Table 2.
MICs (μg/mL) and FIC indices (FICIs) of Tet and d-Tet in combination with four antibiotics against 10 clinical MRSA strains of SCCmec III type.
| Agent a | Range | 50%b | 90% | |
|---|---|---|---|---|
| Tet/AMP | MIC (μg/mL) | 64–128/32–128 | 64/64 | 128/64 |
| Rd% c | 0–50/0–50 | 0/0 | 0/0 | |
| FICI (E d) | 1.5(I)–2(I) | 2(I) | 2(I) | |
| d-Tet/AMP | MIC (μg/mL) | 64–128/32–128 | 64/64 | 128/128 |
| Rd% | 0–50/0–0 | 0/0 | 0/0 | |
| FICI (E) | 1.5(I)–2(I) | 2(I) | 2(I) | |
| Tet/AZM | MIC (μg/mL) | 64–128/2000–4000 | 64/4000 | 128/4000 |
| Rd% | 0–50/0–0 | 0/0 | 0/0 | |
| FICI (E) | 2(I)–2(I) | 2(I) | 2(I) | |
| d-Tet/AZM | MIC (μg/mL) | 64–128/2000–4000 | 64/4000 | 128/4000 |
| Rd% | 0–0/0–0 | 0/0 | 0/0 | |
| FICI (E) | 2(I)–2(I) | 2(I) | 2(I) | |
| Tet/CFZ | MIC (μg/mL) | 8–32/16–64 | 8/32 | 32/64 |
| Rd% | 75–94/75–88 | 88/75 | 75/75 | |
| FICI (E) | 0.25(S)–0.5(S) | 0.375(S) | 0.5(S) | |
| d-Tet/CFZ | MIC (μg/mL) | 8–64/16–64 | 16/32 | 32/64 |
| Rd% | 50–88/75–94 | 75/75 | 75/75 | |
| FICI (E) | 0.188(S)–0.625(A) | 0.5(A) | 0.5(A) | |
| Tet/LEV | MIC (μg/mL) | 64–128/8–32 | 64/16 | 128/16 |
| Rd% | 0–50/0–50 | 0/0 | 0/0 | |
| FICI (E) | 1.5(I)–2(I) | 1.5(I) | 2(I) | |
| d-Tet/LEV | MIC (μg/mL) | 32–128/8–32 | 64/16 | 128/16 |
| Rd% | 0–50/0–50 | 0/0 | 0/0 | |
| FICI (E) | 1.5(I)–2(I) | 1.5(I) | 2(I) | |
a Tet: tetrandine; d-Tet: demethyltetrandrine; AMP: ampicillin; CFZ: cefazolin; LEV: levofloxacin; AZM: azithromycin; b 50% means MIC50, concentration of inhibition against 50% of MRSA strains; 90% means MIC90, concentration of inhibition against 90% of MRSA strains; c Rd%: % of MIC reduced, Rd% = (MICalone − MICcombined) × 100 / MICalone. Values are expressed as those of alkaloids/antibiotics; d E: Effect; A: additivity (0.5 < FICI ≤ 1); I: Indifference (1 < FICI ≤ 2); S: Synergy (FICI ≤ 0.5).