Table 2. Stability and activity spectrum of suicin 3908.
| Treatment | Indicator strain | Inhibitory activity |
|---|---|---|
| 45°C / 15 min | S. suis MGGUS3 | + |
| 70°C / 15 min | S. suis MGGUS3 | + |
| 100°C / 15 min | S. suis MGGUS3 | + |
| 121°C / 15 min | S. suis MGGUS3 | + |
| 4°C / 7 d | S. suis MGGUS3 | + |
| 25°C / 7 d | S. suis MGGUS3 | + |
| pH 2 / 15 min | S. suis MGGUS3 | + |
| pH 11 / 15 min | S. suis MGGUS3 | + |
| Trypsin / 60 min | S. suis MGGUS3 | + |
| Chymotrypsin / 60 min | S. suis MGGUS3 | + |
| Proteinase K / 60 min | S. suis MGGUS3 | + |
| None | S. aureus ATCC 25923 | - |
| None | S. hyicus ATCC 11249 | + |
| None | A. pleuropneumoniae 81–750 | - |
| None | A. suis JG-2 | - |
| None | B. bronchiseptica ATCC 19395 | - |
| None | E. coli P82–862 | - |
| None | H. parasuis 99–9048-B | - |
| None | P. multocida ATCC 12948 | - |
The MIC of suicin 3908 against S. suis MGGUS3 was determined and was compared to that of commercial nisin A to assess its relative antibacterial activity. Suicin 3908 had a MIC of 0.47 µg/mL while that of nisin A was 0.156 µg/mL. We used the checkerboard technique to determine whether suicin 3908 in combination with antibiotics had a synergistic or additive effect against S. suis MGGUS3. Suicin 3908 in association with penicillin G or amoxicillin gave a FICI of 1, which indicates an additive effect.