Differences in virulence and drug resistance between <i>Clostridioides difficile</i> ST37 and ST1 isolates

One of the most common hospital-acquired infections is caused by toxigenic Clostridioides difficile. Although C. difficile ST37 only produces a functional toxin B, it causes disease as severe as that caused by hypervirulent ST1. We aim to compare the differences in virulence and drug resistance between ST37 and ST1 isolates. We conducted whole-genome sequencing on ST37 and ST1 isolates, analyzing their type-specific genes, and the distribution and mutation of genes related to virulence and antibiotic resistance. We compared the in vitro virulence-related phenotypes of ST37 and ST1 isolates, including: TcdB concentration, number of spores formed, aggregation rate, biofilm formation, swimming diameter in semi-solid medium, motility diameter on the surface of solid medium, and their resistance to 14 CDI-related antibiotics. We detected 4 ST37-specific genes related to adherence, including lytC, cbpA, CD3246, and srtB. We detected 97 virulence-related genes in ST37 isolates that exhibit genomic differences compared to ST1. ST37 isolates showed increased aggregation, biofilm formation, and surface motility compared to ST1 in vitro. Chloramphenicol resistance gene catQ and tetracycline resistance gene tetM are present in ST37 but absent in ST1 strains. The resistance rates of ST37 to chloramphenicol and tetracycline were 45.4% and 81.8%, respectively, whereas ST1 isolates were sensitive to both antibiotics. ST1 was more resistant to rifaximin than ST37. ST37 isolates showed stronger aggregation, biofilm formation and surface motility, and had higher resistance rates to chloramphenicol and tetracycline. ST1 isolates showed stronger ability to produce toxin and sporulation, and was highly resistant to rifaximin.