Antimicrobial resistance, genetic resistance determinants for ceftriaxone and molecular epidemiology of Neisseria gonorrhoeae isolates in Nanjing, China

Antimicrobial resistance (AMR) in Neisseria gonorrhoeae is a major problem worldwide. This study investigated the AMR, genetic ceftriaxone resistance determinants and molecular epidemiology of N. gonorrhoeae in Nanjing, China. N. gonorrhoeae isolates were collected in 2007 (naEuroS=aEuroS198) and 2012 (naEuroS=aEuroS80). The susceptibility to ceftriaxone, spectinomycin, ciprofloxacin and tetracycline was determined using an agar-dilution method. The ceftriaxone resistance determinants penA, mtrR and penB were examined using sequencing. N. gonorrhoeae multi-antigen sequence typing (NG-MAST) was performed for molecular epidemiology. All isolates were resistant to ciprofloxacin, 42.4% produced beta-lactamase and 34.9% showed high-level resistance to tetracycline (MIC a parts per thousand yen16 mg/L). In total, 5.4% of isolates were resistant to ceftriaxone; however, all of these isolates were obtained in 2007 and the susceptibility to ceftriaxone appeared to have increased. All isolates were susceptible to spectinomycin. No penA mosaic alleles were found. Non-mosaic penA alleles with A501T and G542S alterations, an H105Y alteration in mtrR and an A102D/N alteration in porB1b were statistically associated with decreased susceptibility or resistance to ceftriaxone. The most prevalent NG-MAST sequence types (STs) were ST568 (naEuroS=aEuroS13), ST270 (naEuroS=aEuroS9) and ST421 (naEuroS=aEuroS7). ST270 was the most common ST in isolates with decreased susceptibility or resistance to ceftriaxone. Ceftriaxone, ideally 500 mg and together with azithromycin (1-2 g), should be recommended for treatment of gonorrhoea in Nanjing, China. However, N. gonorrhoeae strains with resistance to ceftriaxone have been found in Nanjing. NG-MAST and ceftriaxone resistance determinant analysis can be valuable to supplement the antimicrobial resistance surveillance in China, which needs to be further strengthened.