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The Classification of Gram Aerobes & Anaerobes

In bacteria, some varieties are classified as aerobes, requiring oxygen to respire, and others are anaerobes, which means they can function in the absence of oxygen or even die in the presence of oxygen. Bacteria can also be classified using the gram-staining technique, which is a laboratory technique designed to detect peptidoglycan, whose presence or absence determines whether a bacteria possess a cell wall.

Gram Positive
- Gram positive bacteria retain crystal violet dye and stain dark blue or purple during the gram staining process. One of the primary features which classifies a bacteria species as gram positive is the absence of an outer membrane . They possess a thick, multi-layered peptidoglycan layer, which is a mesh-like layer of sugars and amino acids, forming part of the cell wall. They also lack a periplasmic space, which is a space between the inner and outer membranes. In addition, gram positive bacteria are classified by their high resistance to physical disruption, sodium azide and drying.
Gram Negative
- Bacteria are classified as gram negative if they possess an outer membrane and a thin, single-layered peptidoglycan layer. During the gram staining process they react by decolorizing to accept a safranin counterstain, and they stain red. They possess a low resistance to physical disruption, a low resistance to sodium azide and a low resistance to drying.
Classifying Aerobes
- Aerobic bacteria require oxygen in order to thrive. Aerobic bacteria come in both gram positive and gram negative varieties. Some varieties of gram positive rod-shaped bacteria of the genus bacillus are classified as aerobes -- these include Bacillus cereus, Bacillus stearothermophilus and Bacillus subtilis. The gram positive genus Corynebacterium includes Corynebacterium diphtheriae which causes the disease diphtheria. Other gram-positive aerobic genus include Kurthia, Micrococcus and Mycobacterium. Gram-negative aerobes include members of the genus Aquaspirillum belonging to the family Spiralaceae, which are found in freshwater.
Classifying Anaerobes
- Anaerobic bacteria are those bacteria which are able to thrive in the absence of oxygen. Faculative anaerobes can grow in the presence of oxygen but do not require it, while obligate anaerobes die in the presence of oxygen and thus rely on other gases such as methane. Examples of gram positive, obligate anaerobes include Clostridium histolyticum, C. acetobutylicum and C. sporogenes. Major genera of gram negative anaerobic bacilli include Bacteroides, Fusobacterium, Prevotella and Poryphyromonas.

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