Table 1. Number and percentage of positive isolates in dilution and disk method with imipenem or meropenem for metallo-β-lactamase (MBL) positive strains (true positive), carbapenem-hydrolyzing class D carbapenemases (CHDL) producing strains (false positive) and carbapenemase negative strains. Reduction of minimum inhibitory concentrations (MICs) and increase of the inhibition zone in the presence of EDTA is shown (range and median).
| Type of carbapenemase | Number of positive strains /number of strains tested* n (%) | Range of imipenem MIC (mg/L) reduction (X-fold) † | Number of positive strains /number of strains tested n (%) | Range of meropenem MIC (mg/L) reduction (X-fold) † | Number of positive strains /number of strains tested‡ n (%) | Range of inhibition zone enlargement (mm) around the imipenem disk (median) | Number of positive strains /number of strains tested‡ n (%) | Range of inhibition zone enlargement (mm) around the meropenem disk (median) |
|---|---|---|---|---|---|---|---|---|
| VIM+OXA-23 | 11/11 (100%) | 16->64 (32) | 11/11 (100%) | 16-256 (64) | 11/11 (100%) | 8-15 (13) | 11/11 (100%) | 12-18 (16) |
| OXA-23 | 16/16 (100%) | 8-32 (16) | 16/16 (100%) | 8-64 (16) | 16/16 (100%) | 8-16 (11) | 16/16 (100%) | 9-17 (13) |
| OXA-24/40 | 74/74 (100%) | 4->128 (16) | 74/74 (100%) | 8-256 (16) | 74/74 (100%) | 8-17 (14) | 74/74 (100%) | 8-17 (15) |
| OXA-58 | 15/22 (68%) | 4->128 (48) | 15/22 (68%) | 4-512 (32) | 17/22 (77%) | 4-18 (10.5) | 16/22 (73%) | 5-19 (13) |
| Carbapenemase negative | 1/49 (2%) | 0-4 (2) | 1/49 (2%) | 0-8 (4) | 4/49 (8%) | 0-10 (5) | 5/49 (10%) | 0-8 (5) |
*broth microdilution method with imipenem as indicator; †EDTA and 1,10-phenanthroline; ‡combined disk test with imipenem or meropenem disk as indicator