Increasing Resistance to Azithromycin in Neisseria gonorrhoeae in Eastern Chinese Cities: Resistance Mechanisms and Genetic Diversity among Isolates from Nanjing

Abstract

Azithromycin resistance (AZM-R) of Neisseria gonorrhoeae is emerging as a clinical and public health challenge. We determined molecular characteristics of recent AZM-R Nanjing gonococcal isolates and tracked the emergence of AZM-R isolates in eastern Chinese cities in recent years. A total of 384 N. gonorrhoeae isolates from Nanjing collected from 2013 to 2014 were tested for susceptibility to AZM and six additional antibiotics; all AZM-R strains were characterized genetically for resistance determinants by sequencing and were genotyped using N. gonorrhoeae multiantigen sequence typing (NG-MAST). Among the 384 isolates, 124 (32.3%) were AZM-R. High-level resistance (MIC, ≥256 mg/liter) was present in 10.4% (40/384) of isolates, all of which possessed the A2143G mutation in all four 23S rRNA alleles. Low- to mid-level resistance (MIC, 1 to 64 mg/liter) was present in 21.9% (84/384) of isolates, 59.5% of which possessed the C2599T mutation in all four 23S rRNA alleles. The 124 AZM-R isolates were distributed in 71 different NG-MAST sequence types (STs). ST1866 was the most prevalent type in high-level AZM-R (HL-AZM-R) isolates (45% [18/40]). This study, together with previous reports, revealed that the prevalence of AZM-R in N. gonorrhoeae isolates in certain eastern Chinese cities has risen >4-fold (7% to 32%) from 2008 to 2014. The principal mechanisms of AZM resistance in recent Nanjing isolates were A2143G mutations (high-level resistance) and C2599T mutations (low- to mid-level resistance) in the 23S rRNA alleles. Characterization of NG-MAST STs and phylogenetic analysis indicated the genetic diversity of N. gonorrhoeae in Nanjing; however, ST1866 was the dominant genotype associated with HL-AZM-R isolates.

Emergence of Neisseria gonorrhoeae Strains Harboring a Novel Combination of Azithromycin-Attenuating Mutations

“…In recent years, many countries have observed an increase in the prevalence of reduced susceptibility to azithromycin in N. gonorrhoeae. The percentage of isolates displaying an elevated MIC to azithromycin ranged from 4.7% to 32% in 2014 to 2017 (3,(6)(7)(8)(9)(10). Most of the isolates with elevated azithromycin MICs can be associated with mutations in either the 23S rRNA gene or the mtr locus (15).…”

“…In the United States, the percentage of isolates with reduced cephalosporin susceptibility declined after 2012; however, the number and percentage of gonococcal isolates with reduced susceptibility to azithromycin have steadily increased since then (11). The increase in the number of N. gonorrhoeae isolates displaying elevated MICs to azithromycin is typically associated with the accumulation of genetic mutations in the multiple transferable resistance (mtr) locus or in the 23S rRNA gene (10,(12)(13)(14).…”

Transcriptome Analysis ofNeisseria gonorrhoeaeDuring Natural Infection Reveals Differential Expression of Antibiotic Resistance Determinants Between Men and Women

“…As there is little doubt about the intrinsic tissue, cellular and molecular differences that define these host environments, it is reasonable to assume that the gonococcus will adapt to these environmental differences during infection (65). Building on our previous results on the gonococcal transcriptome profile during infection in women (37), we extended our analysis to specimens from infected men. In the present study, we not only report a distinct gonococcal transcriptome profile in vivo as compared to in vitro in infected men, but also, for the first time, describe a comparison of N. gonorrhoeae gene expression during infection in the male and female genital tract.…”

“…data was performed using the Rockhopper program, aligning the reads to the NCBI genome sequence of N. gonorrhoeae strain FA1090, and then reporting RNA-seq. data in reads per kilobase per million (RPKM) (37). The cut-off for gene expression was set at an RPKM value of at least 10.…”

“…Previous work from our group using a gene specific microarray and qRT-PCR analysis demonstrated that a subset of gonococcal iron-regulated genes were expressed during human mucosal infection in men and women (34, 35). Recently, we also examined the complete N. gonorrhoeae transcriptome using cervico-vaginal lavage specimens of infected women attending an STI clinic in China where antibiotic resistant N. gonorrhoeae is prevalent (36, 37). We reported that a large portion of the gonococcal genome is expressed and regulated during infection (38).…”