Table 1

Summary of colistin susceptibility test methods used in phase I and phase II of the study

TestaMethod referenceDescriptionTest mediumb (manufacturer)InoculumcStudy phase
ADCLSI M07 (12)In-house prepared AD platesMHA (BBL)0.5 McFarland suspension diluted in sterile saline to obtain 104 CFU/spotII
BMDCLSI M07 (12)In-house prepared BMD panels in untreated polystyrene microplatesCAMHB (Difco)0.5 McFarland suspension diluted in sterile water to obtain 3 × 105 to 5 × 105 CFU/mlII
BMD-TModification of CLSI M07 (12)In-house prepared BMD panels in untreated polystyrene microplatesCAMHB (Difco)0.5 McFarland suspension diluted in sterile water + 0.02% polysorbate 80 to obtain 3 × 105 to 5 × 105 CFU/ml; final polysorbate 80 concn, 0.002%I & II
TDSCLSI M07 (12)In-house prepared tube dilution in borosilicate tubes washed with Micro-90CAMHB (Difco)0.5 McFarland suspension diluted in CAMHB to obtain 3 × 105 to 5 × 105 CFU/mlI
EtestbioMérieux package insertAgar gradient diffusionMHA (BBL); MHA (Remel); MHA (Hardy)0.5 McFarland suspensionI
TREK GNXF Sensititre panelsTREK package insertDried MIC panelSensititre cation-adjusted Mueller-Hinton broth with TES buffer0.5 McFarland suspension diluted in deionized water to obtain 3 × 105 to 5 × 105 CFU/mlII
  • a AD, agar dilution; BMD, broth microdilution; BMD-T, broth microdilution with 0.002% polysorbate 80; TDS, broth macrotube dilution.

  • b MHA, Mueller-Hinton agar; CAMHB, cation-adjusted Mueller-Hinton broth; TES, N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid.

  • c The initial suspension of the organism was prepared in normal saline for all testing, with the exception of TREK GNXF, for which the suspension was prepared in deionized water.