Fig. 1

Representative results of the RCPE and RCPEm tests

(A) Representative results of Rapid colorimetric polymyxin B elution (RPCE) test at every hour of reading, for up to 4 h, with growth being evidenced from color change (orange to yellow). For each image of two tubes, the tube on the right contains the eluted polymyxin B disk, reaching a concentration of 2 µg/mL. I: Susceptible isolate due to permanence of orange color in a tube containing antibiotic disk. II: Resistant isolate due to color change of tube containing antibiotic disk. (B) Rapid colorimetric polymyxin B microelution (RCPEm) test results at each hour of reading for up to 4 h. The color change of the wells from orange to yellow indicates bacterial growth. I: Antibiotic-free column of wells (growth control). II: Column of wells with NP solution where antibiotic disks were previously eluted, resulting in a final concentration of 3 µg/mL of polymyxin B. III: Resistant isolate due to color change in the well containing the antibiotic. IV: Sensitive isolate due to continuity of orange staining of an antibiotic-containing well