There are many methods of bacterial detection, and the specific type of examination to be taken depends on the choice of different disease conditions, mainly including smear testing, bacterial culture, serological testing, bacterial nucleic acid testing and second-generation sequencing and other detection methods: 1. Smear testing: blood specimens, sputum, urine, stool, cerebrospinal fluid, pleural fluid, ascites and local skin secretions or pus from abscesses can generally be stained by smear. Then the morphology of the bacteria is observed under the microscope, and some bacteria have special morphology, which can be diagnosed early by the method of smear, which is helpful for clinical guidance of antibacterial drugs. 2. Bacterial culture: Bacterial culture is the most reliable test for diagnosing bacterial infection, and bacteria are generally placed in a suitable growth environment in vitro to allow rapid growth and treatment by detecting the source of infection. The disadvantage of bacterial culture is that it cannot help in early diagnosis because it takes a certain amount of time for bacteria to grow, and faster growing bacteria usually take 2-3 days, while some bacteria grow more slowly and may take 1 week or even longer; 3. Serological test: serological test is to isolate the serum in the blood and assist in diagnosis by detecting the antibodies of the corresponding bacteria, such as S. typhi infection, which can be detected by detecting O antibodies and H antibodies of S. typhi to assist in the diagnosis of S. typhi infection. Serological antibodies can be false-positive and false-negative, so compared to bacterial culture, serological antibodies are not very reliable means of detection; 4, bacterial nucleic acid detection: commonly used bacterial nucleic acid detection is mainly polymerase chain reaction, usually called PCR detection, will generally take the bacteria more specific sequence, through the sequence detection diagnosis is whether the bacterial infection, PCR can detect the tiny bacterial nucleic acid, with a high sensitivity; 5, second-generation test 5, second-generation sequencing methods: that is, NGS methods, through the second-generation sequencing of the macrogenome, can detect bacterial infections. However, the human body itself may carry some bacteria in normal tissues, such as skin, respiratory tract, urinary system, vagina, etc. These parts have normal bacterial parasites, and if specimens from these parts are sequenced, bacterial contamination may occur. Therefore, the second-generation sequencing method is usually more reliable for the detection of sterile body fluids, such as pleural fluid, ascites and blood, and after the detection, the patient’s clinical manifestations should be analyzed to determine which type of bacterial infection is present, and whether the detected bacteria are pathogenic.