Background: The recent emergence of azithromycin-resistant (AZM-R) N. gonorrhoeae isolates that have coevolved decreased susceptibility to extended-spectrum cephalosporins has caused great concern. Here we investigated the prevalence of decreased susceptibility to ceftriaxone (CRO D ) in AZM-R isolates and genetically characterized AZM-R isolates in Guangzhou, China from 2009 to 2013. Methods: The minimum inhibitory concentration (MIC) of AZM and ceftriaxone was determined using an agar-dilution method. All AZM-R isolates were screened for mutations in 23S rRNA, mtrR and penA genes and genotyped using N. gonorrhoeae multi-antigen sequence typing (NG-MAST). Results: Of the 485 identified N. gonorrhoeae isolates, 445 (91.8%) were isolated from male urethritis subjects, and 77 (15.9%) were AZM-R (MIC≥1mg/L), including 33 (6.8%) with AZM low-level resistant (AZM-LLR, MIC=1mg/L) and 44 (9.1%) with AZM middle-level resistant (AZM-MLR, MIC≥2mg/L). Significantly more CRO D (MIC≥0.125mg/L) showed in AZM-MLR isolates (43.2%, 19/44) as compared with that in AZM-LLR isolates (18.2%, 6/33) (p<0.05). For the 23S rRNA, mtrR, penA or combined 23S rRNA/MtrR/penA mutations, no significant difference was found between AZM-LLR isolates and AZM-MLR isolates (P>0.05); similar results were detected between combined AZM-LLR/CRO D isolates and combined AZM-MLR/CRO D isolates (P>0.05). No mutation A2059G or AZM high-level resistant (AZM-HLR, MIC≥256mg/L) isolate was detected. Among 77 AZM-R isolates, 67 sequence types (STs) were identified by NG-MAST, of which 30 were novel. Most STs were represented by a single isolate. Conclusions: The AZM-R together CRO D isolates are now present in Guangzhou, China, which deserve continuous surveillance and the mechanism of concurrent resistance needs further study.
Liang, J. Y., Cao, W. L., Li, X. D., Bi, C., Yang, R. D., Liang, Y. H., … Zhang, X. B. (2016). Azithromycin-resistant Neisseria gonorrhoeae isolates in Guangzhou, China (2009-2013): Coevolution with decreased susceptibilities to ceftriaxone and genetic characteristics. BMC Infectious Diseases, 16(1). https://doi.org/10.1186/s12879-016-1469-3