What are bacteria?

The bacteria - single-celled plant organisms, many of which are the causative agents of infectious diseases in humans.
The dimensions of bacteria range from tenths of a micron to several microns. The shape of the bacteria are divided into:

1) cocci - bacteria are spherical;

2) rod-shaped bacteria;

3) spirillum - Bacteria shaped crimped filaments;

4) vibrios - bacteria in the form of bent rods. Spore-forming bacillus called bacilli, do not form spores - bacteria.

Among the bacilli are distinguished sticks diplobatsilly, streptobatsilly.

All coated bacteria cell membrane, which tightly fits the cytoplasmic membrane. The shell on the outside is surrounded by many types of bacteria layer of mucus - a capsule, which defines a number of properties of bacteria, in particular, their virulence (eg, pneumococci). Many bacteria have flagella and are able to actively move in the liquid medium. The number and nature of bacterial flagella location on the cell surface - one of the most important characteristics of the bacteria. Adjacent to the envelope cytoplasmic membrane regulates the process of penetration of substances into cells and metabolic products outlet to the external environment.

The main part of the bacterial cell membrane-delimited cytoplasm - when viewed under a microscope looks like a homogeneous mass, it lacks typical of most other plant cell organelles - the plastid. Due to the complex molecular structure of the cytoplasm it biochemical reactions occur that make metabolism - metabolism of the bacteria in which nutrients are synthesized from a number of components, including defining their pathogenicity.

The cytoplasm contains a bacterial enzymes - biological catalysts of protein nature, which is impossible without the participation of metabolic reactions. Unlike the cells of higher organisms, the nuclear structure of the bacteria - nucleoid - is not separated from the cytoplasmic membrane, has no definite shape and divided, by amitotic. Division nucleoid precedes the bacterial cell division. Sexual reproduction process in bacteria is the transfer of genetic material from the male cells into female by direct contact of two bacteria - conjugation (see Genetics of microorganisms.).

Put on a solid nutrient medium bacteria begin to grow - increasing weight of individual cells and their number - formed bacterial colonies. The process of bacterial growth in the liquid medium can be divided into four phases, corresponding to the different stages of growth and reproduction of the bacterial culture. In virtually divided into the first hour or two hours after the introduction of bacteria into the nutrient medium, but increase in size. This period is called the lag phase.

Then comes the logarithmic growth phase, during which the bacteria are divided at a constant speed (it takes several hours). It replaces the stationary phase, when the number of cells in the culture remain constant. Finally, the cells begin to die in culture - the phase of logarithmic bacteria destruction.

Nutritional needs diverse bacteria: some forms are able to grow using simple connections - carbon dioxide and ammonium ions; It requires the presence of other organic nitrogen sources, carbon, and other complex organic materials, including vitamins.

The bacteria also need a sufficient humidity environment, the optimum amount of oxygen and m. P.. With a variety of adverse effects comes the death of the bacteria. The strongest bactericidal effect have a raised temperature, ultraviolet rays and some chemical compounds. These factors are used, as a rule, the sterilization.
Some types of bacteria form spores that can persist for a long time in adverse conditions (high temperature drying).

The most important characteristic of bacteria is their antigenic composition. Bacterial antigens are divided into several groups (for example, flagellar antigens, capsular antigens and m. P.). There are group antigens - are common to several types of bacteria, and specific - unique to this type of bacteria. The antigenic properties of the bacteria are the basis for the formation of specific immunity (see.). Diagnosis of many bacterial diseases is based on determining differences in their bacterial antigenic structure.

The basis of pathogenicity Bacteria is their ability in reproduction in the human body form toxins. Some pathogenic bacteria can not reproduce in macroorganism but emit powerful exotoxins that are getting into the human body (eg, food) to cause disease. In some cases (for example, with the weakening of host defense reactions) can cause disease and bacteria are not usually considered to be pathogenic to humans.

Bacterial growth factors (bacterial vitamins, bios) - organic substances necessary for life bacteria cells themselves are not able to synthesize. Each species or strain of bacteria requires a certain set and the concentration of these substances are added to the nutrient medium. By BIOS include amino acids and purine bases piramidinovye, vitamins (thiamine, riboflavin, pantothenic acid, folic acid, nicotinamide, inositol, pyridoxine, para-aminobenzoic acid, menadione, etc.), Choline, hemin, enzymes. The absence of these substances in the medium leads to bacteriostasis.

L-form bacteria - special filter shapes are well known bacteria, resulting in the destruction of the cell membrane or the loss of the ability of its education. Described L-shaped hemolytic streptococci, pneumococci, micrococci, Neisseria gonorrhoeae, Pasteurella, Escherichia coli, causative agents of dysentery, etc. Most often, the L-shaped bacteria -. Are spherical corpuscles, smaller than bacteria, or approaching it.
L-shaped form when exposed to bacteria penicillin, lysozyme, respiratory poisons;

They also arise when a lack of the substances necessary for bacterial cell wall synthesis. Upon termination of the agent L-shape is gradually transformed into the original microorganisms.