Table 3.
Comparison of the effect of fluoroquinolone resistance selection on the MIC of various antimicrobial agents and ethidium bromide. Ethidium bromide concentrations in the plates were 0, 2, 4, 5, 6, 8, and 10 µg/mL.
| C. perfringens strains | MIC (µg/mL), as shown by Etest for antimicrobial agents or agar dilution for ethidium bromide | |||||||
|---|---|---|---|---|---|---|---|---|
| Erythromycin | Amoxicillin | Ceftriaxone | Gentamicin | Chloramphenicol | Cefoxitin | Metronidazole | Ethidium bromide | |
| 3626 | ||||||||
| W | 2 | 0.1 | 1 | 128 | 3 | 1 | 1.5 | 6 |
| NR | 1.5 | 0.19∗a | 0.016 | 48 | 8* | 0.25 | 3* | 10∗∗b |
| CR | 0.5 | 0.1 | 4* | 12 | 2 | 1 | 1.5 | 10** |
| GR | 1 | 0.25* | 0.016 | 64 | 6* | 2* | 3* | 5 |
| 13124 | ||||||||
| W | 2 | 0.25 | 64 | 512 | 8 | 4 | 3 | 4 |
| NR | 0.75 | 0.125 | 16 | 64 | 3 | 1.5 | 1.5 | 2 |
| CR | 1.5 | 0.75* | 32 | 128 | 8 | 2 | 4* | 4 |
| GR | 1 | 2* | 12 | 256 | 3 | 4 | 1.5 | 2 |
| NCTR | ||||||||
| W | 2 | 0.13 | 4 | 128 | 4 | 0.38 | 1.5 | 2 |
| NR | 0.75 | 0.2 | 0.016 | 128 | 3 | 0.75* | 0.75 | 10** |
| CR | 1 | 0.2 | 3 | 48 | 4 | 0.5 | 1 | 10** |
| GR | 0.75 | 0.1 | 1 | 32 | 3 | 1* | 1.5 | 10** |
| VPI | ||||||||
| W | 1.5 | 0.25 | 16 | 384 | 3 | 0.75 | 3 | 6 |
| NR | 3 | 0.38 | 16 | 64 | 4 | 1.5* | 3 | 8** |
| CR | 1.5 | 1.5* | 16 | 256 | 3 | 3* | 2 | 10** |
| GR | 0.75 | 0.5* | 64* | 256 | 6* | 2* | 3 | 8** |
aThe ∗ indicates that fluoroquinolone resistance selection resulted in a decrease in susceptibility; W, NR, CR, and GR refer to wild type, norfloxacin-resistant, ciprofloxacin-resistant, and gatifloxacin-resistant, respectively. b∗∗Resistant strains grew on the plates containing 10 µg/mL of ethidium bromide, so the MIC of the ethidium bromide was greater than 10 µg/mL for these strains.