Synergistic interaction in vitro with use of three antibiotics simultaneously against Pseudomonas maltophilia

J Infect Dis. 1980 Oct;142(4):602-7. doi: 10.1093/infdis/142.4.602.


An abbreviated three-dimensional checkerboard titration method was devised to determine whether synergistic interaction of three antimicrobial agents could be found against multidrug-resistant bacteria. Pseudomonas maltophilia was used as the test organism because of its resistance to most commercially available antimicrobial agents, including those active against Pseudomonas aeruginosa. Three-dimensional isobolograms with concave surfaces were formed when synergy occurred. Triple combinations of gentamicin-carbenicillin-rifampin (mean fractional inhibitory concentration index, 0.32) and trimethoprim/sulfamethoxazole-carbenicillin-rifampin (mean fractional inhibitory concentration index, 0.18) were consistently synergistic against 14 clinical isolates of P. maltophilia.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbenicillin / pharmacology*
  • Drug Synergism
  • Gentamicins / pharmacology*
  • Pseudomonas*
  • Rifampin / pharmacology*
  • Sulfamethoxazole / pharmacology
  • Time Factors
  • Trimethoprim / pharmacology


  • Gentamicins
  • Trimethoprim
  • Carbenicillin
  • Sulfamethoxazole
  • Rifampin