capnophilic

Capnophilic is a term used in microbiology to describe organisms that grow best or more robustly in elevated carbon dioxide (CO2) levels compared with ambient air. The prefix capno- derives from Greek kapnos, meaning smoke, and -phile means loving. Capnophiles are contrasted with organisms that do not require increased CO2 and may grow equally well or better in standard atmospheric conditions.

In practice, capnophilic growth is typically achieved by cultivating organisms in environments with higher CO2 concentrations, commonly around 5–10%. This can be accomplished with CO2 incubators, gas-generating bags or jars used in combination with appropriate media. Historically, candle jars were employed to raise CO2 levels and reduce oxygen, though modern laboratories more frequently rely on dedicated incubators or sealed systems to maintain stable CO2.

Common examples of capnophilic bacteria include Neisseria species (such as Neisseria gonorrhoeae and Neisseria meningitidis), Haemophilus influenzae, Streptococcus pneumoniae, and Helicobacter pylori. These organisms may show improved colony formation, growth rate, or viability under elevated CO2, which has practical implications for clinical isolation and diagnostic workflows, particularly for fastidious or respiratory tract-associated pathogens.

While capnophily is a useful concept in selecting culture conditions, the exact CO2 requirement can vary among species and strains. Laboratories tailor incubation conditions to the biology of the target organisms, sometimes using capnophilic conditions in combination with other atmospheric requirements, such as microaerophilic environments.