Bacteria can be classified into aerobic and anaerobic, with the former requiring oxygen to survive and the latter not relying on oxygen. Anaerobic bacteria can become virulent pathogens and are more resistant to standard antibiotic therapies. Identifying the type of bacteria is important in treating infections.
Bacteria can be classified into aerobic and anaerobic. The main difference between the two is the fact that aerobic bacteria require oxygen to stay alive whereas anaerobic bacteria do not rely on oxygen for metabolic processes and survival. While aerobes are able to thrive in habitats that have abundant oxygen, anaerobes can die in the presence of oxygen. This type of bacteria has a growth advantage in areas of the body not exposed to oxygen and can become virulent pathogens. The difference in the ability to utilize oxygen between aerobes and anaerobes is important in the treatment of bodily infections.
The classification of bacteria can be based not only on whether or not they need oxygen, but also on how they use it. Obligate aerobes are microorganisms that need oxygen to survive and die in its absence. An example is the Bacillus anthracis bacterium. Obligate anaerobes are organisms that die when exposed to oxygen, such as Clostridium tetani and Clostridium botulinum, which cause tetanus and botulism, respectively.
Facultative anaerobes can live in the presence or absence of oxygen, but prefer to utilize oxygen. Examples of this type include Escherichia coli (E. coli) and Staphylococcus, or simply staphylococcus. E. coli subtypes, such as O157:H7, cause bloody diarrhea, while staph is known to cause skin infections such as boils, folliculitis, and impetigo. When a deep skin tear becomes infected with staph, a more serious form of infection called cellulitis can occur.
The other two classifications are microaerophilic bacteria and aerotolerant bacteria. Microaerophiles can live in habitats that have lower oxygen levels than the atmosphere. Examples of microaerophiles are Helicobacter pylori, which causes peptic ulcer disease, and Borrelia burgdorferi, which causes Lyme disease.
Aerotolerant anaerobic bacteria have no use for oxygen but are not adversely affected by its presence. An example is the genus Lactobacillus, which is normally found in the intestines, skin and vagina. When the Lactobacillus populations in the vagina become depleted, bacteria such as Gardnerella vaginalis and Bacteroides multiply, leading to bacterial vaginosis.
The bacteria are grown in a microbiology laboratory to provide an important clue as to their identity. In particular, when cultured in test tubes, the following observations can be documented. Obligate aerobes congregate at the surface of the culture medium to maximize oxygen uptake, while obligate anaerobes congregate at the bottom to keep away from oxygen. Facultative bacteria collect near the top, while microaerophiles collect near the top, but not at the surface. Aerotolerant anaerobes are distributed uniformly along the depth of the soil.
Identifying whether a bacterium is aerobic or anaerobic is important in treating bacterial infections. Treating infections caused by anaerobic bacteria is often more challenging because they are resistant to standard antibiotic therapies. For example, treatment of bacteria such as Bacillus fragilis usually includes a combination of antibiotics such as piperacillin/tazobactam, imipenem/cilastatin, amoxicillin/clavulanate and metronidazole plus ciprofloxacin or gentamicin.
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