TABLE 3.
S. aureus FBEC index values.
| MBEC for 2CP (alone) (μg/ml) | MBEC for 2CP (combined) (μg/ml) | MBEC for antibiotic (alone) (μg/ml) | MBEC for antibiotic (combined) (μg/ml) | FBEC | Interpretation | |
| S. aureus | ||||||
| Tobramycin | 1,000 | 31.25 | 2.5 | 1.25 | 0.531 | Additive |
| Tetracycline | 1,000 | 125 | 1.25 | 0.625 | 0.625 | Additive |
| Levofloxacin | 1,000 | 250 | 1 | 0.25 | 0.5 | Synergistic |
| MBEC for C2DA (alone) (μg/ml) | MBEC for C2DA (combined) (μg/ml) | MBEC for antibiotic (alone) (μg/ml) | MBEC for antibiotic (combined) (μg/ml) | FBEC | Interpretation | |
| Tobramycin | 1,000 | 125 | 2.5 | 1.25 | 0.625 | Additive |
| Tetracycline | 1,000 | 500 | 1 | 0.25 | 0.75 | Additive |
| Levofloxacin | 1,000 | 125 | 1 | 0.25 | 0.375 | Synergistic |
| MBEC for T2DA (alone) (μg/ml) | MBEC for T2DA (combined) (μg/ml) | MBEC for antibiotic (alone) (μg/ml) | MBEC for antibiotic (combined) (μg/ml) | FBEC | Interpretation | |
| Tobramycin | 1,000 | 125 | 2.5 | 1.25 | 0.625 | Additive |
| Tetracycline | 1,000 | 500 | 1 | 0.25 | 0.75 | Additive |
| Levofloxacin | 1,000 | 500 | 1 | 0.25 | 0.75 | Additive |
Minimum biofilm eradication concentration (MBEC) for 2CP, C2DA, and T2DA against S. aureus biofilm when treated alone or combined with tobramycin, tetracycline, or levofloxacin. MBEC of each antibiotic against S. aureus alone is also included. These values were used in Equation 2 to determine the fractional inhibitory concentration index for each fatty acid/antibiotic combination. FBEC index values less than or equal to 0.5 indicate synergy, values between 0.5 and 1 indicate additivity, values between 1 and 2 indicate indifference, and values above 2 indicate antagonism.