Table 2. Target mutations identified in CHL- and FFC-resistant mutants.
| MIC (µg/mL)b | ||||||||||
| Strains a | CHL | CHL+PAβN | FFC | FFC+PAβN | Erythromicin | Azithromycin | Mutation in the 23S rRNA gene c | Change in protein L4 | Change in protein L22 | Selective Agents e |
| ATCC33560 | 4 | 4 | 2 | 2 | 1 | 0.25 | -d | - | - | NA |
| C1 | 32 | 32 | 16 | 16 | 8 | 1 | - | G74D | - | CHL |
| C2 | 64 | 32 | 32 | 16 | 8 | 1 | G2073A | G74D | - | CHL |
| C3 | 128 | 64 | 64 | 64 | 8 | 1 | G2073A | G74D | - | CHL |
| F1 | 8 | 4 | 16 | 8 | 2 | 0.5 | - | - | - | FFC |
| F2 | 16 | 8 | 32 | 32 | 8 | 1 | G2073A | - | - | FFC |
| F3 | 32 | 8 | 64 | 32 | 8 | 1 | G2073A | - | - | FFC |
| F4 | 64 | 16 | 128 | 64 | 8 | 1 | G2073A | - | - | FFC |
| F5 | 64 | 32 | 256 | 128 | 8 | 1 | G2073A | - | - | FFC |
a
C1-C3 were selected with CHL, while F1-F5 were selected with FFC.
b
Determined by the standard agar dilution method. ND, not determined.
c
The G2073A mutation was present in three copies of the domain V region of 23s rRNA gene.
d
no mutation detected.
e
CHL: Chloramphenicol; FFC: Florfenicol; NA: not applicable.