Table 3.
FIC index of combinations among silver nanoparticles and antibiotics against clinical and reference strains.
| Bacterial Strains | FIC Index | |||
|---|---|---|---|---|
| AgNPs + AMK | AgNPs + AMP | |||
| Gram-positive | ||||
| Staphylococcus aureus (ATCC 25923) | 1.06 | (AD) | 1.03 | (AD) |
| Enterococcus faecium | 0.53 | (PS) | 0.56 | (PS) |
| Staphylococcus aureus | 0.63 | (PS) | 1.25 | (AD) |
| Gram-negative | ||||
| Escherichia coli (ATCC 25922) | 0.31 | (S) | 1.50 | (AD) |
| Acinetobacter baumannii | 0.28 | (S) | 0.31 | (S) |
| Enterobacter cloacae | 0.75 | (PS) | 1.25 | (AD) |
| Escherichia coli (501) ** | 0.56 | (PS) | 0.56 | (PS) |
| Escherichia coli (508) ** | 0.31 | (S) | 0.56 | (PS) |
| Escherichia coli (515) ** | 0.75 | (PS) | 0.56 | (PS) |
| Klebsiella pneumoniae | 0.75 | (PS) | 0.53 | (PS) |
| Morganella morganii | 0.75 | (PS) | 0.56 | (PS) |
| Pseudomonas aeruginosa | 0.63 | (PS) | 0.53 | (PS) |
FIC: Fractional Inhibitory Concentration. AMK: Amikacin. AMP: Ampicillin. ATCC: American Type Culture Collection. The FIC index was interpreted as follows: FIC ≤ 0.5, Synergy (S); 0.5 ≤ FIC < 1, Partial Synergy (PS); FIC = 1, Additive (AD); 2 ≤ FIC < 4, Indifferent (I); FIC > 4, Antagonism (AN) [32,33]. ** The numbers in parentheses indicate that E. coli corresponds to a different clinical sample.