Ceftriaxone susceptibility testing and multi-antigen sequence typing of Neisseria gonorrhoeae strains isolated in 2007 and 2012 from Nanjing, China

Abstract

Objective To test the ceftriaxone susceptibility of Neisseria gonorrhoeae (NG) isolates from Nanjing city,and to assess their genotypes by using the NG multi-antigen sequence typing (NG-MAST) method.Methods A total of 204 NG strains isolated in 2007 and 81 in 2012 from Nanjing city were included in this study.The minimum inhibitory concentration (MIC) of ceftriaxone was determined for these strains using an agar dilution method.DNA was extracted by the Qiagen commercial kit from these strains followed by NG-MAST.Results All the isolates were susceptible to ceftriaxone (MIC,≤ 0.25 μg/ml).The MIC of ceftriaxone was ≥ 0.06 μg/ml for 63.2％ of all the NG strains,70.6％ of those isolated in 2007 and 44.4％ of those in 2012,and ≥ 0.125 μg/ml for 31.6 ％ of all the NG strains,39.7％ of those isolated in 2007,11.1％ of those in 2012.Totally,166 genotypes were identified among the 285 isolates,of which,73 had been reported,and 93 were previously unreported.The most prevalent genotype was ST568 (n =13) in NG strains isolated in 2007,followed by ST270 (n =9),ST421 (n =7),ST2288 (n =5),ST1731 (n =4),ST1766 (n =4),ST1866 (n =4),ST1870 (n =4),while ST2318 (n =5),ST1053 (n =4),ST5990 (n =4),ST8726 (n =4) were the common genotypes in 2012.Those isolates with identical or similar genotypes tended to display similar MICs for ceftriaxone.Conclusions The prevalent genotypes of NG are markedly different between 2007 and 2012 in Nanjing region,and there is a strong association between the genotypes and ceftriaxone susceptibility of NG.NG-MAST results may serve as a genetic marker in the surveillance of antibiotic susceptibility in NG. Key words: Neisseria gonorrhoeae; Drug resistance; Ceftriaxone