Characterization of a stable, metronidazole-resistant Clostridium difficile clinical isolate.
BACKGROUND
Clostridium difficile are gram-positive, spore forming anaerobic bacteria that are the leading cause of healthcare-associated diarrhea, usually associated with antibiotic usage. Metronidazole is currently the first-line treatment for mild to moderate C. difficile diarrhea however recurrence occurs at rates of 15-35%. There are few reports of C. difficile metronidazole resistance in the literature, and when observed, the phenotype has been transient and lost after storage or exposure of the bacteria to freeze/thaw cycles. Owing to the unstable nature of the resistance phenotype in the laboratory, clinical significance and understanding of the resistance mechanisms is lacking.


RESULTS
Genotypic and phenotypic characterization was performed on a metronidazole resistant clinical isolate of C. difficile. Whole-genome sequencing was used to identify potential genetic contributions to the phenotypic variation observed with molecular and bacteriological techniques. Phenotypic observations of the metronidazole resistant strain revealed aberrant growth in broth and elongated cell morphology relative to a metronidazole-susceptible, wild type NAP1 strain. Comparative genomic analysis revealed single nucleotide polymorphism (SNP) level variation within genes affecting core metabolic pathways such as electron transport, iron utilization and energy production.


CONCLUSIONS
This is the first characterization of stable, metronidazole resistance in a C. difficile isolate. The study provides an in-depth genomic and phenotypic analysis of this strain and provides a foundation for future studies to elucidate mechanisms conferring metronidazole resistance in C. difficile that have not been previously described.
National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba, Canada.
Tarah
T
Lynch
Patrick
P
Chong
Jason
J
Zhang
Romeo
R
Hizon
Tim
T
Du
Morag R
MR
Graham
Daniel R
DR
Beniac
Timothy F
TF
Booth
Pamela
P
Kibsey
Mark
M
Miller
Denise
D
Gravel
Michael R
MR
Mulvey
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D016360:Clostridioides difficile / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification* / Q000648:ultrastructure; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D018432:Drug Resistance, Multiple / Q000187:drug effects; D023281:Genomics; D006801:Humans; D008795:Metronidazole / Q000494:pharmacology*; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide
D000900:Anti-Bacterial Agents; D008795:Metronidazole