microaerophilic

Microaerophilic describes organisms that require oxygen for growth but at lower levels than are present in the Earth's atmosphere. These organisms thrive in environments where the oxygen concentration is reduced, typically about 1–10% O2, and can be harmed by the higher oxygen levels found in air (~21%).

Physiology and ecology: Microaerophiles possess enzymes to detoxify reactive oxygen species but often have lower antioxidant capacity than strict aerobes, making them sensitive to oxidative stress. They may tolerate or require some carbon dioxide in their atmosphere. They are not strictly anaerobic and do not grow best in normal air, but they do not thrive under the high oxygen conditions that support many other aerobes.

Examples and habitats: Classic microaerophiles include Campylobacter jejuni, a leading cause of bacterial gastroenteritis, and Helicobacter pylori, associated with gastritis and ulcers. Microaerophiles are commonly found on mammalian mucosal surfaces, such as the gastrointestinal tract, and in environmental niches like soils, sediments, and aquatic systems where oxygen is limited or diffused.

Culturing and detection: In laboratory settings, microaerophiles are grown under reduced-oxygen, often CO2-enriched atmospheres. This can be achieved with specialized incubators or gas packs that lower oxygen levels to a microaerophilic range. In clinical microbiology, recognizing microaerophilic growth requirements is important for accurate detection and identification of certain pathogens.

Relation to other oxygen requirements: Microaerophiles occupy an intermediate category between aerobes and anaerobes. They are distinct from facultative anaerobes, which can use oxygen or not, and from obligate anaerobes, which are harmed by oxygen.