anaerobes

An anaerobe is an organism that lives and grows in environments lacking oxygen. Some anaerobes are obligate, meaning oxygen is toxic to them; others are aerotolerant or facultative, capable of surviving in the presence of oxygen but not using it for growth.

Most anaerobes obtain energy by fermentation or anaerobic respiration using alternative electron acceptors. This leads to different metabolic end products, such as short-chain fatty acids or gases. Oxygen can be harmful to obligate anaerobes because reactive oxygen species accumulate, and many lack full oxidative defenses.

Anaerobes are widespread in soil, sediments, and the gastrointestinal and oral tracts, where they play roles in digestion and nutrient cycling. Pathogenic anaerobes include species of Clostridium, the Bacteroides fragilis group, and Fusobacterium, which can cause abscesses and tissue necrosis when they invade normally sterile sites.

Clinical infection with anaerobes often requires both antimicrobial therapy and surgical source control. Metronidazole is effective against many anaerobes; other options include beta-lactam/beta-lactamase inhibitor combinations, carbapenems, and clindamycin, chosen according to susceptibility. Proper laboratory handling using anaerobic culture techniques is essential for isolation and identification.

Overall, anaerobes are a diverse and medically important group, contributing to both normal physiology and disease. Their study informs microbiology, ecology, and clinical practice.