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. 2025 Dec;16(1):2502554.
doi: 10.1080/21505594.2025.2502554. Epub 2025 May 9.

Differences in virulence and drug resistance between Clostridioides difficile ST37 and ST1 isolates

Zirou Ouyang  1 , Jing Yang  1 , Huimin Zhang  2 , Min Zhao  1 , Huimin Yang  1 , Jiafeng Zhao  1 , Yaxuan Yang  3 , Cuixin Qiang  1 , Zhirong Li  1 , Pu Qin  1 , Weigang Wang  1 , Yanan Niu  1 , Jianhong Zhao  1
Affiliations

Differences in virulence and drug resistance between Clostridioides difficile ST37 and ST1 isolates

Zirou Ouyang et al. Virulence. 2025 Dec.

Abstract

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.

Keywords: Clostridioides difficile; ST1; ST37; antibiotic resistance; virulence.

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Conflict of interest statement

No potential conflict of interest was reported by the author(s).

Figures

Figure 1.
Figure 1.
Distribution of orthologous genes in ST37 and ST1 strains. (a) Venn diagram showing the number of shared and unique genes for the ST37 and ST1 strains. (b) and (c) show the enrichment of cluster of orthologous groups of proteins (COG) annotation of unique genes in ST37 and ST1, respectively. Other groups represent genes not annotated in the COG database.
Figure 2.
Figure 2.
Comparative analysis of the PaLoc region of ST37 strains and R20291. The heat map below the PaLoc region corresponds to mutations in genes of the same color within the PaLoc region. The color changes from light to dark represent frameshift, stop gain, non-synonymous single nucleotide variants (SNV), and synonymous SNV, respectively. Numbers within the heat map represent the number of mutation sites.
Figure 3.
Figure 3.
Heat map of non-synonymous mutations of genes in ST37 and ST1 strains. (a) Heat map of non-synonymous mutations of virulence-related genes in ST37 strains. (b) Heat map of all genes with non-synonymous mutations in ST1 strains. Numbers within the heat map represent the number of mutation sites.
Figure 4.
Figure 4.
Comparison of pathogenesis-related phenotypes between ST37 and ST1 strains. (a) Comparison of TcdB production between ST37 and ST1 strains. (b) Comparison of the number of spores measured for five consecutive days. (c) Comparison of self-aggregation rates. (d) Comparison of biofilm formation capacity. (e) and (f) show comparison of swimming motility and surface motility ability measured for seven consecutive days, respectively. Error bars represent standard error of the mean. ns, no significance, *p < 0.05; **p < 0.01.
Figure 5.
Figure 5.
Comparison of antibiotic resistance rates between ST37 and ST1 strains.
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