Carbon dioxide requirement of Neisseria gonorrhoeae growing on a solid medium

A survey of 120 isolations of Neisseria gonorrhoeae from male patients showed that 47 (39%) isolates were unable to produce visible colonies without a supply of exogenous carbon dioxide. Of 63 strains, 25 strains required CO2 for isolation but none exhibited a CO2 requirement beyond subculture 4. CO2-requiring strains deprived of CO2 appeared to lose their colony-forming ability exponentially in an environment otherwise conductive to growth. The CO2 requirement was found to be linked to the initiation of growth. An agar-to-agar replica-plating device was used to study the early stages of colonial growth. The CO2 requirement was also found to correlate with the various phases of the colony growth cycle, such that it was required during lag phase, not required during the phase of rapid growth, and returned as colonies aged. These results are discussed.