Increasing Incidence of High-Level Tetracycline-Resistant Neisseria gonorrhoeae due to Clonal Spread and Foreign Import

Abstract

Purpose: The detection of high-level tetracycline-resistant strains of Neisseria gonorrhoeae (TRNG) can make important epidemiological contributions that are relevant to controlling infections from this pathogen. In this study, we aimed to determine the incidence of TRNG isolates over time and also to investigate the characteristics and genetic epidemiology of these TRNG isolates in Korea.

Materials and methods: The antimicrobial susceptibilities of 601 isolates of N. gonorrhoeae from 2004 to 2011 were tested by standard Clinical and Laboratory Standards Institute methods. To determine the molecular epidemiological relatedness, N. gonorrhoeae multi-antigen sequence typing was performed.

Results: The incidence of TRNG increased from 2% in 2004 to 21% in 2011. The minimum inhibitory concentration distributions of ceftriaxone and susceptibility of ciprofloxacin in TRNG were different from non-TRNG and varied according to the year of isolation. Most of the TRNG isolates collected from 2004 to 2007 exhibited genetic relatedness, with sequence type (ST) 1798 being the most common. From 2008 to 2011, the STs of the isolates became more variable and introduction of genetically unrelated TRNG were noted.

Conclusion: The increased incidence of TRNG strains until 2007 appears to be due, at least in part, to clonal spread. However, we propose that the emergence of various STs since 2008 could be associated with foreign import.

Keywords: NG-MAST; Neisseria gonorrhoeae; antimicrobial resistance; epidemiology; tetracycline.

Fig. 1. Summary of the number and percentage of TRNG isolates obtained in Korea by year. TRNG, high-level tetracycline-resistant Neisseria gonorrhoeae.

Fig. 2. Evolutionary relationships of por gene of TRNG and non-TRNG isolated in Korea during 2006 (A) and 2010–2011 (B). The phylogenetic tree was drawn by MEGA6 software using the Neighbor-Joining method. Allele numbers belonging to TRNG are marked with a red dot. TRNG, high-level tetracycline-resistnat Neisseria gonorhoeae; MEGA6, Molecular Evolutionary Genetics Analysis version 6.

Fig. 3. Phylogenetic tree of the tbpB alleles harbored by various TRNG isolates obtained in Korea from 2004 to 2011 made by MEGA6 software using the Neighbor-Joining method. TRNG, high-level tetracycline-resistnat Neisseria gonorhoeae; MEGA6, Molecular Evolutionary Genetics Analysis version 6.