Markedly Increasing Antibiotic Resistance and Dual Treatment of Neisseria gonorrhoeae Isolates in Guangdong, China, from 2013 to 2020

Abstract

The emergence of multidrug resistance in Neisseria gonorrhoeae is concerning, especially the cooccurrence of azithromycin resistance and decreased susceptibility to extended-spectrum cephalosporin. This study aimed to confirm the antibiotic resistance trends and provide a solution for N. gonorrhoeae treatment in Guangdong, China. A total of 5,808 strains were collected for assessment of antibiotic MICs. High resistance to penicillin (53.80 to 82%), tetracycline (88.30 to 100%), ciprofloxacin (96 to 99.8%), cefixime (6.81 to 46%), and azithromycin (8.60 to 20.03%) was observed. Remarkably, spectinomycin and ceftriaxone seemed to be the effective choices, with resistance rates of 0 to 7.63% and 2.00 to 16.18%, respectively. Moreover, the rates of azithromycin resistance combined with decreased susceptibility to ceftriaxone and cefixime reached 9.28% and 8.64%, respectively. Furthermore, genotyping identified NG-STAR-ST501, NG-MAST-ST2268, and MLST-ST7363 as the sequence types among representative multidrug-resistant isolates. Evolutionary analysis showed that FC428-related clones have spread to Guangdong, China, which might be a cause of the rapid increase in extended-spectrum cephalosporin resistance currently. Among these strains, the prevalence of N. gonorrhoeae was extremely high, and single-dose ceftriaxone treatment might be a challenge in the future. To partially relieve the treatment pressure, a susceptibility test for susceptibility to azithromycin plus extended-spectrum cephalosporin dual therapy was performed. The results showed that all the representative isolates could be effectively killed with the coadministration of less than 1 mg/liter azithromycin and 0.125 mg/liter extended-spectrum cephalosporin, with a synergistic effect according to a fractional inhibitory concentration (FIC) of <0.5. In conclusion, dual therapy might be a powerful measure to treat refractory N. gonorrhoeae in the context of increasing antibiotic resistance in Guangdong, China.

Keywords: FC428; N. gonorrhoeae; dual therapy; genotyping; resistance.

FIG 1

Antimicrobial resistance trends of N. gonorrhoeae isolates from Guangdong, China. (A) Percentage of gonococcal isolates resistant to PEN, TET, CIP, SPT, and AZM and with decreased susceptibility to CRO and CFM. (B to H) Proportion of N. gonorrhoeae isolates with different MICs (mg/liter) for PEN (B), TET (C), CIP (D), SPT (E), CRO (F), CFM (G), and AZM (H) (n = 5,808 isolates). (I) Percentage of gonococcal isolates with both AZM^r and CRO^d (solid circle) or CFM^d (blank circle). PEN, penicillin; TET, tetracycline; CIP, ciprofloxacin; SPT, spectinomycin; AZM, azithromycin; CFM, cefixime; CRO, ceftriaxone; AZM^r, azithromycin resistance; CRO^d, decreased susceptibility to ceftriaxone; CFM^d, decreased susceptibility to cefixime.

FIG 2

Genotyping and evolutionary analysis of MDR N. gonorrhoeae. (A) The number of each sequence type was counted according to NG-STAR. (B) The number of each penA allele carrying a nonmosaic or mosaic gene. Amino acid alterations within the mosaic penA allele related to decreased susceptibility to ESC are cited in red. (C and D) The number of each sequence type was counted according to NG-MAST and MLST analyses. The colored histogram indicates ≥2 ST. NG-STAR, N. gonorrhoeae sequence typing for antimicrobial resistance; NG-MAST, N. gonorrhoeae multiantigen sequence typing; MLST, multilocus sequence typing; NA, new allele. (E) Multilocus phylogeny of 79 MDR isolates and two identified FC428 clones (FC428 and GC249). The phylogenetic tree was constructed based on MLST alleles. Bootstrap values higher than 85% are indicated. Red font indicates the original FC428 strain found in Japan, and purple font indicates the FC428-related clone GC249 identified in China. MLST, multilocus sequence typing; MDR, multidrug resistant.

FIG 3

Interaction between AZM and ESC results in growth inhibition. The fractional inhibitory concentration (FIC) index for each strain treated with drug combinations is shown for AZM plus CFM (A) and AZM plus CRO (B). The red font indicates the specific FIC index. AZM, azithromycin; ESC, extended-spectrum cephalosporin; CFM, cefixime; CRO, ceftriaxone.