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Sir,

Antimicrobial resistance in Neisseria gonorrhoeae is a major public health challenge, with gonococci developing resistance to multiple classes of antibiotics. There are now increasing numbers of reports of gonococci with reduced susceptibility to extended-spectrum cephalosporins (ESCs), and documented treatment failures of genital tract gonorrhoea using oral ESCs in Japan and Hong Kong.1,2 Reduced susceptibility to ESCs in N. gonorrhoeae has been associated with alterations in the gonococcal penicillin-binding protein 2 (PBP2), including mosaic PBP2 (considered a key alteration of interest) and PBP2 substitutions A501V and A501T, as well as an adenine deletion in the mtrR efflux pump promoter and mutated alleles of the PorBIb outer membrane porin protein.3–5 Of concern is a recent study demonstrating that mosaic PBP2 in combination with A501V could lead to ceftriaxone resistance.4

In this study, we used multilocus sequence typing (MLST) to further examine the genotypic diversity of 20 gonococci exhibiting a range of ceftriaxone MICs and including isolates with and without mosaic PBP2 or A501V/T (Table 1). The isolates were from a previous study5 and were retrospectively selected based on the diversity of ceftriaxone MIC, N. gonorrhoeae multiantigen sequence type (NG-MAST)6 and geographical spread; isolates were from Australia (n = 14), Japan (n = 2), Korea (n = 1) and Hong Kong (n = 1), together with two WHO reference strains (WHO-K and WHO-L).7 MLST was performed on all 20 isolates, as previously described.8,9 Briefly, abcZ, adk, aroE, fumC, gdh, pdhC and pgm sequences were amplified by PCR, and then sent for automated fluorescent sequencing at the Australian Genome Research Facility (http://www.agrf.org.au/). MLST types were determined using the Neisseria MLST database (http://pubmlst.org/neisseria/). MLST data were compared with ceftriaxone MICs, NG-MAST type and PBP2 type.

Issue Section:
Research Letters
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