Bacteria - celled plants, many of which are pathogens of infectious diseases.
The sizes of bacteria ranges from a tenth of a micron to several microns. Form bacteria are divided into: 1) cocci bacteria spherical form; 2) rod-shaped bacteria; 3) spirilli - bacteria, having the form of twisted yarns; 4) the Vibrio cholerae bacteria in the form of curved sticks. Spore-forming Bacillus called bacilli that do not form spores - bacteria. Among bacilli distinguish sticks, diplomaticly, streptobacillus.
All bacteria are covered with cellular membrane, which is tightly fits the cytoplasmic membrane. Shell outside surrounded by many types of bacteria with a layer of mucus - capsule defines a number of properties of bacteria, in particular their virulence (for example, pneumococci). Many bacteria have flagella and is able to move in a liquid medium. The number and nature of location flagella on the surface of the bacterial cell is one of the most important characteristics of bacteria. Adjacent to the shell cytoplasmic membrane regulates the process of penetration of various substances into the cell and out of metabolic products into the environment. The main part of the bacterial cell is separated by a membrane cytoplasm - when viewed under a microscope appears as a homogeneous mass, it does not typical of most other plant cell organelles - plastids. Thanks to complex molecular structure of the cytoplasm in it are biochemical reactions that make up the metabolism of the metabolism, during which they synthesize of nutrients a number of components, including defining their pathogenicity. The cytoplasm contains bacterial enzymes - biological catalysts protein nature, without which impossible the reactions of metabolism. Unlike the cells of higher organisms, nuclear structure bacteria - nucleoid is not separated from the cytoplasm by a membrane that is formless and shares mitoticeski way. Division of nucleoid precedes the bacterial cell division. Sexual process of reproduction of bacteria is the transfer of genetic material from a male cells into female with the direct contact of two bacterial conjugation (see Genetics of microorganisms).
Placed on firm nutrient bacteria begin to grow - increasing mass of individual cells and their number is formed bacterial colonies. The process of growth of bacteria in a liquid nutrient medium can be divided into four phases, corresponding to different stages of reproduction and growth of bacterial cultures. In the first hour or two hours after entering into the nutrient medium bacteria practically are not split, but the increase in size. This period is called Lactasoy. Then comes the logarithmic growth phase, during which the bacteria share with constant speed (lasts a few hours). It is replaced by the stationary phase, when the number of cells in culture remains constant. Finally, cells in culture begin to die - phase begins logarithmic the death of the bacteria.
The nutritional requirements of bacteria varied: some forms can grow using simple compounds - carbon dioxide and ammonium ions; others require the presence of organic sources of nitrogen, carbon and other complex organic substances, including vitamins (see below Bacterial growth factors). Bacteria also require sufficient humidity of environment, optimal amount of oxygen and so on (see Nutrient medium). At various adverse impacts comes the death of the bacteria. The strongest bactericidal action (see the Bactericidal action) have increased temperature, ultraviolet rays and some chemical compounds. These factors are used, as a rule, during sterilization.
Some species of bacteria form sporescapable of long persisted in adverse conditions (high temperature, drying).
The most important characteristic of bacteria is their antigenic composition. Antigens bacteria are divided into several groups (for example, the flagellar antigen, capsular antigens and so on). There are group antigens - General for several types of bacteria, and specific characteristic only of this type of bacteria. Antigenic properties of bacteria are the basis for the formation of specific immunity (see). Diagnosis of many bacterial diseases based on the definition of the differences of the bacteria in their antigenic structure (see Serological studies).
In the basis of pathogenicity (see) bacteria is their capacity for reproduction in the body to form toxins (see). Some pathogenic bacteria are not able to multiply in the host, there are strong exotoxins that, once in the human body (for example, with food)that cause disease. In some cases (for example, with the weakening of protective reactions of the organism), the disease may be caused by bacteria, not generally considered to be pathogenic for humans.
Cm. also Bacteriological examination.
Bacterial growth factors (bacterial vitamins, BIOS) - substances of organic origin, necessary for vital functions of bacteria that are the cells themselves cannot synthesize. Each strain or type of bacteria needs a certain set and the concentrations of these substances, which add to the nutrient medium. To the BIOS are amino acids, purine and pirimidinov Foundation, vitamins (thiamin, Riboflavin, Pantothenic acid, folic acid, nicotinamide, Inositol, pyridoxine, para-aminobenzoic acid, menadione and others), choline, gemin, enzymes. The absence of these substances in the environment leads to the bakteriostaz.
L-form bacteria - specific filtering form well-known bacteria, resulting from the destruction of cell membrane or loss of the ability to her education. Described in L-shape hemolytic streptococci, pneumococci, mikrokokkov, gonokokkov, pasteurellosis, coliforms, pathogens of dysentery and other most commonly L-form bacteria is spherical bullock, smaller than bacteria, or approaching them.
L-forms are formed under the action of bacteria penicillin, lysozyme, respiratory poison; they are also the lack of nutrients necessary for the synthesis of membrane of bacterial cells. Upon termination of the agent, the L-shape gradually turn into a source microorganisms.