Introduction Current surveillance of antibiotic resistance in Neisseria gonorrhoeae (NG) relies heavily on the culture of NG. However, culture of NG is challenging due to demanding nutritional and growth requirements of this micro-organism. As a result, surveillance data are limited to only cultured strains while of >50% of Dutch NG positive patients no NG is cultured (data from Dutch Gonococcal Surveillance Program). In this study we compared results from direct detection of mosaic penA with detection of cultured strains to investigate feasibility of direct molecular resistance surveillance.
Methods A convenience sample of 106 NG positive samples of which positive NG culture results were available (46 urine, 9 genital swabs, 35 anorectal swabs and 16 oropharyngeal swabs) were collected between 2013–2015. Presence of mosaic penA was determined by real-time PCR. All positive findings were confirmed with sequencing. MICs on cultured NG were determined using E-tests.
Results LOD determinations of the in-house mosaic penA PCR in comparison to routine NAAT (using COBAS 4800, Roche Diagnostics) showed that the mosaic penA assay was slightly less sensitive than the commercial NAAT. In samples with very low NG loads, mosaic penA detection might be false-negative. Of 106 NG positive samples, 11 samples showed the presence of mosaic penA (6 urine, 4 oropharyngeal and 1 anorectal swab).Of these 11 samples, NG isolates were re-cultured from 8 samples and all isolates contained the mosaic penA gene. MIC values for ceftriaxone varied between 0.016 and 0.094 mg/L and thus no reduced susceptibility was observed. Although cross-detection with mosaic penA from N. meningitidis is possible, no evidence of this was shown in this study.
Conclusion In conclusion, this study indicates that detection of mosaic penA directly from clinical samples is feasible and that results match detection of penA from clinical isolates obtained from these samples. Direct detection of antibiotic resistance genes would show an insight in resistance surveillance of strains that are not or cannot be cultured.