Table 3.

Colistin and polymyxin disk diffusion QC results forE. coli ATCC 25922 and P. aeruginosa ATCC 27853 (120 to 200 observations)

Antimicrobial disk and QC strainNo. of positive isolates at zone diam (mm) of:% isolates in range
15 16 17 18 19 20 21 22PIaProposedb
Colistin
E. coli ATCC 25922 0 4a 33b 70b 12b 1b 0 0 0.0 100.0
P. aeruginosaATCC 27853 8b 36b 70b 6b 0b 0 0 0NDc 100.0
Polymyxin B
E. coli ATCC 25922 0 1a 9b 79b 89b 22b 0 0 0.5 99.5
P. aeruginosa ATCC 27853 0 0 3b 35b 90b 64b 7b 1ND 99.5
  • a PI, package insert range. Current PI ranges were: for colistin, E. coli ATCC 25922 at 11 to 15 mm, and for polymyxin B, E. coli ATCC 25922 at 12 to 16 mm.

  • b The proposed QC ranges from cited experiments were: for colistin, E. coli ATCC 25922 at 16 to 20 mm, andP. aeruginosa ATCC 27853 at 15 to 19 mm; for polymyxin B,E. coli ATCC 25922 at 17 to 20 mm, and for P. aeruginosa ATCC 27853 at 17 to 21 mm.

  • c PI zone diameter ranges were not defined (ND) for P. aeruginosa ATCC 27853.