In Vitro Synergy of Daptomycin plus Rifampin against Enterococcus faecium Resistant to both Linezolid and Vancomycin

Please download to get full document.

View again

of 4
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Document Description
In Vitro Synergy of Daptomycin plus Rifampin against Enterococcus faecium Resistant to both Linezolid and Vancomycin
Document Share
Document Tags
Document Transcript
    10.1128/AAC.49.12.5166-5168.2005. 2005, 49(12):5166. DOI: Antimicrob. Agents Chemother. George Pankey, Deborah Ashcraft and Nalini Patel  VancomycinResistant to both Linezolid and Enterococcus faecium  Rifampin against In Vitro Synergy of Daptomycin plus information and services can be found at: These include:  REFERENCES This article cites 18 articles, 12 of which can be accessed free CONTENT ALERTS  more»articles cite this article), Receive: RSS Feeds, eTOCs, free email alerts (when new Information about commercial reprint orders: To subscribe to to another ASM Journal go to:  on O c  t   o b  er  6  ,2  0 1 4  b  y  g u e s  t  h  t   t   p:  /   /   a a c . a s m. or  g /  D  ownl   o a d  e d f  r  om  on O c  t   o b  er  6  ,2  0 1 4  b  y  g u e s  t  h  t   t   p:  /   /   a a c . a s m. or  g /  D  ownl   o a d  e d f  r  om    A  NTIMICROBIAL   A  GENTS AND  C HEMOTHERAPY , Dec. 2005, p. 5166–5168 Vol. 49, No. 120066-4804/05/$08.00  0 doi:10.1128/AAC.49.12.5166–5168.2005Copyright © 2005, American Society for Microbiology. All Rights Reserved. In Vitro Synergy of Daptomycin plus Rifampin against  Enterococcus faecium  Resistant to both Linezolid and Vancomycin George Pankey,* Deborah Ashcraft, and Nalini Patel Ochsner Clinic Foundation, New Orleans, Louisiana Received 20 May 2005/Returned for modification 21 August 2005/Accepted 27 September 2005 In vitro synergy testing of daptomycin plus rifampin was performed against 24 unique isolates of   Entero- coccus faecium  resistant to both linezolid and vancomycin. Synergy testing showed that 21/24 (88%) weresynergistic and 3/24 (12%) were indifferent by the Etest method. Time-kill assays revealed synergy for 18/24(75%) and indifference for 6/24 (25%). Therapeutic failure due to antimicrobial-resistant gram-pos-itive pathogens, such as linezolid- and vancomycin-resistant  Enterococcus faecium , is increasing. In an attempt to improveefficacy, an antimicrobial combination is frequently adminis-tered on an empirical basis. Many antimicrobial combinationshave been studied for synergy in vitro and in vivo againstenterococci (4, 9, 17, 19, 20), with no demonstrated correla-tion. We studied the in vitro combination of daptomycin(DAP) and rifampin (RIF) against linezolid- and vancomycin-resistant  E. faecium .Daptomycin has good in vitro activity against gram-positivebacteria, including vancomycin-resistant enterococci (1, 5, 8,10–12, 21). Rifampin has shown synergy with other drugs inanimal models for the treatment for gram-positive infections(2, 3, 7, 16, 17). In a synergy study with vancomycin-resistant  E. faecium  by Rand and Houck, it was suggested that, at subin-hibitory daptomycin concentrations, daptomycin might bind tothe bacterial cell, opening a channel that allows rifampin entry(19).Standard laboratory powders of DAP (Cubist Pharmaceuti-cals, Inc., Lexington, MA) and RIF (Sigma-Aldrich, St. Louis,MO) were used in this study. Etest strips (AB Biodisk, Solna,Sweden) of daptomycin and rifampin were also used. Thedaptomycin Etest contained a concentration gradient of dap-tomycin with a standard amount of calcium throughout thestrip.Twenty-four unique clinical  Enterococcus faecium  isolates with distinct plasmid DNA (by pulsed-field gel electrophoresis)that were resistant to both linezolid (Etest MICs, 8 to   256  g/ml) and vancomycin (Etest MICs,   256   g/ml) were col-lected from throughout the United States. All strains wereidentified by the Vitek system (bioMerieux Inc., Hazelwood,MO). Isolates were stored frozen at  70°C in Columbia broth with 20% glycerol.  Enterococcus faecalis  ATCC 29212 was in-cluded as a quality control strain (6). Mueller-Hinton II broth(Becton Dickinson Microbiology Systems, Sparks, MD) wasprepared in the laboratory and supplemented to the recom-mended 50 mg/liter calcium for the testing of daptomycin (15).Mueller-Hinton II agar plates (Becton Dickinson Microbiol-ogy Systems, Sparks, MD) were used for the Etest MIC deter-mination and the Etest synergy method. Trypticase soy agar with 5% sheep blood (Becton Dickinson Microbiology Sys-tems, Sparks, MD) was used for the colony counts in thetime-kill assay.Daptomycin and rifampin MICs were determined by brothmicrodilution (BMD) and Etest. The Clinical and LaboratoryStandards Institute (CLSI [formerly NCCLS]) interpretivestandards for rifampin and enterococci are as follows:  1  g/ ml, susceptible; 2  g/ml, intermediate;  4  g/ml, resistant; fordaptomycin and enterococci, the CLSI standard is that   4  g/ml implies susceptibility (6).BMD MICs were determined following 2003 CLSI guide-lines (15). Etest MICs for daptomycin and rifampin were de-termined in triplicate, and testing was performed according tothe manufacturer’s instructions. MICs between twofold dilu-tions were rounded up to the next twofold dilution for pur-poses of comparison with the BMD MIC.Synergy testing was performed using an Etest method (18)and time-kill assay (TKA). The Etest method was performed intriplicate, the summation fractional inhibitory concentration(  FIC) was calculated for each set of MICs, and the mean  FIC was used for comparison to the TKA.To evaluate the effect of the combinations, the FIC wascalculated for each antibiotic in each combination. High-off-scale MICs (  256  g/ml) were converted to the next twofolddilution (512   g/ml). The following formulas were used tocalculate the   FIC: (i) FIC of drug A     MIC of drug A incombination/MIC of drug A alone; (ii) FIC of drug B  MICof drug B in combination/MIC of drug B alone; (iii)   FIC   FIC of drug A   FIC of drug B.Synergy was defined by a   FIC of    0.5. Antagonism wasdefined by a  FIC of   4. Interactions represented by a  FICof   0.5 but  4 were termed indifferent (1a).The TKA was chosen to be compared with the Etest methodfor all isolates following guidelines set by the CLSI (14) and was performed as described in our previous study (18). Eachisolate was tested against daptomycin and rifampin alone andin combination at a concentration equal to the MIC to corre-late with the Etest. Bottles were incubated at 35°C in ambientair for 24 h. Samples (0.5 ml) were removed from each bottleat 0 h and 24 h. TKA results which were discordant to the Etestmethod results were repeated and confirmed the initial TKA  * Corresponding author. Mailing address: Ochsner Clinic Founda-tion, 1514 Jefferson Highway, New Orleans, LA 70121. Phone: (504)842-4006. Fax: (504) 842-5433. E-mail:   on O c  t   o b  er  6  ,2  0 1 4  b  y  g u e s  t  h  t   t   p:  /   /   a a c . a s m. or  g /  D  ownl   o a d  e d f  r  om   interpretation. Performing serial dilutions, plating with a spiralplater (which further dilutes and plates the sample), and usinga concentration of drug equal to the MIC helped reduce thepossibility of antibiotic carryover. Synergy was defined as a  2log 10  decrease in colony count at 24 h by the combinationcompared to the most active single agent, and the number of surviving organisms in the presence of the combination had tobe   2 log 10  CFU/ml below the starting inoculum (1a). Indif-ference was defined as   2 log 10  increase in colony count at24 h by the combination compared by the most active singleagent. Antagonism was defined as a  2 log 10  increase in colonycount at 24 h by the combination compared with that by themost active single agent alone (13).Some isolates showed resistance to rifampin: 15/24 (63%) bybroth microdilution and 16/24 (67%) by Etest. All isolates weresusceptible to daptomycin by both methods (Table 1).The daptomycin Etest had 88% (21/24)  1 twofold dilutionessential agreement with daptomycin BMD, suggesting ade-quate calcium content of the Etest strip when used with BectonDickinson Mueller-Hinton II agar plates. The rifampin Etesthad only 58% (14/24) essential agreement with rifampin BMD.The rifampin BMD MICs were lower for 17/24 (71%) isolates,higher for 5/24 (21%) isolates, and identical for 2/24 (8%)isolates when compared to rifampin Etest MICs.Daptomycin and rifampin synergy (  FIC    0.5) was foundin 20/24 (83%) strains when tested by Etest. The TKA revealed75% (18/24) synergy and 25% (6/24) indifference. Concor-dance of the Etest synergy method and the TKA was demon-strated in 15/24 (63%) isolates. For three isolates, the Etestmethod   FICs were 0.6, 0.9, and 1.0 (indifference) but theTKA showed synergy. Six isolates showed synergy, with  FICsof 0.2, 0.4, 0.2, 0.4, 0.3, and 0.2 but were indifferent by TKA (  1.4,  0.9,  1.4,  0.6,  1.0, and  0.5 log 10  change, respec-tively, in CFU/ml). The synergy occurred despite significantdaptomycin activity against all isolates. No antagonism wasdetected by either method (Table 1).Synergy testing methods are not standardized for reproduc-ibility and interpretation, making comparison of results fromdifferent studies extremely difficult.In the TKA for synergy, drug concentrations are fixed anddo not decrease over time, as they would in vivo. In addition,there are no standard concentrations at which antibiotics aretested. The inoculum size and time frame of the TKA addmore variability to the test. The time parameter of 24 h canlimit or alter results of the experiment if regrowth occurs withone or both antibiotics. Regrowth can be caused by use of asubinhibitory concentration of antibiotics, emergence of resis-tant subpopulations, or bacteria that adhere to the surface of the bottle and are subsequently released in the media. Anotherfactor affecting regrowth is inactivation of the antibiotics in vitro.The Etest synergy method used a concentration equal to theMIC for each drug. Depending on the drug, concentrationranges vary on Etest strips. A MIC-to-MIC placement of thestrips seems to give a more accurate diffusion of the two drugsand indication of the effects (if any) that each drug has on theother in combination against the organism (18). Several ab-stracts have been presented on the technique using gram-positive bacteria: G. Pankey and D. Ashcraft, Abstr. 101st Gen.Meet. Am. Soc. Microbiol., abstr. C92, 2001; G. Pankey, D. TABLE 1. MICs by Etest and broth microdilution and synergy testing by Etest and time-kill assay  E. faecium  isolate(  n  24)MIC (  g/ml) of: Synergy testingDAP by: RIF by: Etest  b TKA log 10 change  a Etest  b BMD Etest  b BMD   FICs Mean  FIC 1 4 2 0.008 0.032 0.3, 0.5, 0.8 0.6   2.0 (SYN)2 4 1 16 8 0.1, 0.1, 0.1 0.1   2.0 (SYN)3 2 2 0.032 0.064 0.9, 0.9, 0.9 0.9   2.0 (SYN)4 2 2 0.016 0.064 0.2, 0.2, 0.3 0.2   4.0 (SYN)5 2 2 0.016   0.016 0.3, 0.2, 0.2 0.2   5.0 (SYN)6 1 2 16 16 0.2, 0.3, 0.2 0.2   2.4 (SYN)7 2 2 16 8 0.3, 0.3, 0.3 0.3   2.0 (SYN)8 2 2 0.016 0.032 0.3, 0.3, 0.2 0.3   2.1 (SYN)9 2 2   256   32 0.4, 0.4, 0.3 0.4   2.0 (SYN)10 2 1 8 1 0.2, 0.3, 0.4 0.3   2.0 (SYN)11 2 2 32 8 0.2, 0.2, 0.3 0.2   2.0 (SYN)12 2 4 32 16 0.2, 0.4, 1.0 0.5   2.6 (SYN)13 4 4 32 8 0.1, 0.4, 0.2 0.2   2.0 (SYN)14 2 2 0.016 0.032 0.4, 0.3, 0.4 0.4   2.5 (SYN)15 1 1 16 4 0.4, 0.4, 0.3 0.4   2.2 (SYN)16 2 0.5 16 4 0.3, 0.2, 0.2 0.2   2.0 (SYN)17 4 2 32 16 0.2, 0.2, 0.2 0.2   2.0 (SYN)18 4 1 0.032 0.032 1.0, 1.0, 1.0 1.0   2.0 (SYN)19 2 1 32 4 0.2, 0.2, 0.1 0.2   1.4 (IND)20 4 2 0.016   0.016 0.4, 0.3, 0.5 0.4   0.9 (IND)21 2 2 16 4 0.1, 0.2, 0.2 0.2   1.4 (IND)22 2 1 8 4 0.4, 0.4, 0.3 0.4   0.6 (IND)23 2 1 32 8 0.3, 0.3, 0.3 0.3   1.0 (IND)24 4 2 8 4 0.2, 0.2, 0.3 0.2   0.5 (IND)  a Values represent the log 10  change (CFU/ml) in the TKA after 24-h exposure to DAP and RIF when compared to the most active drug alone. Negative valuesindicate a decrease in colony count. SYN, synergy; IND, indifference.  b Performed in triplicate. V OL  . 49, 2005 NOTES 5167   on O c  t   o b  er  6  ,2  0 1 4  b  y  g u e s  t  h  t   t   p:  /   /   a a c . a s m. or  g /  D  ownl   o a d  e d f  r  om    Ashcraft, and O. Prakash, Abstr. 42nd Intersci. Conf. Antimi-crob. Agents Chemother., abstr. E-1133, 2002; and G. Pankey,D. Ashcraft, and P. Pankey, Abstr. 41st Infect. Dis. Soc. Am.,abstr. 229, 2003. The use of the Etest strips for synergy has yetto be standardized but has the potential to be a useful screen-ing test for the determination of synergy.Our Etest method was compared to TKA, but the two meth-ods use totally different test systems, solid media versus liquid,respectively. However, both methods predict bactericidal ac-tivity in vitro. The Etest was able to detect slight hazes of growth and resistant subpopulations.It is interesting that we could demonstrate in vitro synergy of daptomycin and rifampin against some  E. faecium  isolates.However, the mechanism of this in vitro synergy is unknown.The clinical benefit of in vitro synergy by daptomycin andrifampin against any strain of   E. faecium  remains speculation.(Part of these data were presented at the 42nd annual meet-ing of the Infectious Diseases Society of America, Boston, MA,October 2004.) We thank Royanne Vortisch for laboratory assistance, Marion Staf-ford for editorial support, Pat Pankey for laboratory management, andRichard Goering, Department of Medical Microbiology and Immu-nology, Creighton University School of Medicine, Omaha, NE, forperforming the pulsed-field gel electrophoresis on the  E. faecium  iso-lates.This study was funded by a grant from Cubist Pharmaceuticals, Inc. REFERENCES 1.  Akins, R. L., and M. J. Rybak.  2001. Bactericidal activities of two daptomycinregimens against clinical strains of glycopeptide intermediate-resistant Staphylococcus aureus , vancomycin-resistant  Enterococcus faecium , and me-thicillin-resistant  Staphylococcus aureus  isolates in an in vitro pharmacody-namic model with simulated endocardial vegetations. Antimicrob. AgentsChemother.  45: 454–459.1a.  Anonymous.  2005. Instructions to authors. Antimicrob. Agents Chemother. 49: 1–20.2.  Archer, G. L., J. L. Johnston, G. J. Vazquez, and H. B. Haywood III.  1983.Efficacy of antibiotic combinations including rifampin against methicillin-resistant  Staphylococcus epidermidis : in vitro and in vivo studies. Rev. Infect.Dis.  5 (Suppl. 3) : S538–S542.3.  Brandt, C. M., M. S. Rouse, B. M. Tallan, N. W. Laue, W. R. Wilson, and J. M. Steckelberg.  1995. Effective treatment of cephalosporin-rifampin com-binations against cryptic methicillin-resistant beta-lactamase-producing co-agulase-negative staphylococcal experimental endocarditis. Antimicrob. Agents Chemother.  39: 1815–1819.4.  Caron, F., M. D. Kitzis, L. Gutmann, A. C. Cremieux, B. Maziere, J. M. Vallois, A. Saleh-Hghir, J. F. Lemeland, and C. Carbon.  1992. Daptomycinor teicoplanin in combination with gentamicin for treatment of experimentalendocarditis due to a highly glycopeptide-resistant isolate of   Enterococcus faecium . Antimicrob. Agents Chemother.  36: 2611–2616.5.  Cha, R., R. G. Gruez, Jr., and M. J. Rybak.  2003. Daptomycin dose-effectrelationship against resistant gram-positive organisms. Antimicrob. AgentsChemother.  47: 1598–1603.6.  Clinical and Laboratory Standards Institute.  2005. Performance standardsfor antimicrobial susceptibility testing. Fifteenth informational supplement.CLSI document M100-S15. Clinical and Laboratory Standards Institute,Wayne, Pa.7.  Craven, N., and J. C. Anderson.  1981. Therapy of experimental staphylococ-cal mastitis in the mouse with cloxacillin and rifampicin, alone and in com-bination. Res. Vet. Sci.  31: 295–300.8.  Critchley, I. A., R. S. Blosser-Middleton, M. E. Jones, C. Thornsberry, D. F.Sahm, and J. A. Karlowsky.  2003. Baseline study to determine in vitroactivities of daptomycin against gram-positive pathogens isolated in theUnited States in 2000–2001. Antimicrob. Agents Chemother.  47: 1689–1693.9.  Dawis, M. A., H. D. Isenberg, K. A. France, and S. G. Jenkins.  2003. In vitroactivity of gatifloxacin alone and in combination with cefepime, meropenem,piperacillin and gentamicin against multidrug-resistant organisms. J. Anti-microb. Chemother.  51: 1203–1211.10.  Johnson, A. P., S. Mushtaq, M. Warner, and D. M. Livermore.  2004. Activityof daptomycin against multiresistant gram-positive bacteria including entero-cocci and  Staphylococcus aureus  resistant to linezolid. Int. J. Antimicrob. Agents  24: 315–319.11.  Jorgensen, J. H., S. A. Crawford, C. C. Kelly, and J. E. Patterson.  2003. In vitro activity of daptomycin against vancomycin-resistant enterocooci of var-ious Van types and comparison of susceptibility testing methods. Antimi-crob. Agents Chemother.  47: 3760–3773.12.  Lewis, R. E., D. J. Diekema, S. A. Messer, M. A. Pfaller, and M. E. Klepser. 2002. Comparison of Etest, chequerboard dilution and time-kill studies forthe detection of synergy or antagonism between antifungal agents testedagainst  Candida  species. J. Antimicrob. Chemother.  49: 345–351.13.  Lorian, V. (ed.).  1996. Antibiotics in laboratory medicine, 4th ed. Williams &Wilkins, Baltimore, Md.14.  NCCLS.  1999. Methods for determining bactericidal activity of antimicrobialagents. NCCLS document M26-A. NCCLS, Wayne, Pa.15.  NCCLS.  2003. Methods for dilution antimicrobial susceptibility tests forbacteria that grow aerobically. NCCLS document M7-A6. NCCLS, Wayne,Pa.16.  Norden, C. W.  1983. Experimental chronic staphylococcal osteomyelitis inrabbits: treatment with rifampin alone and in combination with other anti-microbial agents. Rev. Infect. Dis.  5 (Suppl. 3) : S491–S494.17.  Oill, P. A., G. M. Kalmanson, and L. B. Guze.  1981. Rifampin, ampicillin,streptomycin, and their combinations in the treatment of enterococcal pye-lonephritis in rats. Antimicrob. Agents Chemother.  20: 491–492.18.  Pankey, G. A., and D. S. Ashcraft.  2005. In vitro synergy of ciprofloxacin andgatifloxacin against ciprofloxacin-resistant  Pseudomonas aeruginosa . Antimi-crob. Agents Chemother.  49: 2959–2964.19.  Rand, K. H., and H. Houck.  2004. Daptomycin synergy with rifampin andampicillin against vancomycin-resistant enterococci. J. Antimicrob. Che-mother.  53: 530–532.20.  Smith, C. E., B. E. Foleno, J. F. Barrett, and M. B. Frosco.  1997. Assessmentof the synergistic interactions of levofloxacin and ampicillin against  Entero- coccus faecium  by the checkerboard agar dilution and time-kill methods.Diagn. Microbiol. Infect. Dis.  27: 85–92.21.  Streit, J. M., R. N. Jones, and H. S. Sader.  2004. Daptomycin activity andspectrum: a worldwide sample of 6737 clinical gram-positive organisms. J. Antimicrob. Chemother.  53: 669–674. 5168 NOTES A  NTIMICROB . A  GENTS  C HEMOTHER .   on O c  t   o b  er  6  ,2  0 1 4  b  y  g u e s  t  h  t   t   p:  /   /   a a c . a s m. or  g /  D  ownl   o a d  e d f  r  om 
Similar documents
View more...
Search Related
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks