Comparison of Microdilution Method with Agar Dilution Method for Antibiotic Susceptibility Test of Neisseria gonorrhoeae

Shao-Chun Chen,1,2,* Jing-Wei Liu,1,2,* Xing-Zhong Wu,3 Wen-Ling Cao,4 Feng Wang,5 Jin-Mei Huang,3 Yan Han,1,2 Xiao-Yu Zhu,1,2 Bang-Yong Zhu,6 Quan Gan,6 Xiao-Zheng Tang,7 Xing Shen,8 Xiao-Lin Qin,3 Yu-Qi Yu,3 He-Ping Zheng,3 Yue-Ping Yin1,2 1Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing, People’s Republic of China; 2National Center for STD Control, Chinese Center for Disease Control and Prevention, Nanjing, People’s Republic of China; 3Clinical Laboratory, Guangdong Provincial Dermatology Hospital, Guangzhou, Guangdong, People’s Republic of China; 4Clinical Laboratory, Guangzhou Dermatology Hospital, Guangzhou, Guangdong, People’s Republic of China; 5Shenzhen Center for Chronic Diseases Control, Shenzhen, Guangdong, People’s Republic of China; 6Clinical Laboratory, Guangxi Provincial Dermatology Hospital, Nanning, Guangxi, People’s Republic of China; 7Clinical Laboratory, Hainan Provincial Dermatology Hospital, Haikou, Hainan, People’s Republic of China; 8Zhuhai Center for Chronic Diseases Control, Zhuhai, Guangdong, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yue-Ping YinNational Center for STD Control,Chinese Center for Disease Control and Prevention, 12 Jiangwangmiao Street, Nanjing 210042, People’s Republic of ChinaTel +86-25-85478024Email yinyp@ncstdlc.orgHe-Ping ZhengGuangdong Provincial Dermatology Hospital, 2 Lujing Road, Guangzhou 510091, People’s Republic of ChinaEmail zhhpf@hotmail.comIntroduction: Antimicrobial resistance (AMR) of Neisseria gonorrhoeae (N. gonorrhoeae) becomes a grave public health problem in the world. A strengthened Antimicrobial Resistance Surveillance Program is needed to track the trend of AMR development. However, the lack of a proper antimicrobial susceptibility test (AST) method is a barrier to expand the AMR surveillance in China. Traditional agar dilution (AD) method is laborious and E-test strips have no approval license for clinical use. Herein, a Chinese group modified the microdilution (MD) method for clinical ASTs. The objective of this study is to compare the MD method with the AD method for N. gonorrhoeae AST.Materials and Methods: A total of 166 clinical isolates were tested for antimicrobial susceptibility of ceftriaxone, spectinomycin, azithromycin, ciprofloxacin, tetracycline, and penicillin using MD and AD method simultaneously. Results of MD method were read manually or automatically. Rates of essential agreement (EA), category agreement (CA), minor error, and very major error were compared.Results: The total EAs (compared with results read manually) of penicillin, tetracycline, ciprofloxacin, spectinomycin, ceftriaxone, and azithromycin were 90.4%, 97.0%, 85.5%, 100.0%, 94%, and 72.3%; and CAs were 82.5%, 94.0%, 100%, 100%, 95.2%, and 94%, respectively.Conclusion: We conclude that the MD method might be an alternative for clinical AST of N. gonorrhoeae in China. In particular, MD method has the potency of accurate differentiation of isolates resistant to ceftriaxone or azithromycin, which were empirically recommended for gonococcal treatment, but its quality remained suboptimal, and further improvement is needed for clinical use.Keywords: Neisseria gonorrhoeae, antimicrobial susceptibility test