Table 2. Establishment of TRLU Thresholds to Discriminate between Inhibitory and Non-Inhibitory Antibiotics for A. baumannii (n = 30), P. aeruginosa (n = 30) and K. pneumoniae (n = 40).
| Antibiotics | No. of Specimens Inhibitory/Non-Inhibitory based on Viable Count Determination (%) | Area under the ROC curve (95% CI) a | Sensitivity and Specificity of Bioluminescence Assay w.r.t Viable Counts (%) a | Unweighted Accuracy of the Assay (%)a | Established TRLU values a | ||
|---|---|---|---|---|---|---|---|
| Inhibitory | Non-Inhibitory | Sensitivity | Specificity | ||||
| All Organisms (No. of isolates = 100) | |||||||
| All antibiotics (single and 2-drug combinations) | 716 (74.6) | 244 (25.4) | 0.95 (0.93–0.96) | 91.1 | 86.9 | 89.0 | 0.81 |
| A. baumannii (No. of isolates = 30) | |||||||
| All antibiotics (single and 2-drug combinations) | 118 (65.6) | 62 (34.4) | 0.92 (0.88–0.96) | 83.1 | 90.3 | 86.7 | 0.83 |
| Polymyxin B | 28 (93.3) | 2 (6.7) | - | - | - | - | - |
| Rifampicin | 3 (10.0) | 27 (90.0) | - | - | - | - | - |
| Tigecycline | 8 (26.7) | 22 (73.3) | - | - | - | - | - |
| Polymyxin B + rifampicin | 28 (93.3) | 2 (6.7) | 0.94 (0.90–0.99) | 90.0 | 93.3 | 91.7 | 0.49 |
| Polymyxin B + tigecycline | 29 (96.7) | 1 (3.33) | 0.94 (0.88–0.98) | 89.2 | 92.0 | 90.6 | 1.03 |
| Tigecycline + rifampicin | 22 (73.3) | 8 (26.7) | 0.80 (0.71–0.89) | 69.7 | 71.9 | 70.8 | 1.27 |
| P. aeruginosa (No. of isolates = 30) | |||||||
| All antibiotics (single and 2-drug combinations) | 146 (81.1) | 34 (18.8) | 0.92 (0.89–0.96) | 82.2 | 97.1 | 89.7 | 0.22 |
| Polymyxin B | 29 (96.7) | 1 (3.3) | - | - | - | - | - |
| Amikacin | 23 (76.7) | 7 (23.3) | - | - | - | - | - |
| Meropenem | 7 (23.3) | 23 (76.7) | - | - | - | - | - |
| Polymyxin B + amikacin | 30 (100) | 0 (0) | 0.98 (0.96–1.00) | 93.9 | 100 | 97.0 | 0.27 |
| Polymyxin B + meropenem | 30 (100) | 0 (0) | 0.92 (0.86–0.97) | 84.8 | 87.5 | 86.2 | 0.45 |
| Amikacin + meropenem | 27 (90.0) | 3 (10.0) | 0.89 (0.81–0.95) | 73.7 | 90.9 | 82.3 | 0.42 |
| K. pneumoniae (No. of isolates = 40) | |||||||
| All antibiotics (single and 2-drug combinations) | 452 (75.3) | 148 (24.7) | 0.96 (0.94–0.98) | 92.9 | 89.2 | 91.1 | 0.81 |
| Polymyxin B | 37 (92.5) | 3 (7.5) | - | - | - | - | - |
| Rifampicin | 0 (0) | 40 (100) | - | - | - | - | - |
| Tigecycline | 20 (50.0) | 20 (50.0) | - | - | - | - | - |
| Meropenem | 30 (75.0) | 10 (25.0) | - | - | - | - | - |
| Levofloxacin | 17 (42.5) | 23 (57.5) | - | - | - | - | - |
| Polymyxin B + rifampicin | 39 (97.5) | 1 (2.5) | 0.99 (0.99–1.00) | 100 | 97.7 | 98.9 | 1.23 |
| Polymyxin B + tigecycline | 37 (92.5) | 3 (7.5) | 0.95 (0.91–0.99) | 89.4 | 84.6 | 87.0 | 0.42 |
| Polymyxin B + meropenem | 39 (97.5) | 1 (2.5) | 0.98 (0.96–1.00) | 98.6 | 92.9 | 95.8 | 1.44 |
| Polymyxin B + levofloxacin | 40 (100) | 0 (0) | 0.99 (0.98–1.00) | 100 | 94.6 | 97.3 | 1.76 |
| Rifampicin + tigecycline | 35 (87.5) | 5 (12.5) | 0.92 (0.88–0.97) | 92.7 | 84.6 | 88.7 | 1.20 |
| Rifampicin + meropenem | 32 (80.0) | 8 (20.0) | 0.99 (0.98–1.00) | 96.8 | 96.6 | 96.7 | 1.26 |
| Rifampicin + levofloxacin | 17 (42.5) | 23 (57.5) | 1.00 (1.00–1.00) | 100 | 100 | 100 | 1.74 |
| Tigecycline + meropenem | 39 (97.5) | 1 (2.5) | 0.91 (0.79–0.95) | 87.6 | 80.6 | 84.1 | 0.50 |
| Tigecycline + levofloxacin | 36 (90.0) | 4 (10.0) | 0.89 (0.82–0.96) | 95.9 | 78.7 | 87.5 | 1.16 |
| Meropenem + levofloxacin | 34 (85.0) | 6 (15.0) | 0.96 (0.91–1.00) | 95.1 | 92.3 | 93.7 | 1.52 |
a For each antibiotic pair; results from the single drugs and 2-drug combinations were employed to generate the ROC curve and determine the sensitivity and specificity of the assay.