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Table 1 Susceptibility category (susceptible or resistant) concordance of different assays compared to reference BMD method

From: Colistin resistance in Gram-negative bacteria analysed by five phenotypic assays and inference of the underlying genomic mechanisms

Method BMD Vitek 2®a Rapid PolymyxinTM NPb UMIC Colistin E-test MIC strip
Species S/R S/R % concordance S/R % concordance S/R % concordance S/R % concordance
Acinetobacter spp. 6/1 4/0 100 1/1 50 6/1 100 6/1 100
C. koseri 3/0 3/0 100 3/0 100 3/0 100 3/0 100
K. aerogenes 1/1 1/1 100 1/1 100 1/1 100 1/1 100
E. cloacae 2/3 3/2 80 2/3 100 2/3 100 3/2 80
E. coli 13/11 13/11 100 13/11 100 13/11 100 13/11 100
Hafnia spp. 0/15 1/14 93.3 0/15 100 0/15 100 0/15 100
K. oxytoca 1/2 1/2 100 1/2 100 1/2 100 1/2 100
K. pneumoniae 8/12 9/10 94.7 9/11 95 9/11 95 9/11 95
M. morganii 0/3 0/3 100 0/3 100 0/3 100 0/3 100
P. mirabilis 0/2 0/2 100 0/2 100 0/2 100 0/2 100
P. vulgaris 0/1 0/1 100 0/1 100 0/1 100 0/1 100
P. aeruginosa 9/1 8/0 87.5 NA NA 10/0 90 10/0 90
S. marcescens 0/2 0/2 100 0/2 100 0/2 100 0/2 100
Total 43/54 43/48 95.6 30/52 98.8 45/52 97.9 46/51 96.9
  1. BMD Broth microdilution, S Susceptible, R Resistant, NA Not applicable
  2. aA total of 91 isolates were tested by Vitek 2® method. Isolates not tested by Vitek 2® test was due to low growth, but were excluded from the comparison analysis with BMD
  3. bA total of 82 were tested by the Rapid PolymyxinTM NP method. Isolates not tested by Rapid PolymyxinTM NP test were excluded from the comparison analysis with gold standard