Molecular Characteristics and the Effect of Mutations in Different Sites of the rplD Gene Among Clinical Isolates of Azithromycin Resistance Neisseria gonorrhoeae in Eastern China

Background: The emergence of resistance to azithromycin complicates the treatment of Neisseria gonorrhoeae, the causative agent of gonorrhea. Objectives: The main objective of this study was to investigate the impact of mutations in different sites of the rplD gene on azithromycin resistance (AZM-R) and the molecular characteristics of N. gonorrhoeae. This study aimed to provide evidence for drug resistance and transmission. Methods: A total of 37 isolates of N. gonorrhoeae were collected within January 2018 to December 2020. These isolates were obtained from urine, semen, or vaginal secretions of different patients. Azithromycin resistance was assessed, and genes associated with AZM-R, namely rplD, and rplV, were analyzed using polymerase chain reaction (PCR) and deoxyribonucleic acid (DNA) sequencing. All clinical isolates were characterized through multi-locus sequence typing (MLST). Results: The study comprised 21 azithromycin-resistant N. gonorrhoeae isolates, with two of them demonstrating high resistance, indicated by a minimum inhibitory concentration (MIC) greater than 256 µg/mL. Additionally, 16 sensitive isolates were included in the study. Ten isolates were observed to have rplD point mutations, including mutations such as G70D, G70S, G68D, and A43T. No mutations were detected in rplV. The rate of point mutations in rplD was significantly different between the azithromycin-sensitive (AZM-S) group and the AZM-R group (P < 0.05). Among the 37 isolates studied, 12 distinct MLST types were identified and further grouped into four different MLST goeBURST groups. The two isolates with high-level AZM-R were ST1901 and ST1588, respectively. Conclusions: The clinical isolates of N. gonorrhoeae from Wenzhou, Eastern China, exhibit significant genetic diversity and a relatively high prevalence of AZM-R. Mutations in the rplD gene were identified, which reduced susceptibility to macrolides and were significantly associated with increased AZM-R.