JAC Advance Access originally published online on October 29, 2003
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Journal of Antimicrobial Chemotherapy (2003) 52, 915-919
© 2003 The British Society for Antimicrobial Chemotherapy
In vitro activity and synergy of bismuth thiols and tobramycin against Burkholderia cepacia complex
Departments of 1 Pediatrics (Pulmonary Medicine and Neonatology) and 2 Medicine, and the 3 CardioPulmonary Research Institute, Winthrop University Hospital, SUNY Stony Brook School of Medicine, Mineola, NY; 4 Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, USA
Received 10 June 2003; returned 27 July 2003; revised 11 September 2003; accepted 13 September 2003
Objectives: To determine the susceptibility of Burkholderia multivorans and Burkholderia cenocepacia to bismuth-thiols (BTs), and to examine the synergistic effects of tobramycin and subinhibitory concentrations of BTs against these organisms.
Methods: The susceptibilities of 25 clinical isolates each of B. multivorans and B. cenocepacia to six BTs were measured by broth dilution in accordance with NCCLS protocols. Ten strains were selected to evaluate the antimicrobial interaction between BTs and tobramycin. Fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) indices were calculated to assess synergy.
Results: B. multivorans and B. cenocepacia showed a wide range of susceptibilities to BTs. Bismuth ethanedithiol (BisEDT) was one of the more potent BTs against these organisms (MIC50 7.8 µM), and was selected for synergy studies. Selected strains were highly resistant to tobramycin. The addition of subinhibitory concentrations of BisEDT (2 µM) reduced the MIC and MBC of tobramycin against all strains, achieving synergy in many instances. The FIC index was in the range 0.280.66 and the FBC in the range 0.120.85. Most strains became susceptible to tobramycin at clinically achievable concentrations in the presence of non-toxic BisEDT levels.
Conclusions: Treatment with subinhibitory BisEDT and tobramycin reduces the MICs and MBCs for B. multivorans and B. cenocepacia. BTs may represent an important adjunctive therapy for resistant Burkholderia cepacia complex.
Keywords: cystic fibrosis, antibiotics, biofilms, bacterial polysaccharide, aminoglycosides
* Correspondence address. CardioPulmonary Research Institute, Winthrop University Hospital, 222 Station Plaza North, Suite 505, Mineola, NY 1150, USA. Tel: +1-516-663-2654; E-mail: pdomenico{at}winthrop.org