Characteristics of Bacteria


Some bacteria are fixed, therefore unable to make an autonomous movement, while others are endowed with a more or less marked mobility; the latter have thin vibrating hairs, called flagella. Depending on the number and location of these flagella, the bacteria are divided into:



Habitat and Pathogenicity

The most diverse, some bacteria live in the soil, others in the air or in the water; still others are parasites of plants, animals or humans. As anticipated, however, not all parasites cause damage to the organism that hosts them.

Symbionts are defined as those bacteria that colonize a certain organism giving it a certain advantage (such as the intestinal or vaginal bacterial flora), commensal are those that do not cause harm or advantage, and pathogenic those that damage the organism (produce toxins that are harmful to health of the guest). Note that this division is not clear-cut; many commensal bacteria, for example, can become pathogenic when they grow excessively in number, or when they colonize tissue other than that in which they are normally present (many intestinal bacteria, for example, are responsible for cystitis and vaginitis).

The term infection indicates the ability of a specific bacterium to enter the organism and multiply (the multiplication capacity is called virulence); this is not necessarily synonymous with pathogenicity, which occurs only in the case in which the bacterium produces toxic substances that cause harm to the guest.

Metabolism and Nutrition

the bacteria obtain the energy necessary to meet the needs of their metabolism, essentially by two ways, by capturing solar radiation, or by chemical oxidation; in the first case we speak of photositentic or phototrophic bacteria, while in the second of saprophytic bacteria, chemophytes or parasites. Based on the carbon source used to synthesize organic compounds (proteins, carbohydrates, etc.), bacteria are divided into autotrophs, capable of fixing inorganic carbon dioxide, and heterotrophs, which use the carbon resulting from the demolition of substances organic formed by other organisms.

All bacteria which, like animals, "breathe" oxygen are defined as aerobic; on the other hand, all those bacteria that can live in environments devoid of this gas are anaerobic. Bacteria capable of living both in the absence and in the presence of oxygen are facultative anaerobic, and obligate anaerobic are those bacteria that can survive only in the absence of such gas.


In addition to the basis of the form, the classification of the bacteria can be operated on the GRAM staining (a laboratory procedure in which the bacteria are subjected to some simple treatments). Those that react positively, coloring themselves with dark purple, are classified in the category of GRAM + (GRAM positive), vice versa, those that do not stain (light purple) are called GRAM - (gram negative). This classification has an important value in the medical and pharmacological fields, as GRAM + and GRAM - have different sensitivity to various antibiotics.

Then, obviously, there is a specific taxonomy for bacteria, with division into species, genus, family, classes, Phylum and domains.

Other articles on "Characteristics of Bacteria"

  1. bacteria
  2. bacterial cell
  3. bacteria accessory structures
  4. bacterial toxins
  5. Bacteria: transfer of genetic information
  6. Bacteria: transfer of genetic information
  7. Antibiotics
  8. Categories of antibiotics
  9. Antibiotic resistance
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