Chemical composition of bacteria: water, inorganic salts, proteins, sugars, lipids and nucleic acids.
Physical properties of bacteria: optical properties - bacteria are translucent.
Surface area – Bacteria are small in size and have a large relative surface area.
Charged phenomenon - all are negatively charged. Its charging phenomenon is closely related to staining reaction, agglutination reaction, bacteriostatic and bactericidal effect.
Semi-permeability – The cell wall and membrane of bacteria are semi-permeable.
Osmotic pressure - high osmotic pressure in the bacteria.
Depending on the energy source and carbon source used by bacteria, bacteria are divided into two major types of nutrients – autotrophic bacteria and heterotrophic bacteria.
Autotroph: Synthesizes bacterial components based on simple inorganic substances.
Heterotroph: Synthesizes bacterial components and obtains energy from a variety of organic compounds. Heterotrophic bacteria include saprophytes and parasites. All pathogenic bacteria are heterotrophic bacteria, most of which are parasitic bacteria.
Nutrients for bacteria: water, carbon sources, nitrogen sources, inorganic salts, growth factors.
Passive diffusion: Nutrients diffuse from the side of high concentration to the side of low concentration, and their driving force is a concentration gradient that does not require energy.
Active transport system: is the main way bacteria absorb nutrients, which is characterized by the transfer of nutrients from the side of the concentration of low to high concentration, and need to provide energy.
Environmental factors for the growth of bacteria: nutrients, hydrogen ion concentration (pH), temperature, osmotic pressure
Gas - obligate aerobic bacteria: with a complete respiratory enzyme system, can only grow in an aerobic environment.
Microaerobic bacteria: Best grown at low oxygen pressure (5%-6%).
Facultative anaerobic bacteria: both aerobic respiration and anaerobic fermentation, but grow better with aerobics. Most pathogenic bacteria belong to this category.
Obligate anaerobic bacteria: lack of a well-developed respiratory enzyme system (respiratory enzymes with high redox potential, enzymes that break down toxic oxygen groups), and can only be fermented in an anaerobic environment.
Growth and reproduction of individual bacterial individuals
Bacteria multiply in a simple bifiguration manner.
The time required to reproduce a generation is about 20-30 min.
However, a few bacteria have a longer generation, such as Mycobacterium tuberculosis, which is 18 hours.
Growth and reproduction of bacterial populations Lag phase
Logarithmic phase
Stationary phase
Decline phase
