(P72) Neisseria gonorrhoeae sequence typing for antimicrobial resistance (NG-STAR) for cases of disseminated gonococcal infection (DGI)

Background

In the absence of a cultured isolate for phenotypic antimicrobial susceptibility testing (AST), selection of an appropriate antibiotic therapy for disseminated gonococcal infection (DGI) , or in gonorrhoea infections where ceftriaxone is contraindicated, is challenging. DGI diagnosis often relies on 16s rRNA sequencing of molecular specimens, not cultures. NG-STAR provides guidance on susceptibility to cephalosporins, macrolides, penicillin and fluoroquinolones and also provides typing data for strain comparison.

Methods

The utility of the NG-STAR scheme as a tool where an isolate is lacking was demonstrated utilising 11 DGI isolates collected from a range of infection sites (Table 1) which were referred to the national reference laboratory between 2015 and 2022. Phenotypic susceptibility was determined using gradient MIC strips (Biomerieux) and EUCAST breakpoints. Genomic DNA was extracted using the Qiasymphony DSP DNA mini kit (Qiagen) and Illumina sequencing performed with analysis using PathogenWatch. The phenotypic susceptibility profiles were used to validate the genotypic results.

Results

Eight different NG-STAR profiles were identified in the 11 DGI isolates examined, only NG-STAR types 1387 and 426 were identified in multiple isolates (Table 1). The phenotypic and genotypic results were concordant except for two minor discrepancies for genotypically resistant penicillin with intermediate phenotypic resistance (isolates 2 and 6) and one genotypically resistant cefixime isolate with a minimum inhibitory concentration on the resistance breakpoint (isolate 10, MIC=0.125 mg/L) (Table 1).

Conclusion

In all three genotype/phenotype discrepancies, genotype overestimated resistance compared to phenotypic results, so would not have had a detrimental effect on successful patient treatment. The results support that NG-STAR would be appropriate for use on clinical specimens in future. Within this small collection, incidences where azithromycin would not be an appropriate therapy and where ciprofloxacin would be an appropriate therapy have been identified demonstrating the utility of this scheme in antimicrobial therapy guidance. Further to this, use of NG-STAR would provide a typing database to further our knowledge of DGI causing strains. The variety of NG-STAR types identified in this collection supports previous evidence that DGI is not caused by a single clone.