Comparison of deferred and bedside culture of Neisseria gonorrhoeae: a study to improve the isolation of gonococci for antimicrobial susceptibility testing

Antimicrobial resistance of Neisseria gonorrhoeae is globally spread and threatening. Culturing of N. gonorrhoeae is the only method to collect live isolates for investigation antimicrobial resistance profile. Therefore, quality assessment of N. gonorrhoeae culture is essential for successful isolation of gonococci. This study was conducted to evaluate deferred and bedside culture of N. gonorrhoeae depending on the year season and temperature condition of transport media temporary storage.

Urogenital swabs from 46 symptomatic heterosexual patients with gonorrhoea and subculture of N. gonorrhoeae in 46 suspensions in concentrations 1.5 × 108 CFU/ml were subjected to the study. Non-nutritive transporting medium Amies Agar Gel Medium with charcoal (Copan Diagnostics Inc., Brescia, Italy) was used for deferred culture and selective Chocolate agar TM+PolyViteX VCAT3 (BioMérieux, Marcy-l'Étoile, France) for both tested methods of culture.

The specificity of both bedside and deferred methods of culture was 100%. The sensitivity of deferred culture was higher than of bedside culture (82.6% vs 47.8%, p<0.0005). Deferred culture showed significantly higher sensitivity comparing to bedside culture in summer (100% vs 50%, p=0.003), and comparably the same as for bedside culture in autumn, winter and spring.

The viability of N. gonorrhoeae subcultures was significantly higher in refrigerated samples from transport media than from ambient one after exposition from 48 to 96 hours. Optimal viability of N. gonorrhoeae was observed when transport swabs were kept refrigerated up to 48 h (73.9-93.5%) or ambiently – up to 24 h (87%). Updating laboratory guidelines regarding sampling and timely specimen processing might improve gonococcal culture performance.