Opportunistic pathogens, also known as opportunistic pathogens, refer to pathogens that do not cause disease in humans under normal conditions but can cause disease under certain special conditions. The criteria for opportunistic infection include: 1. Disruption of the intestinal flora, where there is a balanced relationship between normal beneficial bacteria and the host, as well as between normal beneficial bacteria. If this balance is disrupted, opportunistic pathogens can reproduce abnormally and increase their pathogenicity. 2. When the body’s immune function decreases, normal beneficial bacteria can cause disease after entering the body’s tissues or bloodstream. 3. Some bacteria leave their normal resident sites and grow and reproduce in other locations, causing disease. The criteria for opportunistic pathogens generally only include the above three.

After patients with AIDS enter the AIDS stage, due to the decreased immune function, opportunistic infections are easily produced, among which the most common and widely known is pneumocystis pneumonia. Pneumocystis is a type of bacteria that can cause chronic cough, fever, respiratory discomfort, and decreased oxygen partial pressure in AIDS patients. Severe patients may progress to respiratory failure, and patients may die due to persistent respiratory discomfort leading to the failure of multiple organs in the body. In addition to pneumocystis pneumonia, patients may also develop cryptococcal meningitis, candidal esophagitis, herpes zoster, giant cell retinitis, and other diseases. In addition to infections, patients may also develop secondary malignant tumors, such as lymphoma and Kaposi’s sarcoma.

In fact, humans live in a natural environment filled with pathogens, viruses, and other microorganisms, including the oral cavity and gastrointestinal tract, which are all rich in pathogens and viral infections. These microorganisms may all become pathogenic bacteria. When the body’s immune system is stronger than the pathogenicity of the pathogens, the body can coexist with them, making these microorganisms become resident bacteria, and even the bacteria in the gastrointestinal tract can assist the body in digesting and absorbing food, becoming probiotics.

However, when the body’s immune ability decreases, the balance between the body and pathogens will be destroyed, causing the original resident bacteria, probiotics, to become pathogenic bacteria. For example, the gastrointestinal resident bacteria may become pathogens of secondary infection after long-term use of antibiotics, and the protozoa commonly found in the oral cavity may also become pathogens of oral candidiasis when the immune system is low.