anaërobes

Anaërobes, commonly referred to as anaerobes, are organisms that do not require oxygen for growth and may be inhibited or killed by atmospheric oxygen. They inhabit diverse ecological niches and play important roles in health, disease, and environmental processes. Anaërobes are classified into several groups: obligate (or strict) anaerobes, which cannot tolerate oxygen; facultative anaerobes, which can grow with or without oxygen; aerotolerant anaerobes, which do not use oxygen but tolerate its presence; and microaerophiles, which require low but not zero levels of oxygen. Metabolically, anaërobes rely on fermentation or anaerobic respiration using alternative electron acceptors such as nitrate, sulfate, or carbon dioxide. Their energy yield is generally lower than that of oxygen-using counterparts.

Habitat and significance: obligate anaërobes are common in the gastrointestinal tract, oral cavity, deep sediments, and soil layers where oxygen is scarce. Many anaërobes are beneficial components of the gut microbiota, aiding digestion, vitamin synthesis, and colonization resistance against pathogens. Others can cause disease when they overgrow or invade normally sterile tissues; notable examples include toxins produced by Clostridium species causing botulism or tetanus, and infections by Bacteroides and other anaerobes after tissue injury. In industry and the environment, anaërobes participate in fermentation, biogas production, and bioremediation.

Detection and culture: anaërobes require oxygen-free conditions for growth and are cultured in specialized anaerobic jars or chambers with oxygen-scavenging systems. Growth is often slower and more fastidious than that of aerobes, and clinical sampling requires careful handling to preserve viability.