A comparison of a single agar plate versus a bi-plate for culturing Neisseria gonorrhoeae

Culture remains essential for antimicrobial resistance profiling for gonorrhoea. However, the sensitivity of culture for gonorrhoea is low. This study aimed to compare positivity rates of culture for Neisseria gonorrhoeae using a gonococcus (GC) bi-plate containing selective and non-selective agar versus a single GC plate containing selective agar only, and assess the impact of clinician inoculation training and timing between a nucleic acid amplification test (NAAT) and culture on culture positivity.

A cross-sectional study was conducted at Melbourne Sexual Health Centre between April and June 2021. Clients undergoing gonorrhoea testing provided samples for both NAAT and culture, with alternating use of GC bi-plates and single GC plates over 2-week intervals. Clinicians received training on inoculation techniques before the study. A retrospective analysis of culture positivity before training was also performed. Culture positivity was compared between plate types, pre- and post-training, and across different time gaps between NAAT and culture.

Among 276 clients included, there was no difference in culture positivity between GC bi-plate and single plate across all anatomical sites (P = 0.439). Oropharyngeal culture had the lowest positivity rates (44.3% bi-plate vs 36.2% single plate, P = 0.382). There was no significant difference in culture positivity before and after training staff on inoculation technique (P = 0.782), nor if the cultures were performed 1-5 days between positive NAAT and culture compared with 6-14 days.

This study found no significant difference between GC bi-plate and GC single plate in detecting N. gonorrhoeae. Inoculation training and delayed culture post-NAAT did not significantly impact culture positivity. Improving culture methods remains critical for antimicrobial resistance surveillance.