Effects of Gaseous CO2 and bicarbonate on the growth of Neisseria gonorrhoeae

Abstract

The quantitative and qualitative growth response of Neisseria gonorrhoeae strains was assessed under the following conditions: incubation in a candle jar (approximately 2.5% ambient CO2) on medium without bicarbonate, incubation in air on medium without bicarbonate, incubation in air on medium with bicarbonate, and incubation in air in a sealed jar on medium with bicarbonate. Incubation in the presence of ambient CO2 (candle jar) resulted in the highest plating efficiencies for the three laboratory strains 9, 62, and 2686. The addition of NaHCO3 to the medium enhanced the growth response in air of all three strains, particularly if incubation was carried out in a closed environment (sealed jar). The qualitative growth response of 34 clinical isolates and laboratory strains was assessed under the same conditions of incubation after the plating of an inoculum containing approximately 2 X 10(6) bacteria. The strains were divided into different classes based on their growth responses. About 40% of the strains grew as well on bicarbonate-containing medium incubated in air in sealed jars as they did on medium without bicarbonate incubated in a candle jar. Ten percent of the strains showed only slight growth on bicarbonate containing medium incubated in sealed jars and appeared to have an almost obligate requirement for ambient CO2. Twenty percent of the strains apparently had partially lost their requirement for gaseous C02 and showed slight growth in air on medium without bicarbonate and slight to moderate growth in air on medium containing NaHCO3. The remaining 30% seemed to have completely lost their requirement for gaseous C02 and/or the bicarbonate anion and grew almost as well in air on medium without bicarbonate as they did in either ambient C02 (candle jar) or on medium containing bicarbonate incubated in a sealed jar. These results suggest that N. gonorrhoeae strains may vary widely in their requirements for CO2 and/or the HCO3-anion. Incubation in the presence of ambient CO2 tends to maximize the growth response on solid medium of those strains, which require it for growth. The presence of ambient CO2 is particularly important if growth is to be obtained after the plating of small inocula. Medium conatining 0.1% NaHCO3, if incubated in a closed environment (sealed jar), apperas to be equivalent to medium without bicarbonate incubated in ambient CO2 in supporting the growth of some but not all strains of N. gonorrhoeae.