Providing an environment with increased levels of CO2 enhances the growth of many medically important bacteria, including species of Neisseria and Haemophilus. Organisms requiring increased CO2, along with approximately 15% oxygen, are called capnophiles. One of the simplest ways to provide this atmosphere is to incubate them in a closed candle jar. A lit candle in the jar converts some of the O2 in the air to CO2; it soon extinguishes because of insufficient oxygen. Although a candle jar atmosphere contains about 3.5% CO2, enough O2 remains to support the growth of obligate aerobes and prevents growth of obligate anaerobes. Special incubators are also available that maintain CO2 at prescribed levels.
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