Haem is crucial for medium-dependent metronidazole resistance in clinical isolates of <i>Clostridioides difficile</i>
Ilse M. Boekhoud, Igor A. Sidorov, Sam Nooij, Céline Harmanus, Ingrid M. J. G. Bos-Sanders, Virginie Viprey, William Spittal, Emma Clark, Kerrie Davies, Jane Freeman, Ed J. Kuijper, Wiep Klaas Smits, Marc J. M. Bonten, Kerrie Davies, Ed J. Kuijper, Maja Rupnik, Sebastian Wingen-Heiman, Evelina Tacconelli, Tuba Wilken, Nicolla Petrosillo
Abstract
BACKGROUND: Until recently, metronidazole was the first-line treatment for Clostridioides difficile infection and it is still commonly used. Though resistance has been reported due to the plasmid pCD-METRO, this does not explain all cases. OBJECTIVES: To identify factors that contribute to plasmid-independent metronidazole resistance of C. difficile. METHODS: Here, we investigate resistance to metronidazole in a collection of clinical isolates of C. difficile using a combination of antimicrobial susceptibility testing on different solid agar media and WGS of selected isolates. RESULTS: We find that nearly all isolates demonstrate a haem-dependent increase in the MIC of metronidazole, which in some cases leads to isolates qualifying as resistant (MIC >2 mg/L). Moreover, we find an SNP in the haem-responsive gene hsmA, which defines a metronidazole-resistant lineage of PCR ribotype 010/MLST ST15 isolates that also includes pCD-METRO-containing strains. CONCLUSIONS: Our data demonstrate that haem is crucial for medium-dependent metronidazole resistance in C. difficile.