1. Nutrition: When bacteria are cultured artificially in vitro, their nutritional needs must be met according to their species orientation. 2.pH: The most suitable pH for most pathogenic bacteria is pH 7.2 ~ 7.6, at which the enzyme activity of bacteria is strong and the growth and reproduction are vigorous. Individual bacteria such as Vibrio cholerae grow best under alkaline conditions of pH 8.4 ~ 9.2. The optimum pH value of mycobacterium tuberculosis is 6.5 ~ 6.8. In the process of bacterial metabolism, sugar decomposes to produce acid, and the pH value decreases, which is not conducive to bacterial growth. 3. Temperature: All kinds of bacteria have different requirements on temperature. The optimum temperature for most pathogenic bacteria to grow is 37℃, so bacteria are usually cultured in an incubator at 37℃ in the laboratory. Individual bacteria such as Yersinia pestis grow best at 28 ~ 30℃. Thermophilic bacteria can grow at 50 ~ 60℃. Marine bacteria are psychrophilic and can grow at 0 ~ 30℃. 4. Gases: Oxygen and carbon dioxide are gases needed for the growth and reproduction of bacteria. According to the oxygen demand of bacteria, bacteria can be divided into three categories: ① obligate aerobic bacteria: bacteria that have a complete respiratory enzyme system, need molecular oxygen as a hydrogen receptor to complete aerobic respiration, and must grow in an aerobic environment, such as Mycobacterium tuberculosis. Some of them are under hypoxic pressure (1). (2) obligate anaerobic bacteria: lacking a perfect respiratory enzyme system, using substances other than oxygen as hydrogen receptors, they can only ferment in an anaerobic environment. When there is free oxygen, they can't use molecular oxygen, but also suffer from H2O2 and superoxide anion (O2-) produced by them in aerobic environment, and even die, such as Clostridium tetanus. (3) facultative anaerobic bacteria: It has two functions of aerobic respiration and anaerobic fermentation, and can grow in aerobic or anaerobic environment, but it grows better when it is aerobic. Most pathogenic bacteria fall into this category. Generally, carbon dioxide produced by bacteria in the process of metabolism can meet the needs. Some bacteria, such as Neisseria meningitidis and Neisseria gonorrhoeae, must be supplied with 5% ~ 10% carbon dioxide to grow in the initial isolation and culture.