TABLE 1.

Activities of single antibiotics (MICs and MBCs) and antibiotic combinations (MCBT, checkerboard, or TK curve methodology) against isolates of P. aeruginosa

Patient no.P. aeruginosa isolateaActivity of treatment antibioticsbCombination bactericidal activity (MCBT)cResult of combination synergy testing
Antibiotic 1 in the combinationAntibiotic 2 in the combination
AgentMIC (mg/liter)MBC (mg/liter)AgentMIC (mg/liter)MBC (mg/liter)HighLowCheckerboard resultTK curve analysis result at 24 h
11ATM128>256TOB816YesNoSynergyIndifference
21aATM3264TOB816YesYesIndifferenceIndifference
1bATM64128TOB1616NoNoSynergySynergy
31CAZ1664TOB832NoNoSynergyIndifference
2CAZ1664TOB832YesNoSynergyIndifference
3CAZ1664TOB816NoNoSynergyIndifference
41aCAZ3232TOB88YesYesIndifferenceIndifference
1bCAZ832TOB44YesYesSynergyIndifference
1cCAZ88TOB48YesYesSynergyIndifference
51MEM816TOB44YesNoIndifferenceIndifference
61aMEM816TOB1616YesNoSynergyIndifference
1bMEM816TOB3232YesNoIndifferenceIndifference
2MEM816TOB816YesNoIndifferenceIndifference
3aMEM3232TOB3232YesNoIndifferenceSynergy
3bMEM1632TOB3232YesNoSynergySynergy
71TZP256128TOB3232NoNoIndifferenceIndifference
2TZP>25664TOB816NoNoIndifferenceIndifference
81CAZ128>256TZP>256>256NoNoIndifferenceNot tested
91CAZ32>128TOB48YesNoIndifferenceIndifference
2aCAZ32>128TOB48YesYesIndifferenceIndifference
2bCAZ32>128TOB816NoNoIndifferenceIndifference
3CAZ32>128TOB816NoNoSynergyIndifference
  • a The number refers to the morphotype, and the letter (a, b, or c) refers to the different isolates of that morphotype.

  • b ATM, aztreonam; CAZ, ceftazidime; MEM, meropenem; TOB, tobramycin; TZP, piperacillin-tazobactam.

  • c The result of combination bactericidal activity are yes, killed by the combination or a high concentration of a single antibiotic, and no, not killed. The concentrations used for the high-concentration MCBT were 32 mg/liter for aztreonam, 32 mg/liter for ceftazidime, 32 mg/liter for meropenem, 4 mg/liter for tobramycin, and 32/4 mg/liter for piperacillin-tazobactam; and those used for the low-concentration MCBT were 8 mg/liter for aztreonam, 8 mg/liter for ceftazidime, 4 mg/liter for meropenem, 4 mg/liter for tobramycin, and 16/2 mg/liter for piperacillin-tazobactam.