Antibiotic resistant mechanism and epidemiological characteristics of azithromycin-resistant Neisseria gonorrhoeae strains in Shenzhen / 中华微生物学和免疫学杂志

ABSTRACT

Objective To investigate the prevalence, molecular mechanism and genetic characteristics of azithromycin-resistant Neisseria gonorrhoeae (N.gonorrhoeae) strains isolated in Shenzhen.Methods N.gonorrhoeae strains were collected in Shenzhen from 2011 to 2015.Agar dilution method and E-test were used to detect the minimum inhibitory concentrations (MIC) of these strains to azithromycin.All azithromycin-resistant (AZM-R) strains (MIC≥2 μg/ml) and some azithromycin-sensitive strains (MIC≤0.25 μg/ml) which were randomly selected as the control group were screened for mutations in 23S rRNA, mtrR and erm genes and genotyped by using N.gonorrhoeae multi-antigen sequence typing (NG-MAST).Results A total of 788 N.gonorrhoeae strains were collected, 148 (18.8%) of which were AZM-R strains (MIC≥1 μg/ml).Eighteen out of 21 high-level AZM-R (AZM-HLR) strains had A2143G mutations in the four copies of the 23S rRNA gene.Twelve out of 29 middle-level AZM-R (AZ-MLR) strains had missense mutations, among which C2611T mutations in the four copies of the 23S rRNA were detected in 10 strains.Incidence of G45D/Y105H mutation in AZM-HLR strains was higher than that in AZM-MLR (χ2=12.702, P=0.000) or AZ-S (χ2=4.462, P=0.035) strains according to the analysis of the promoter and coding region of mtrR gene.PCR analysis revealed that only one strain carried ermB gene (MIC=2 μg/ml).The 788 N.gonorrhoeae strains were typed into 81 sequence types (STs) by NG-MAST, most of which were represented by one strain only.STs of ST3356 and ST1866 that were identified in the AZ-R strains in the current study had been noted in a previous report of emerging AZM-R N.gonorrhoeae strains in Nanjing, Chongqing and Guangzhou.Neighbor-joining (NJ) phylogenetic tree showed that the resistant strains did not form a separate cluster.Conclusion Currently, it is not suitable to use azithromycin as a monotherapy for gonorrhea in Shenzhen.Mutations of A2059G and C2611T in 23S rRNA of N.gonorrhoeae were respectively responsible for high-level and middle-level resistance to azithromycin.Repeated emergence of ST1866 and ST3356 will help us monitor and analyze the epidemiological characteristics of N.gonorrhoeae strains resistant to azithromycin in Shenzhen.