The characteristics of Clostridium difficile ST81, a new PCR ribotype of toxin A- B+ strain with high-level fluoroquinolones resistance and higher sporulation ability than ST37/PCR ribotype 017.

Antibiotic exposure, Clostridium difficile toxins, and spore formation are key factors involved in the pathogenesis of Clostridium difficile infection (CDI). A high incidence of CDI due to toxin A- B+ strains, which were classified into two genotypes (ST81 and ST37) by multilocus sequence typing, was identified in Beijing Friendship Hospital in 2016-2017. ST81 was the most prevalent type, accounting for 81.25% of toxin A- B+ strains. ST81 corresponded to a novel PCR ribotype, PKI-017, with one less band than ST37/ribotype 017 in PCR ribotyping. All ST81 strains showed a high level of ciprofloxacin resistance (MICs ≥ 64 μg mL-1) and moxifloxacin resistance (MICs ≥ 128 μg mL-1) with the amino acid substitutions Thr82 to Ile in GyrA and Ser416 to Ala in GyrB. There was either no mutation or only the single amino acid mutation Thr82 to Ile in the GyrA subunit of ST37/ribotype 017 strains, which had lower MICs of ciprofloxacin (4-64 μg mL-1) and moxifloxacin (4-16 μg mL-1). In addition, ST81 strains exhibited higher spore formation ability than ST37/ribotype 017 strains. Overall, our results indicated that ST81 strains had unique characteristics distinguishable from ST37 strains and emphasized the importance of ongoing surveillance for this new genotype.