Effect of types of media on the production of acid from glucose by so-called glucose-negative strains of Neisseria gonorrhoeae.

Typical gonococci metabolize glucose; however, occasional strains of Neisseria gonorrhoeae fail to metabolize glucose when tested on cystine Trypticase agar (CTA) medium, a fact that leads to delay in identification. Certain strains of so-called glucose-negative N. gonorrhoeae do indeed metabolize glucose, depending on the medium used in testing for metabolism of the carbohydrate. Six strains were tested that failed to oxidize glucose with the production of acid when tested on standard CTA medium, yet all produced acid from glucose when supplemented GC medium with a phenol red indicator was utilized. An attempt was made to single out the compound present in CTA that leads to inhibition of metabolism and, occasionally, growth as well. We found that certain ratios of the cystine and Na2SO3 concentrations are inhibitory, including that ratio of the two compounds present in CTA medium; however, L-cysteine, when included in similar concentrations, did not inhibit the metabolic reaction.