Improved Neisseria gonorrhoeae culture media without atmospheric CO₂

Bacterial culture on solid media is the crucial step in diagnosing Neisseria gonorrhoeae infections and is the gold standard for determining their antimicrobial resistance profile. However, culture of Neisseria spp. can be challenging in resource poor areas, relying on specialist incubators or other methods of supplying 5% CO₂ for growth of the bacteria. Even when such incubators are available, the CO₂ to run them may be scarce; there were CO₂ shortages during the COVID-19 pandemic, for example. Although culture jars with gas packs or candles can be used, these are inefficient in terms of use of incubator space and researcher time. To achieve simplicity in culturing of N. gonorrhoeae, the standard Oxoid GC agar base medium, made with the Kellogg's glucose and iron supplements was improved with the addition of 0.75 g/l sodium bicarbonate (NaHCO₃), which is inexpensive and readily available. This improved media in a standard incubator performed as well as standard Oxoid GC agar media with supplements in a 5% CO₂ incubator. Chocolate agar and Thayer-Martin agar with sodium bicarbonate were also developed, with all showing good growth of N. gonorrhoeae without the need for atmospheric CO₂. KEY POINTS: • Neisseria spp. (N. gonorrhoeae, N. meningitidis) require atmospheric CO₂ to grow. • Sources of CO₂ may be scarce depending on geography and lab supply availability. • We have developed GC, Chocolate, and Thayer-Martin media that does not need CO₂.