Chromosome and Plasmid Features of Two ST37 Clostridioides difficile Strains Isolated in China Reveal Distinct Multidrug Resistance and Virulence Determinants

Clostridioides difficile ST37 is an emerging and prevalent multilocus sequence type and represents a lineage of clinical significance. This study aimed to characterize two epidemic C. difficile ST37 strains, CD161 and CDT4. CD161 acquires a chromosome and two distinct plasmids, pCD161-L, sharing high similarity with Clostridium phage, and pCD161-S, while CDT4 has a chromosome and a plasmid pCDT4 identical to pCD161-S. In the chromosome of both strains, three CdISt1-like elements and a skinCd element, which might influence sporulation, were identified. The multidrug resistance of the strains was due to the mutation in 23S rDNA, gyrA, and gyrB genes and the acquisition of ermB, ant6-Ia, aac6'-aph2'', and tetM genes. In addition, a distinct pathogenicity locus (PaLoc) with truncated tcdA gene represents the genetic feature of ST37 strains. To our knowledge, this is the first complete genome, both chromosomes and plasmids, of epidemic C. difficile ST37 strains in China.