Summary of CBDE results compared to rBMD and BMD results in a two-site studyc

Site and isolateNo. of isolates with the following BMD result:CA (%)EA (%)VME (%)ME (%)
TotalS or WT (N)R or NWT (N)
Site 1
    Acinetobacter baumannii125710010000
    Pseudomonas aeruginosa2018210010000
Site 2
    Retrospective CRE6558710097a00
    A. baumannii1212010010000
    P. aeruginosa1414010010000
    Prospective CRE1917210010000
Both sites, mcr-1-producing E. colib60650100500
  • a One Citrobacter freundii isolate had an MIC of ≤0.25 µg/ml by BMD and an MIC of 2 µg/ml by CBDE, and 1 Enterobacter cloacae isolate had an MIC of 0.5 µg/ml by BMD and an MIC of 2 µg/ml by CBDE.

  • b Three mcr-1-positive E. coli isolates had MICs of 4 µg/ml by BMD and 2 µg/ml by CBDE on initial testing at both sites. These results were reproduced at the 2 sites.

  • c S, susceptible; R, resistant; WT, wild type; NWT, non-wild type; N, number of isolates; CA, categorical agreement; EA, essential agreement; VME, very major error; ME, major error; BMD, broth microdilution; rBMD, reference BMD. Site 1 performed rBMD and site 2 performed BMD. At site 1, the Enterobacteriaceae consisted of 8 Klebsiella pneumoniae isolates (3 were carbapenem resistant), 7 E. cloacae isolates, 4 Escherichia coli isolates, 2 Klebsiella (Enterobacter) aerogenes isolates, 1 C. freundii isolate, 1 Citrobacter koseri isolate, and 1 Enterobacter hermannii isolate. At site 2, the retrospective CRE consisted of 32 K. pneumoniae isolates, 15 E. cloacae isolates, 8 E. coli isolates, 4 C. freundii isolates, 3 Serratia marcescens isolates, 1 Proteus mirabilis isolate, 1 K. aerogenes isolate, and 1 Klebsiella oxytoca/Raoultella ornithinolytica isolate. At site 2, prospective carbapenem-resistant Enterobacteriaceae consisted of 13 Klebsiella pneumoniae isolates, 3 E. cloacae isolates, and 3 Escherichia coli isolates.