clinical investigation| Volume 351, ISSUE 3, P265-270, March 2016

Download started.


In vitro Synergistic Activity of Caspofungin Plus Polymyxin B Against Fluconazole-Resistant Candida glabrata



      Candida species account for most invasive fungal infections, and the emergence of fluconazole and caspofungin resistance is problematic. Overcoming resistance with synergism between 2 drugs may be useful. In a 2013 in vitro study, caspofungin plus colistin (polymyxin E) was found to act synergistically against fluconazole-resistant and susceptible Candida albicans isolates. The purpose of our study was to extend this finding by evaluating caspofungin plus polymyxin B for in vitro synergy against fluconazole-resistant Candida glabrata isolates.

      Materials and Methods

      A total of 7 fluconazole-resistant C. glabrata bloodstream infection isolates were obtained from 2010–2011. Of these, 2 isolates were also resistant to caspofungin. Minimum inhibitory concentrations (MICs) for caspofungin and polymyxin B were determined by Etest and broth microdilution. Clinical and Laboratory Standards Institute breakpoints were used for fluconazole and caspofungin MIC interpretations. No interpretive guidelines exist for testing polymyxin B against C. glabrata. Synergy testing with caspofungin (1 × MIC) and polymyxin B (½MIC) was performed using a modified bacterial Etest synergy method and time-kill assay.


      With the Etest synergy method, 4 out of 7 isolates showed in vitro synergy and 1 out of 7 showed additivity. The remaining isolates (both caspofungin resistant) showed indifference. Using the time-kill assay, 1 out of 7 isolates showed synergy, 1 showed additivity and the remaining 5 (including both caspofungin-resistant isolates) showed indifference.


      Caspofungin susceptibility may be required for synergism between caspofungin and polymyxin B. Further synergy testing with caspofungin plus polymyxin B and additional fluconazole-resistant C. glabrata isolates should be performed. In vitro synergy/additivity may or may not correlate with in vivo benefit.

      Keying Indexing Terms

      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to The American Journal of the Medical Sciences
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Guinea J.
        Global trends in the distribution of Candida species causing candidemia.
        Clin Microbiol Infect. 2014; 20: 5-10
      1. Centers for Disease Control and Prevention. Antibiotic resistance threats in the United States, 2013. Atlanta (GA): US Department of Health and Human Services, CDC; 2013. Available at: Accessed 28.07.15.

        • Spampinato C.
        • Leonardi D.
        Candida infections, causes, targets, and resistance mechanisms: traditional and alternative antifungal agents.
        Biomed Res Int. 2013; 2013 (Article ID 204237)
        • Malani A.
        • Hmoud J.
        • Chiu L.
        • et al.
        Candida glabrata fungemia: experience in a tertiary care center.
        Clin Infect Dis. 2005; 41: 975-981
        • Lockhart S.R.
        Current epidemiology of Candida infection.
        Clin Microbiol Newsletter. 2014; 36: 131-136
        • Lockhart S.R.
        • Iqbal N.
        • Cleveland A.A.
        • et al.
        Species identification and antifungal susceptibility testing of Candida bloodstream isolates from population-based surveillance studies in two U.S. cities from 2008 to 2011.
        J Clin Microbiol. 2012; 50: 3435-3442
        • Pfaller M.A.
        • Messer S.A.
        • Boyken L.
        • et al.
        Variation in susceptibility of bloodstream isolates of Candida glabrata to fluconazole according to patient age and geographic location.
        J Clin Microbiol. 2003; 41: 2176-2179
        • Pfaller M.A.
        • Messer S.A.
        • Hollis R.J.
        • et al.
        Variation in susceptibility of bloodstream isolates of Candida glabrata to fluconazole according to patient age and geographic location in the United States in 2001 to 2007.
        J Clin Microbiol. 2009; 47: 3185-3190
        • Diekema D.
        • Arbefeville S.
        • Boyken L.
        • et al.
        The changing epidemiology of healthcare-associated candidemia over three decades.
        Diagn Microbiol Infect Dis. 2012; 73: 45-48
        • Pfaller M.A.
        • Castanheira M.
        • Lockhart S.R.
        • et al.
        Frequency of decreased susceptibility and resistance to echinocandins among fluconazole-resistant bloodstream isolates of Candida glabrata.
        J Clin Microbiol. 2012; 50: 1199-1203
        • Alexander B.D.
        • Johnson M.D.
        • Pfeiffer C.D.
        • et al.
        Increasing echinocandin resistance in Candida glabrata: clinical failure correlates with presence of FKS mutations and elevated minimum inhibitory concentrations.
        Clin Infect Dis. 2013; 56: 1724-1732
        • Pankey G.
        • Ashcraft D.
        • Kahn H.
        • et al.
        Time-kill assay and Etest evaluation for synergy with polymyxin B and fluconazole against Candida glabrata.
        Antimicrob Agents Chemother. 2014; 58: 5795-5800
        • Zeidler U.
        • Bougnoux M.E.
        • Lupan A.
        • et al.
        Synergy of the antibiotic colistin with echinocandin antifungals in Candida species.
        J Antimicrob Chemother. 2013; 68: 1285-1296
        • Zhai B.
        • Zhou H.
        • Yang L.
        • et al.
        Polymyxin B, in combination with fluconazole, exerts a potent fungicidal effect.
        J Antimicrob Chemother. 2010; 65: 931-938
        • Ogita A.
        • Konishi Y.
        • Borjihan B.
        • et al.
        Synergistic fungicidal activities of polymyxin B and ionophores, and their dependence on direct disruptive action of polymyxin B on fungal vacuole.
        J Antibiot. 2009; 62: 81-87
        • Moneib N.A.
        In-vitro activity of commonly used antifungal agents in the presence of rifampin, polymyxin B and norfloxacin against Candida albicans.
        J Chemother. 1995; 7: 525-529
        • Clinical and Laboratory Standards Institute
        Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts: 4Th Informational Supplement.
        ([CLSI document M27-S4]) CLSI, Wayne (PA)2012
        • Clinical and Laboratory Standards Institute
        Performance Standards for Antimicrobial Susceptibility Testing: 25Th Informational Supplement.
        ([CLSI document M100-S25]) CLSI, Wayne (PA)2015
        • Clinical and Laboratory Standards Institute
        Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts: Approved Standard.
        3rd ed. CLSI, [CLSI document M27-A3]. Wayne (PA)2008
        • Pillai S.K.
        • Moellering Jr, R.C.
        • Eliopoulos G.M.
        Antimicrobial combinations.
        in: Lorian V. Antibiotics in Laboratory Medicine. 5th ed. Lippincott Williams and Wilkins, Philadelphia2005: 365-405
        • Klepser M.E.
        • Ernst E.J.
        • Lewis R.E.
        • et al.
        Influence of test conditions on antifungal time-kill curve results: proposal for standardized methods.
        Antimicrob Agents Chemother. 1998; 42: 1207-1212
        • Kanafani Z.A.
        • Perfect J.R.
        Antimicrobial resistance: resistance to antifungal agents: mechanisms and clinical impact.
        Clin Infect Dis. 2008; 46: 120-128
        • Lorian V.
        In vitro simulation of in vivo conditions: physical state of the culture medium.
        J Clin Microbiol. 1989; 27: 2403-2406