Tetracycline-resistant Neisseria gonorrhoeae strains isolated in a Grade III hospital in eastern China: molecular characteristics and genetic diversity
Objective 
To analyze the genotypes of Neisseria gonorrhoeae (N.gonorrhoeae) epidemic strains in Wenzhou, eastern China, and to study the mechanism of tetracycline resistance in these strains. 
 
 
Methods 
A total of 77 N. gonorrhoeae strains were isolated from patients with gonorrhea. Antimicrobial susceptibility of these strains to penicillin, tetracycline, ciprofloxacin, spectinomycin, ceftriaxone and azithromycin was analyzed using E-test. PCR and DNA sequencing were used to detect the genes associated with tetracycline resistance, such as Tet-M, mtrR promoter region and mtrR coding region. N. gonorrhoeae multi-antigen sequence typing (NG-MAST) and multilocus sequence typing (MLST) were used to determine the molecular characteristics of all clinical isolates and tetracycline-resistant isolates, respectively. 
 
 
Results 
Among the 77 N. gonorrhoeae isolates, 74 (96.10%), 27 (35.06%) , 70 (90.91%) and 15 (19.48%) were resistant to penicillin, tetracycline, ciprofloxacin and azithromycin, respectively. All tested isolates were susceptible to spectinomycin and ceftriaxone. Nineteen isolates were resistant to tetracycline and all of them carried Tet-M gene. Among them, 17 had one deletion mutation of base A in mtrR promoter region and three had G45D mutation in mtrR coding region. NG-MAST classified the 19 tetracycline-resistant isolates into 11 different sequence types (ST). ST14781, ST1766 and ST1866 each accounted for 15.79% (three strains). Two ST (10.52%, 2/19) found in the present study had not been reported previously in the NG-MAST database. MLST showed the 19 tetracycline-resistant isolates belonged to 12 different STs, in which ST10899 accounted for 26.32% (five strains) and ST1600 accounted for 15.79% (three strains). 
 
 
Conclusions 
Mutations in mtrR promoter region and carrying Tet-M gene were associated with tetracycline resistance in N. gonorrhoeae. Clinical strains isolated in Wenzhou showed considerable molecular diversity. Measures should be implemented to monitor the spread of NG-MAST ST1766 and MLST ST1600 N. gonorrhoeae clones with high resistance to tetracycline in Wenzhou. 
 
 
Key words: 
Neisseria gonorrhoeae; Resistance rate; Tetracycline; NG-MAST; MLST