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Background   Corynebacterium striatum  was confirmed to be an important opportunistic pathogen, which could lead to multiple-site infections and presented high prevalence of multidrug resistance, particularly to quinolone antibiotics. This study aimed to investigate the mechanism underlying resistance to quinolones and the epidemiological features of 410 quinolone-resistant  C. striatum  clinical strains isolated from three tertiary hospitals in China.    Methods  A total of 410  C. striatum  clinical strains were isolated from different clinical samples of patients admitted to three tertiary teaching hospitals in China. Antibiotic susceptibility testing was performed using the microdilution broth method and pulsed-field gel electrophoresis (PFGE) was used for genotyping. Gene sequencing was used to identify possible mutations in the quinolone resistance-determining regions (QRDRs) of  gyrA .    Results  In total, 410  C. striatum  isolates were sensitive to vancomycin, linezolid, and daptomycin but resistant to ciprofloxacin. Depending on the antibiotic susceptibility testing results of 12 antimicrobial agents, the 410  C. striatum  strains were classified into 12 resistant biotypes; of these, the three biotypes R1, R2, and R3 were dominant and accounted for 47.3% (194/410), 21.0% (86/410), and 23.2% (95/410) of the resistant biotypes, respectively. Mutations in the QRDRs of gyrA  were detected in all quinolone-resistant  C. striatum  isolates, and 97.3% of the isolates (399/410) showed double mutations in codons 87 and 91 of the QRDRs of  gyrA . Ser-87 to Phe-87 and Asp-91 to Ala-91 double mutation in  C. striatum  was the most prevalent and accounted for 72.2% (296/410) of all mutations. Four new mutations in  gyrA  were identified in this study; these included Ser-87 to Tyr-87 and Asp-91 to Ala-91 (double mutation, 101 isolates); Ser-87 to Val-87 and Asp-91 toGly-91 (double mutation, one isolate); Ser-87 to Val-87 and Asp-91 to Ala-91 (double mutation, one isolate); and Ser-87 to Ile-87 (single mutation, one isolate). The minimum inhibitory concentration of ciprofloxacin for isolates with double (96.5%; 385/399) and single (72.7%; 8/11) mutations was high (≥ 32 µg/mL). Based on the PFGE typing results, 101 randomly selected  C. striatum  strains were classified into 50 genotypes (T01-T50), including the three multidrug-resistant epidemic clones T02, T06, and T28; these accounted for 14.9% (15/101), 5.9% (6/101), and 11.9% (12/101) of all genotypes, respectively. The multidrug-resistant T02 clone was identified in hospitals A and C and persisted from 2016 to 2018. Three outbreaks resulting from the T02, T06, and T28 clones were observed among intensive care unit (ICU) patients in hospital C between April and May 2019.    Conclusions  Quinolone-resistant  C. striatum  isolates showed a high prevalence of multidrug resistance. Point mutations in the QRDRs of  gyrA  conferred quinolone resistance to  C. striatum , and several mutations in  gyrA  were newly found in this study. The great clonal diversity, high-level quinolone resistance and increased prevalence among patients susceptible to  C. striatum  isolates deserve more attention in the future. Moreover, more thorough investigation of the relationship between quinolone exposure and resistance evolution in  C. striatum  is necessary.

annals of clinical microbiology and antimicrobials

Wide spread and diversity of mutation in the gyrA gene of quinolone-resistant Corynebacterium striatum strains isolated from three tertiary hospitals in China