TABLE 3.

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

Antimicrobial disk and QC strain	No. of positive isolates at zone diam (mm) of:								% isolates in range
	15	16	17	18	19	20	21	22	PIa	Proposedb
Colistin
E. coli ATCC 25922	0	4a	33b	70b	12b	1b	0	0	0.0	100.0
P. aeruginosa ATCC 27853	8b	36b	70b	6b	0b	0	0	0	NDc	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	1	ND	99.5

^aPI, 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. 

^bThe proposed QC ranges from cited experiments were: for colistin, E. coli ATCC 25922 at 16 to 20 mm, and P. 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. 

^cPI zone diameter ranges were not defined (ND) for P. aeruginosa ATCC 27853.