Table 3.
Minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) indices of chitosan–caffeic acid (CCA) in combination with antibiotics against antibiotic-resistant acne-related bacteria.
| Strains | Test Compound | MIC (μg/mL) | Median ∑FIC 1 | ∑FICmax 2 | ∑FICmin 3 | Minimum Concentration for Observing Synergy |
|---|---|---|---|---|---|---|
| P. acnes KCTC 3314 | CCA | 256 | 0.533 | 1.016 | 0.188 | 64.0 |
| Tetracycline | 32 | 4.0 | ||||
| P. acnes isolate 2874 | CCA | 256 | 0.502 | 1.004 | 0.375 | 64.0 |
| Tetracycline | 16 | 4.0 | ||||
| P. acnes KCTC 3314 | CCA | 256 | 0.502 | 1.004 | 0.188 | 32.0 |
| Erythromycin | 1024 | 64.0 | ||||
| P. acnes isolate 2874 | CCA | 256 | 0.502 | 1.016 | 0.313 | 64.0 |
| Erythromycin | 1024 | 128.0 | ||||
| Pseudomonas aeruginosa KCTC 1637 | CCA | 16 | 0.5 | 1.063 | 0.266 | 4.0 |
| Erythromycin | 16 | 0.5 | ||||
| P. acnes KCTC 3314 | CCA | 256 | 0.504 | 1.016 | 0.375 | 64.0 |
| Lincomycin | 1024 | 256.0 | ||||
| P. acnes isolate 2874 | CCA | 256 | 0.502 | 1.016 | 0.313 | 64.0 |
| Lincomycin | 1024 | 256.0 | ||||
| P. aeruginosa KCTC 1637 | CCA | 16 | 0.375 | 1.063 | 0.266 | 4.0 |
| Lincomycin | 64 | 16.0 |
1 ∑FIC, the sum of FICs; 2 ∑FICmax, the highest, ∑FIC; 3 ∑FICmin, the lowest ∑FIC. The FIC index indicated synergistic effect: <0.5, marked synergy; 0.5 to <1.0, weak synergy; 1.0, additive; >1.0 to <2.0, subadditive; 2.0, indifferent; >2.0, antagonistic.