Is Neisseria gonorrhoeae initiating a future era of untreatable gonorrhea?: detailed characterization of the first strain with high-level resistance to ceftriaxone

Abstract

Recently, the first Neisseria gonorrhoeae strain (H041) that is highly resistant to the extended-spectrum cephalosporin (ESC) ceftriaxone, the last remaining option for empirical first-line treatment, was isolated. We performed a detailed characterization of H041, phenotypically and genetically, to confirm the finding, examine its antimicrobial resistance (AMR), and elucidate the resistance mechanisms. H041 was examined using seven species-confirmatory tests, antibiograms (30 antimicrobials), porB sequencing, N. gonorrhoeae multiantigen sequence typing (NG-MAST), multilocus sequence typing (MLST), and sequencing of ESC resistance determinants (penA, mtrR, penB, ponA, and pilQ). Transformation, using appropriate recipient strains, was performed to confirm the ESC resistance determinants. H041 was assigned to serovar Bpyust, MLST sequence type (ST) ST7363, and the new NG-MAST ST4220. H041 proved highly resistant to ceftriaxone (2 to 4 μg/ml, which is 4- to 8-fold higher than any previously described isolate) and all other cephalosporins, as well as most other antimicrobials tested. A new penA mosaic allele caused the ceftriaxone resistance. In conclusion, N. gonorrhoeae has now shown its ability to also develop ceftriaxone resistance. Although the biological fitness of ceftriaxone resistance in N. gonorrhoeae remains unknown, N. gonorrhoeae may soon become a true superbug, causing untreatable gonorrhea. A reduction in the global gonorrhea burden by enhanced disease control activities, combined with wider strategies for general AMR control and enhanced understanding of the mechanisms of emergence and spread of AMR, which need to be monitored globally, and public health response plans for global (and national) perspectives are important. Ultimately, the development of new drugs for efficacious gonorrhea treatment is necessary.

Fig. 1.

Phylogenetic tree describing the evolutionary relationships of full-length porB gene sequences of the high-level ceftriaxone-resistant Neisseria gonorrhoeae strain H041 compared with those of previously published N. gonorrhoeae penA mosaic isolates (11). The 2008 WHO K reference strain (41), containing a penA mosaic allele X and cultured in Japan in 2001, was used to root the tree. The N. gonorrhoeae multiantigen sequence typing (NG-MAST) sequence type (ST) and number of isolates are indicated.

Fig. 2.

A schematic figure describing all reported penicillin-binding protein 2 (PBP2) amino acid sequences in Neisseria gonorrhoeae, which are aligned to the wild-type PBP2 sequence M32091. All amino acid alterations in the different PBP2 sequences are illustrated with a single capital letter. The amino acids in PBP2 of H041 differing from PBP2 mosaic X (n = 12) are indicated (#). The four amino acid residues in the highly ceftriaxone-resistant N. gonorrhoeae strain H041 not previously observed in any Neisseria species and which explained the ceftriaxone resistance are shown by white letters on a blue ground. The amino acid residue marked with an asterisk has previously been found in N. meningitidis (unpublished) and N. flavescens (GenBank accession number M26645).

Fig. 3.

Transformation of the full-length penA allele (penA_H041) from the high-level ceftriaxone-resistant Neisseria gonorrhoeae strain H041 (Donor) into N. gonorrhoeae strains (Recipients) with different ceftriaxone MICs and genetic resistance determinants affecting the susceptibility to ceftriaxone. The ceftriaxone MICs using the Etest method (shown as mean results of three repeated experiments) of the donor strain, recipient strains (R), and transformants (T) and the MIC ratio (T/R) are given. The breakpoint for ceftriaxone resistance is according to reference .