TABLE 1.
Comparison of methods for MBL detection
| Enzyme | Organism (no. of isolates) | No. of isolates with positive result or no. of positive isolates/total no. of isolates evaluated by the following test:
|
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| IPM
|
MEM with TE + MPA disksa
|
TE + 1:80 MPA disks
|
|||||||||
| TE disk aloneb | MPA disk alonec | TE + MPA disksa
|
1:80 MPA | 1:320 MPA | 1:640 MPA | ERT | CAZ | ||||
| 1:80 MPAd | 1:320 MPA | 1:640 MPA | |||||||||
| MBLs | |||||||||||
| IMP-1 | A. baumannii (2) | 0 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 1 |
| IMP-1-like | S. marcescens (1) | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| IMP-18 | P. aeruginosa (1) | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 |
| VIM-2 | A. baumannii (2) | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| P. aeruginosa (2) | 2 | 2 | 2 | 2 | 1 | 2 | 2 | 1 | 1 | 2 | |
| VIM-2-like | P. aeruginosa (1) | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 |
| GIM-1 | P. aeruginosa (1) | 1e | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 1 |
| SPM-1 | P. aeruginosa (1) | 0 | 1 | 1 | 1 | 0 | 1 | 0 | 0 | 0 | 1 |
| Chromosomal | A. hydrophila (1) | NDf | ND | ND | 1 | ND | ND | ND | ND | ND | ND |
| Chromosomal | A. veronii (1) | ND | ND | ND | 1 | ND | ND | ND | ND | ND | ND |
| Chromosomal | C. meningosepticum (2) | ND | ND | ND | 2 | ND | ND | ND | ND | ND | ND |
| Chromosomal | S. maltophilia (1) | ND | ND | ND | 1 | ND | ND | ND | ND | ND | ND |
| Total | (16) | 8/11 | 10/11 | 11/11 | 16/16 | 9/11 | 11/11 | 9/11 | 7/11 | 6/11 | 10/11 |
| Non-MBLs | |||||||||||
| ACT-1 | K. pneumoniae (1) | NDg | ND | 1 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| ACT-1 + ESBL | K. pneumoniae (1) | ND | ND | 0 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| CMY | E. coli (1) | ND | ND | 1 | 0 | 0 | 1 | 0 | 0 | ND | ND |
| DHA-1 | K. pneumoniae (1) | ND | ND | 0 | 0 | 0 | 1 | 0 | 0 | ND | ND |
| FOX | K. pneumoniae (1) | ND | ND | 1 | 0 | 0 | 1 | 0 | 0 | ND | ND |
| LAT | E. coli (1) | ND | ND | 1 | 0 | 0 | 1 | 1 | 0 | ND | ND |
| AmpC + porin mutation | E. cloacae (1) | ND | ND | 0 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| SHV-5-like | K. pneumoniae (1) | ND | ND | 1 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| TEM ESBL | P. mirabilis (1) | ND | ND | 1 | 0 | 0 | 1 | 0 | 0 | ND | ND |
| VEB-3 | E. cloacae (1) | ND | ND | 1 | 0 | 0 | 1 | 0 | 0 | ND | ND |
| IMI-1 | E. cloacae (1) | ND | ND | 0 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| KPC-2 | K. pneumoniae (1) | ND | ND | 1 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| KPC-2 + ESBL | K. pneumoniae (1) | ND | ND | 0 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| KPC-3 | E. coli (1) | ND | ND | 0 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| NMC-A | E. cloacae (2) | ND | ND | 1 | 0 | 0 | 2 | 2 | 0 | ND | ND |
| SME-like | S. marcescens (2) | ND | ND | 0 | 0 | 0 | 2 | 2 | 0 | ND | ND |
| OXA-23 | A. baumannii (2) | ND | ND | 0 | 0 | 0 | 0 | 0 | 0 | ND | ND |
| Total | (20) | 9 | 0 | 0 | 10 | 5 | 0 | ||||
| % Sensitivity | 72.7 | 90.9 | 100 | 100 | 81.8 | 100 | 81.8 | 63.6 | 54.5 | 90.9 | |
| % Specificity | NDh | ND | 55 | 100 | 100 | 50 | 75 | 100 | ND | ND | |
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.
TE alone, tests with both standard BD-manufactured TE disks and also disks to which additional TE solution (1:16 or undiluted) was added.
MPA alone, tests with blank disks to which MPA solution (1:80 or 1:320) was added.
The MPA dilutions tested were 1:80, 1:160, 1:320, 1:640, and 1:1,280.
The unsupplemented TE disk failed to detect one GIM-1-producing P. aeruginosa isolate, whereas the high-strength TE disk detected this isolate.
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.
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.
ND, specificity could not be determined.