High-level cefixime- and ceftriaxone-resistant Neisseria gonorrhoeae in France: novel penA mosaic allele in a successful international clone causes treatment failure

Abstract

Recently, the first Neisseria gonorrhoeae strain (H041) highly resistant to the expanded-spectrum cephalosporins (ESCs) ceftriaxone and cefixime, which are the last remaining options for first-line gonorrhea treatment, was isolated in Japan. Here, we confirm and characterize a second strain (F89) with high-level cefixime and ceftriaxone resistance which was isolated in France and most likely caused a treatment failure with cefixime. F89 was examined using six species-confirmatory tests, antibiograms (33 antimicrobials), porB sequencing, N. gonorrhoeae multiantigen sequence typing (NG-MAST), multilocus sequence typing (MLST), and sequencing of known gonococcal resistance determinants (penA, mtrR, penB, ponA, and pilQ). F89 was assigned to MLST sequence type 1901 (ST1901) and NG-MAST ST1407, which is a successful gonococcal clone that has spread globally. F89 has high-level resistance to cefixime (MIC = 4 μg/ml) and ceftriaxone (MIC = 1 to 2 μg/ml) and resistance to most other antimicrobials examined. A novel penA mosaic allele (penA-CI), which was penA-XXXIV with an additional A501P alteration in penicillin-binding protein 2, was the primary determinant for high-level ESC resistance, as determined by transformation into a set of recipient strains. N. gonorrhoeae appears to be emerging as a superbug, and in certain circumstances and settings, gonorrhea may become untreatable. Investigations of the biological fitness and enhanced understanding and monitoring of the ESC-resistant clones and their international transmission are required. Enhanced disease control activities, antimicrobial resistance control and surveillance worldwide, and public health response plans for global (and national) perspectives are also crucial. Nevertheless, new treatment strategies and/or drugs and, ideally, a vaccine are essential to develop for efficacious gonorrhea management.

Fig 1

Alignment of PBP 2 sequences from strains of Neisseria gonorrhoeae with different penA alleles. M32091, wild-type PBP 2; XXXIV, penA mosaic allele previously described (27, 33); CI, penA mosaic allele of F89; XXVI (27, 36) and XXX (27, 51), the only previously reported true penA mosaic alleles containing an A501 alteration (27); C, penA mosaic allele of H041, which is the first high-level ceftriaxone-resistant strain found in Japan (27); and XIII and XVIII, previously described nonmosaic penA alleles that contain A501V (most prevalent) and A501T alterations (27, 51). Identical amino acids are designated by a dot, and alterations from the wild-type sequence are shown with a single capital letter. The three active-site motifs are marked by dashed boxes, while the location of amino acid Ala501 (position 502 in the alignment due to the D345 insertion) is marked with a solid box.

Fig 2

MICs of a set of recipient strains transformed with the full-length penA allele (penA-CI) from the high-level cefixime- and ceftriaxone-resistant Neisseria gonorrhoeae strain F89 (donor). The MICs of cefixime and ceftriaxone and the number and type of resistance determinants (e.g., mtrR, penB, and ponA) in the recipient strains varied. The MICs of cefixime (A) and ceftriaxone (B) were determined using the Etest method, and the values shown are the means of three transformation experiments (the bars give only whole-MIC steps), with the exact mean MICs in parentheses. The ratios of the MICs of the transformant to the recipient strain (T/R) are indicated.