Table 3. Prospective Validation of the Established TRLU Thresholds using prospectively collected strains of A. baumannii (n = 15), P. aeruginosa (n = 15) and K. pneumoniae (n = 20).
| Antibiotics | No. of Single Drug and 2-drug combinations Inhibitory/Non-Inhibitory based on Viable Count Determination (%) | Sensitivity and Specificity of the Established TRLU Thresholds a | Unweighted Accuracy of the Established TRLU Thresholds b | ||
|---|---|---|---|---|---|
| Inhibitory | Non-Inhibitory | Sensitivity | Specificity | ||
| All Organisms (No. of isolates = 50) | |||||
| All antibiotics (single and 2-drug combinations) | 331 (69.0) | 149 (31.0) | 90.8 | 92.9 | 91.2 |
| A. baumannii (No. of isolates = 15) | |||||
| All antibiotics (single and 2-drug combinations) | 56 (62.2) | 34 (37.8) | 75.0 | 85.3 | 80.2 |
| Polymyxin B | 11 (73.3) | 4 (26.7) | - | - | - |
| Rifampicin | 3 (20.0) | 12 (80.0) | - | - | - |
| Tigecycline | 5 (33.3) | 10 (66.7) | - | - | - |
| Polymyxin B + rifampicin | 14 (93.3) | 1 (6.7) | 89.2 | 88.2 | 88.7 |
| Polymyxin B + tigecycline | 12 (80.0) | 3 (20.0) | 85.7 | 82.3 | 84.0 |
| Tigecycline + rifampicin | 11 (73.3) | 4 (26.7) | 68.4 | 76.9 | 72.7 |
| P. aeruginosa (No. of isolates = 15) | |||||
| All antibiotics (single and 2-drug combinations) | 76 (84.4) | 14 (15.6) | 86.8 | 100 | 93.4 |
| Polymyxin B | 14 (93.3) | 1 (6.7) | - | - | - |
| Amikacin | 12 (80.0) | 3 (20.0) | - | - | - |
| Meropenem | 5 (33.3) | 10 (66.7) | - | - | - |
| Polymyxin B + amikacin | 15 (100) | 0 (0) | 95.1 | 100 | 97.6 |
| Polymyxin B + meropenem | 15 (100) | 0 (0) | 85.3 | 100 | 92.7 |
| Amikacin + meropenem | 15 (100) | 0 (0) | 78.5 | 100 | 89.3 |
| K. pneumoniae (No. of isolates = 20) | |||||
| All antibiotics (single and 2-drug combinations) | 199 (66.3) | 101 (33.7) | 94.0 | 91.1 | 92.6 |
| Polymyxin B | 14 (70.0) | 6 (30.0) | - | - | - |
| Rifampicin | 0 (0) | 20 (100) | - | - | - |
| Tigecycline | 12 (60.0) | 8 (40.0) | - | - | - |
| Meropenem | 14 (70.0) | 6 (30.0) | - | - | - |
| Levofloxacin | 7 (35.0) | 13 (65.0) | - | - | - |
| Polymyxin B + rifampicin | 15 (75.0) | 5 (25.0) | 96.6 | 100 | 98.3 |
| Polymyxin B + tigecycline | 17 (85.0) | 3 (15.0) | 79.1 | 94.1 | 86.6 |
| Polymyxin B + meropenem | 17 (85.0) | 3 (15.0) | 100 | 86.7 | 93.4 |
| Polymyxin B + levofloxacin | 19 (95.0) | 1 (5.0) | 95.0 | 85.0 | 90.0 |
| Rifampicin + tigecycline | 13 (65.0) | 7 (35.0) | 92.7 | 84.6 | 88.7 |
| Rifampicin + meropenem | 14 (70.0) | 6 (30.0) | 100 | 96.9 | 98.5 |
| Rifampicin + levofloxacin | 8 (40.0) | 12 (60.0) | 93.3 | 97.8 | 95.6 |
| Tigecycline + meropenem | 17 (85.0) | 3 (15.0) | 90.7 | 94.1 | 92.4 |
| Tigecycline + levofloxacin | 18 (90.0) | 2 (10.0) | 97.2 | 95.6 | 96.4 |
| Meropenem + levofloxacin | 14 (70.0) | 6 (30.0) | 97.1 | 84.0 | 90.6 |
a For each antibiotic pair, the observations, sensitivity, specificity and unweighted accuracy of the bioluminescence assay were determined collectively for the 2-drug combination as well as the respective single drugs.
b The established TRLU values employed corresponded to the TRLU values shown in Table 1.