TABLE 3.
Determination of presence of MBL producers among CAZ-resistant but IPM-susceptible isolates of P. aeruginosa and Acinetobacter spp.a
| Isolates (no. tested) | blaVIM-2 or blaIMP-1 status (no. of isolates) | No. of isolates positive byc:
|
No. of isolates with the following CAZ/IPM result:
|
||||||
|---|---|---|---|---|---|---|---|---|---|
| Hodge testb | IPM-EDTA (1,900 μg) DDSTb | CAZ-MPA (3 μl) DDSTb | R/R | I or R/I or R | I or R/I or S | S/R | S/S | ||
| Consecutive | |||||||||
| P. aeruginosa (100) | Positive (5) | 4 (1) | 5 | 5 | 3 | 2 | 0 | 0 | 0 |
| Negative (95) | 1 | 1 | 1 | 4 | 3 | 13 | 10 | 65 | |
| Acinetobacter spp. (99) | Positive (2) | 1 (1) | 1 (1) | 1 (1) | 1 | 1 | 0 | 0 | 0 |
| Negative (97) | 0 | 0 | 0 | 15 | 0 | 56 | 2 | 24 | |
| CAZ-nonsusceptible | |||||||||
| P. aeruginosa (168) | Positive (38) | 33 (5) | 36 (2) | 32 (6) | 36 | 2 | 0 | NA | NA |
| Negative (130) | 4 | 10 | 8 | 102 | 18 | 10 | NA | NA | |
| Acinetobacter spp. (73) | Positive (4) | 3 (1) | 3 (1) | 3 (1) | 4 | 0 | 0 | NA | NA |
| Negative (69) | 5 | 3 | 0 | 46 | 17 | 6 | NA | NA | |
| Total (440) | Positive (49) | 41 (8) | 45 (4) | 41 (8) | 44 | 5 | 0 | 0 | 0 |
| Negative (391) | 10 | 14 | 9 | 167 | 38 | 85 | 12 | 89 | |
Abbreviations: R, resistant; I, intermediate; S, susceptible; NA, not applicable.
Numbers of isolates that were positive by a repeat Hodge test with Zn2+-added IPM disks, and numbers of isolates that were DDST positive by repeated tests, are given in parentheses. All of the false-positive Hodge test and DDST results were equivocal.
Sensitivities and specificities, excluding repeated tests, were as follows: for the Hodge test, 83.7 and 97.4%, respectively; for the IPM-EDTA DDST, 91.8 and 96.4%, respectively; and for the CAZ-MPA DDST, 83.7 and 97.7%, respectively. The differences in sensitivity and specificity between the two DDSTs were statistically significant (P < 0.01 by the chi-square test).