Jingjia Zhang,1,2,* Xue Li,1,* Xinmiao Jia,3,* Yun Li,4 Bo Zheng,4 Yunsong Yu,5 Fupin Hu,6 Ziyong Sun,7 Zhongju Chen,7 Ge Zhang,1 Wei Kang,1 Tong Wang,1 Jin Li,1 Haotian Gao,1 Qiaolian Yi,1 Wei Yu,1,8 Xiaobing Chu,1,8 Yingchun Xu,1 Qiwen Yang1,9 

1Department of Clinical Laboratory, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China; 2Clinical Biobank, Biomedical Engineering Facility of National Infrastructures for Translational Medicine, Chinese Academy of Medical Sciences, Peking Union Medical College Hospital, Beijing, Peoples Republic of China; 3Department of Medical Research Center, State Key Laboratory of Complex Severe & Rare Diseases, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China; 4Institute of Clinical Pharmacology, Peking University, Beijing, People’s Republic of China; 5Department of Clinical Infectious Diseases, Zhejiang Provincial People’s Hospital, Hangzhou, People’s Republic of China; 6Huashan Hospital of Fudan University, Shanghai, People’s Republic of China; 7Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China; 8Graduate School, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, People’s Republic of China; 9Key Laboratory of Pathogen Infection Prevention and control (Peking Union Medical College), Ministry of Education, Beijing, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Qiwen Yang, Department of Clinical Laboratory, Peking Union Medical College Hospital, Email yangqiwen81@vip.163.com

Objective: To establish the epidemiological cut-off values (ECOFFs) of sitafloxacin against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Acinetobacter baumannii, Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, and Streptococcus pneumoniae.
Methods: We collected 2264 clinical isolates from five different labs located in four cities in China. The minimum inhibitory concentrations (MICs) and inhibition zone diameters of sitafloxacin for all isolates were determined by using the broth microdilution method (BMD) and the disk diffusion method according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. MIC ECOFFs were determined using ECOFFinder software, with the 99% calculated ECOFF selected as the initial value. Zone diameter ECOFFs were determined via the visual estimation method. Whole-genome sequencing was performed on E. coli strains exhibiting overlapping MICs between wild-type (WT) and non-wild-type (NWT) groups to analyze resistance mechanisms.
Results: Sitafloxacin MICs ranged from 0.002 to 64 mg/L, while inhibition zone diameters ranged from 6 to 45 mm across the nine species. MIC ECOFFs were determined as 0.032, 0.064, 0.125, 0.5, 0.064, 0.125, 0.5, 0.25, and 0.125 mg/L for E. coli, K. pneumoniae, P. mirabilis (tentative ECOFF), P. aeruginosa, A. baumannii, S. aureus, E. faecalis, E. faecium, and S. pneumoniae, respectively. Except for S. pneumoniae, MICs of the other eight species showed a high correlation with zone diameters (|r| > 0.8, P < 0.0001). Consequently, the zone diameter ECOFFs were established as 26, 25, 24, 24, 25, 26, 21, and 22 for E. coli, K. pneumoniae, P. mirabilis, P. aeruginosa, A. baumannii, S. aureus, E. faecalis, and E. faecium, respectively.
Conclusion: We established MIC and zone diameter ECOFFs for sitafloxacin against the nine species listed above. The MIC ECOFF for P. mirabilis was classified as tentative. For S. pneumoniae, the correlation between zone diameters and MICs was insufficient to establish a zone diameter ECOFF.

Keywords: sitafloxacin, ECOFF, MIC, zone diameter, BMD, disk diffusion