TABLE 3.
Synergy of the peptides with ciprofloxacin, carbenicillin, and nalidixic acid against P. aeruginosa strains
| Peptide | FIC indexa
|
|||
|---|---|---|---|---|
| Ciprofloxacin vs H744 nalB | Carbenicillin vs H547 | Nalidixic acid vs H374 nalA | Nalidixic acid vs H744 nalB | |
| CPα1 | 0.5 | 0.75 | 0.38 | 0.38 |
| CPα2 | 0.69 | 1 | 0.5 | 0.63 |
| CPα3 | 0.63 | 0.75 | 0.5 | 0.5 |
| CM1 | B | B | —b | — |
| CM2 | B | B | — | — |
| CM3 | — | 0.75 | — | — |
| CM4 | 0.75 | B | — | — |
| CM5 | 0.75 | 0.38 | — | — |
| CM6 | A | B | — | — |
| CM7 | 0.63 | B | — | — |
| CP201 | 0.49 | 0.53 | 0.42 | 0.75 |
| CP202 | 0.49 | 0.63 | 0.5 | 0.66 |
| CP203 | 0.78 | B | 0.38 | 0.44 |
| CP204 | 0.26 | B | — | — |
| CP205 | 0.52 | B | 0.31 | 0.42 |
| CP206 | 0.63 | 0.53 | 0.42 | 0.33 |
| CP207 | 0.65 | B | 0.5 | 0.5 |
| CP208 | 0.6 | B | 0.38 | 0.58 |
| CP209 | 0.52 | B | 0.31 | 0.58 |
| CP210 | 0.52 | B | 0.31 | 0.58 |
To calculate the FIC index, the following formula was used: FIC index = [A]/(MIC A + [B])/MIC B, where [A] was the concentration of drug A in a well that represented the lowest inhibitory concentration in its row, MIC A was the MIC of drug A alone, [B] was the concentration of drug B in a well that represented the lowest inhibitory concentration in its row, and MIC B was the MIC of drug B alone. An FIC index of 0.5 or less is taken to imply synergy. An FIC index of 0.5 to 0.9 is marginal synergy. An FIC index of 1.0 implies that the two agents are additive. An FIC index of 2.0 implies antagonism. A and B imply that the MIC of agent A (the peptide) or B (the conventional antibiotic) did not change at any peptide or antibiotic concentration, respectively. The FIC indexes shown are averages of two or three determinations.
—, not done.