2137 45
Oxazolidinone: linezolid Solubility (morpholine group) Activity Small molecule: MW 337.35 (vancomycin 1500)
Binding of linezolid to 23S rrna (E. coli model) Leach et al. Mol Cell. 2007 11;26:393-402
Resistance to linezolid Unfrequent resistance by mutation of 23S rrna reported in enterococci and staphylococci: essentially G2576 mutation in clinical isolates. Bacteria have several copies of rrna operons. The copy number depends on the species. The level of resistance is proportional to the number of mutated RNA operon copies.
Number of 23S rrna genes in Gram-positive cocci S. pneumoniae 4 E. faecalis 4 S. aureus 5/6 S. agalactiae 6 S. pyogenes 6 E. faecium 6
Selection of linezolid-resistant mutants of E. faecalis JH2-2 and E. faecalis JH2-2 reca Linezolid MIC (mg/l) 1000 100 JH 2-2 JH 2-2 reca 10 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Day Boumghar-Bourtchai L, Leclercq R, Galopin S. Dhalluin A
Mutational resistance to linezolid E. faecalis No of passages Linezolid MIC (mg/l) G2576 mutation rrla rrlb rrlc rrld 0 2 G G G G JH2-2 4 8 G G G T 5 16 T G G T 6 32 T G G T 8 32 T G G/T T 0 2 G G G G JH2-2 reca 5 8 G G G T 6 8 G G G/T T Boumghar-Bourtchai L, Leclercq R, Galopin S. Dhalluin A 7 16 G G T T 8 16 G G T T
Linezolid dosage A single dose for everybody. from 40 kg to 200 kg.. Serum concentration of linezolid is proportional to the weight
Emergence of linezolid resistance in an in vitro pharmacodynamic model (Bacillus anthracis) Louie et al., Antimicrob Agents Chemother, 2008 June
Outbreak of Linezolid-Resistant Enterococci Kainer et al., Emerg Infect Dis, 2007;13: 1024-1030
Linezolid resistance due to ribosomal methylation The cfr gene encodes a rrna methylase, which transfers an additional methyl group to A2503 in 23S rrna Cfr impairs ribosomal binding of 5 different classes of antibiotics: phenicols lincosamides oxazolidinones pleuromutilins streptogramins A cfr is the first transferable gene for oxazolidinone and pleuromutilin resistance
Detection of linezolid Cfr resistance Arias et al, Antimicrob Agents Chemother, 2008, 46, 892
Transfer between animal and human staphylococci? Reported in Staphylococcus spp. of animal origin in Europe (Kehrenberg CF et al.. Antimicrob.Agents Chemother. 2007, 51:483 7. Kehrenberg C and S Schwarz. Antimicrob. Agents Chemother. 2006, 50:1156 63. Long KS et al.. Antimicrob. Agents Chemother. 2006, 50:2500 5. Schwarz, S., C. et al.. Antimicrob. Agents Chemother. 2000, 44:2530 3) And recently in staphylococci from humans. A unique human isolate in Colombia (Toh SM, Xiong L, Arias CA, Villegas MV, Lolans K, Quinn J, Mankin AS. Mol Microbiol. 2007;64:1506-14) A linezolid-resistant MRSA and one MR S. epidermidis were recently isolated in the USA (Mendes RE, et al. Antimicrob Agents Chemother. 2008;52:2244-6)
Mobilisation of cfr cfr surrounding DNA sequences in animal S. aureus (pscf53) and human S. aureus (004-737X) and S. epidermidis (426-3147L) isolates Mendes RE, et al. Antimicrob Agents Chemother. 2008;52:2244-6
The future of the «new» antimicrobials The «half-life» (in terms of clinical efficiency) of an antibiotic depends on numerous factors, including the existence of isolates with acquired resistance to the considered antibiotic at the starting point antibiotic usage the mechanism of resistance and the genetic support (plasmid..) Example of a recent modelisation for resistance to telithromycin (in pneumococci) (epidemiology and mechanisms of resistance known)
Opatowski L, Temime L, Varon E, Leclercq R, Drugeon H, Boëlle PY, Guillemot D. PLoS ONE. 2008;3:e2089 Antibiotic Innovation May Contribute to slowing the dissemination of MDR Streptococcus pneumoniae Times to reach 1% or 10% resistant strains among colonized individuals as a function of the rate of ketolide prescriptions
Conclusion Bacteria have already selected some specific ways to resist new antibiotics Tigecycline: efflux (Gram-positive and Gramnegative organisms Daptomycin: cell wall structure modification Linezolid: ribosomal target modification Resistant isolates are rare. Availibility of several antibiotic alternatives against MDR bacteria may delay the spread of resistance