O7.4 - Neisseria gonorrhoeae diagnostic escape from a gyrA-based test for ciprofloxacin susceptibility and the impact on zoliflodacin resistance

Background. The etiologic agent of gonorrhea, Neisseria gonorrhoeae, has become resistant to each of the first line antibiotics used to treat it. However, many isolates remain susceptible to ciprofloxacin, leading to the hypothesis that a diagnostic test that accurately reports susceptibility to ciprofloxacin may allow its reintroduction into clinical use. One diagnostic approach is to identify codon 91 in the A subunit of DNA gyrase, gyrA, where coding for the wildtype serine (GyrA^91S) is associated with ciprofloxacin susceptibility and phenylalanine (GyrA^91F) with resistance.
Methods. We used bacterial genetics to introduce gyrA alleles into five strains of N. gonorrhoeae to determine the possibility of diagnostic escape in these genetic backgrounds. We evolved these strains to assess for pathways to ciprofloxacin resistance (minimum inhibitory concentration (MIC) ≥ 1 µg/mL). In parallel, we queried publicly available genomic data and metadata from N. gonorrhoeae clinical isolates (N=11,355) for strains that would be identified as susceptible by gyrA codon 91 assays.


Results. Clinical isolates of N. gonorrhoeae maintained intermediate ciprofloxacin MICs (0.125-0.5 µg/mL) despite reversion of the gyrA allele from phenylalanine to serine, indicating increased risk of treatment failure. We identified 30 N. gonorrhoeae isolates bearing a serine at codon 91 of gyrA as well as a ciprofloxacin resistance mutation at codon 95, four of which had intermediate MICs to ciprofloxacin. Finally, clinical isolates of N. gonorrhoeae bearing GyrA^91S acquired ciprofloxacin resistance through mutations in the B subunit of DNA gyrase (gyrB) that also conferred cross-resistance with zoliflodacin, an antibiotic in phase 3 trials for treatment of gonorrhea.

Conclusion. Diagnostic escape from gyrA codon 91 diagnostics can occur through either reversion of the gyrA allele or expansion of circulating lineages. Diagnostics that guide antibiotic therapy can have unintended consequences, including novel resistance determinants and antibiotic cross-resistance