Comparison of methods for MBL detection

EnzymeOrganism (no. of isolates)No. of isolates with positive result or no. of positive isolates/total no. of isolates evaluated by the following test:
IPMMEM with TE + MPA disksaTE + 1:80 MPA disks
TE disk alonebMPA disk alonecTE + MPA disksa1:80 MPA1:320 MPA1:640 MPAERTCAZ
1:80 MPAd1:320 MPA1:640 MPA
    IMP-1A. baumannii (2)0222222221
    IMP-1-likeS. marcescens (1)1111111111
    IMP-18P. aeruginosa (1)1111111101
    VIM-2A. baumannii (2)2222222222
P. aeruginosa (2)2222122112
    VIM-2-likeP. aeruginosa (1)1011111001
    GIM-1P. aeruginosa (1)1e111110001
    SPM-1P. aeruginosa (1)0111010001
    ChromosomalA. hydrophila (1)NDfNDND1NDNDNDNDNDND
    ChromosomalA. veronii (1)NDNDND1NDNDNDNDNDND
    ChromosomalC. meningosepticum (2)NDNDND2NDNDNDNDNDND
    ChromosomalS. maltophilia (1)NDNDND1NDNDNDNDNDND
    ACT-1K. pneumoniae (1)NDgND100000NDND
    ACT-1 + ESBLK. pneumoniae (1)NDND000000NDND
    CMYE. coli (1)NDND100100NDND
    DHA-1K. pneumoniae (1)NDND000100NDND
    FOXK. pneumoniae (1)NDND100100NDND
    LATE. coli (1)NDND100110NDND
    AmpC + porin mutationE. cloacae (1)NDND000000NDND
    SHV-5-likeK. pneumoniae (1)NDND100000NDND
    TEM ESBLP. mirabilis (1)NDND100100NDND
    VEB-3E. cloacae (1)NDND100100NDND
    IMI-1E. cloacae (1)NDND000000NDND
    KPC-2K. pneumoniae (1)NDND100000NDND
    KPC-2 + ESBLK. pneumoniae (1)NDND000000NDND
    KPC-3E. coli (1)NDND000000NDND
    NMC-AE. cloacae (2)NDND100220NDND
    SME-likeS. marcescens (2)NDND000220NDND
    OXA-23A. baumannii (2)NDND000000NDND
% Sensitivity72.790.910010081.810081.863.654.590.9
% SpecificityNDhND551001005075100NDND
  • a The overall sensitivities and specificities of DDTs with 1:160 MPA were 100 and 80%, respectively, for the IPM-based tests and 100 and 60%, respectively, for the MEM-based tests. The sensitivities and specificities for the 1:1,280 MPA-based tests were the same as those with 1:640 MPA.

  • b TE alone, tests with both standard BD-manufactured TE disks and also disks to which additional TE solution (1:16 or undiluted) was added.

  • c MPA alone, tests with blank disks to which MPA solution (1:80 or 1:320) was added.

  • d The MPA dilutions tested were 1:80, 1:160, 1:320, 1:640, and 1:1,280.

  • e The unsupplemented TE disk failed to detect one GIM-1-producing P. aeruginosa isolate, whereas the high-strength TE disk detected this isolate.

  • f ND, tests with chromosomal MBL producers were not done by these methods because they were shown to be suboptimal with isolates that produced plasmid-mediated MBLs.

  • g ND, tests with non-MBL producers were not done because initial tests with MBL-producing isolates indicated that this test was too insensitive for further investigation.

  • h ND, specificity could not be determined.