TABLE 4.
Effect of heme catabolites on metronidazole MICs
| Strain (ribotype) | MIC (μg/ml)a |
|||||||
|---|---|---|---|---|---|---|---|---|
| BHI | Heme | Hb | BLV | BLB | PPIX | FeCl3 | FeSO4 | |
| 17/27 (RT001)b | 0.50 | 32 | 8 | 0.50 | 0.50 | 0.50 | 0.50 | 0.50 |
| 70/76 (RT027)b | 0.50 | 8 | 4 | 1 | 0.5 | 0.25 | 0.50 | 1 |
| CD196 (RT027)c | 0.25 | 0.25 | 0.50 | 0.25 | 0.25 | 0.5 | 0.50 | 0.25 |
| BAA-1875 (RT078)c | 0.25 | 0.25 | 0.25 | 0.50 | 0.50 | 0.12 | 0.25 | 0.50 |
a
MICs of metronidazole with heme or catabolites were determined on BHI agars. Results are based on three biological replicates. Only BHI medium with heme (hemin or Hb [hemoglobin]) supported detection of metronidazole-resistant C. difficile. BHI agars were supplemented with catabolites at 8 μM, equivalent to 5 μg/ml of hemin. BLV, biliverdin; BLB, bilirubin; PPIX, protoporphyrin IX; FeCl3, iron chloride; FeSO4, iron sulfate.
b
Metronidazole resistant.
c
Metronidazole susceptible.