Objective:This work aims to investigate the virulence features, spore formation and the resistance mechanisms of major sequence types (STs) of clinical Clostridium difficile isolates from nosocomial infectious diarrhea. Methods:Clostridium difficile isolates were prospectively collected from 816 loose stool samples of in patients with antibiotic associated diarrhea at the Beijing Friendship Hospital of Capital Medical University from September 2017 to September 2019. The main ST types ST81 (26 strains), ST8 (15 strains) and ST42 (14 strains) of C. difficile were used as experimental strains. The polymerase chain reaction (PCR) and enzyme-linked immunoassay (ELISA) were performed to detect toxin genes and toxin production of different C. difficile ST types, respectively. The count of the colony forming units (CFU) of the strains as conducted by using the brain-heart infusion (BHI) agar plates. The antimicrobial resistance patterns of the strains to eleven kinds of antibiotics were determined by agar dilution method. The antimicrobial resistance genes: gyrA, gyrB and ermB were amplified and sequenced from the stains. Mutations in the resistance genes were analyzed by sequencing. Measure data was compared by Kruskal Wallis Test, differences in the resistance rates in three group were compared using Fisher exact test. Results:ST81 strains were identified as the tcdA-tcdB+/ cdtA-cdtB-toxin type, ST8 and ST42 strains belonged to tcdA+tcdB+/ cdtA-cdtB-toxin type. The toxin production of ST42 strains (41.9) were higher than ST8 (2.4) and ST81 groups (0.83) (all P<0.001). The number of spore quantities of ST81, ST8 and ST42 strains were 494×10 5CFU/ml, 160×10 5CFU/ml and 166×10 5CFU/ml, respectively. The spore quantities of ST81 strains were much higher than that of ST81 and ST42 strains (all P<0.001). From the in vitro susceptibility test, 100% (26/26) ST81 strains were featured as multi-drug resistant (MDR), and they were resistant to moxifloxacin, ceftriaxone, erythromycin and clindamycin. The resistance rates of ST8 strain to moxifloxacin, erythromycin and clindamycin were 9/15, 11/15 and 11/15, respectively. ST81 strains had higher resistance rates to moxifloxacin, clindamycin and erythromycin, compared to ST8 strains ( P=0.001, P=0.005 and P=0.005). All ST42 strains were susceptible to ceftriaxone and 3/14 ST42 strains were resistant to moxifloxacin. ST81 strains had higher resistance rates to ceftriaxone and moxifloxacin than the ST42 strains (both P<0.001). The positive rate of ermB in ST81 strains (100%, 26/26) were higher the ST8 strains (11/15) ( P<0.005). Amino acid mutation analysis showed that ST81and ST8 stains had one amino acid substitution in both GyrA and GyrB, but the amino acid substitutions were different in GyrB between two ST types. ST81 strains had two point-mutations: Thr82 replaced by Ile in GyrA, and Asp426 replaced by Val in GyrB. ST8 strains had point-mutation: Thr82 replaced by Ile in GyrA; Asp426 replaced by Asn in GyrB. For ST42 strains, Thr82 was replaced by Ile in GyrA. Conclusions:ST81 and ST42 strains were MDR. ST81 had higher spore ability, whereas ST42 strains had more virulence. ST81 strains and most of ST8 strains had high level of fluoroquinolones resistance. It is important to supervise persistently these three ST genotypes to prevent further dissemination.