What is an Opportunistic Infection?

Normal microorganisms that are parasitic on the human body surface and intestinal tract and microorganisms that are generally not pathogenic in the environment, can cause infection when the resident's immune function is damaged by trauma, which is called opportunistic infection. Opportunistic infections caused by conditioned pathogens are often caused by changes in the bacterial colonies, decreased host immune system function, and dysbiosis.

Opportunistic infection

Opportunity infection concept

Normal microorganisms that are parasitic on the human body surface and intestinal tract and microorganisms that are generally not pathogenic in the environment, can cause infection when the resident's immune function is damaged by trauma, which is called opportunistic infection. Opportunistic infections caused by conditioned pathogens are often caused by changes in the bacterial colonies, decreased host immune system function, and dysbiosis.

Opportunistic infection principle

Opportunistic infections

Opportunistic infections also include microorganisms such as viruses and fungi.

Due to the widespread application of antibiotics, hormones, immunosuppressive agents, tumor chemotherapy and radiation therapy, as well as various catheters and artificial valves that are left in the body, the immune function of the body is impaired to a certain extent, and it is easy to cause conditional pathogenic microorganisms. infection.

(2) Have a deeper understanding of the normal microbiome and microecological disorders. There are a large number of microorganisms on the surface or in the body of normal humans and animals, and they are not pathogenic to their hosts. Some of them are beneficial or necessary for the host, collectively referred to as the normal microbiome. The distribution of normal microorganisms in the host is affected by the structure and physiological state of the host. It is estimated that the total weight of the microorganisms carried by the human body is about 1271 g, of which the gut occupies 1000 g, the oral cavity 20 g, the nose 10 g, the eye 1 g, the lung 20 g, and the vagina 20 g. That is, the human gastrointestinal microbes account for about 78% of the total human microbes, mainly including Lactobacillus, Escherichia coli, Bifidobacterium, Streptococcus, etc. Among them, anaerobic bacteria have an absolute advantage, accounting for more than 95% of the total number of intestinal bacteria, which is 1,000 to 10,000 times more than aerobic or facultative anaerobic bacteria. In the course of long-term historical evolution, as a result of continuous adaptation of microorganisms, there is a dynamic equilibrium between microorganisms and their hosts, between microorganisms and microorganisms, and between microorganisms, hosts, and the environment, forming an interdependent and mutually restrictive system. As a result, a micro-ecological balance is formed between the normal microbiome, the host, and the environment.

Under the influence of the external environment (such as trauma, improper use of antibiotics, etc.), the microecological balance between the normal microbiota or between the normal microbiota and its host is changed, causing diseases or pathological phenomena to appear, called microecological disorders.

Causes of Opportunistic Infections

There are many factors that cause microecological disorders. From the perspective of clinical microbiology, it mainly involves the application of surgery, antibiotics, and radiation, which affects the host's internal physiological environment or the resistance of microorganisms. E.g:

(1) Surgery: The operations of various organs of gastrointestinal surgery, such as colectomy, gastrectomy, and intubation, have disrupted the host's normal physiological anatomy and intestinal microecological environment, resulting in microecological disorders or bacterial flora imbalances. Electrolyte malabsorption, steatorrhea, etc.

(2) Antibiotics: Due to the widespread use of antibiotics, a large number of resistant strains have rapidly increased through the mutation and selection of bacteria under the action of antibiotics. The drug-resistant strains are encoded by the R plasmid. The R plasmid is composed of two parts: resistance transmission factor (RTF) and resistance determinant (r determinant). The function of RTF is similar to that of the F plasmid, which can encode the generation of pili and transfer by conjugation; the r determinant encodes resistance to antibacterial drugs, and its gene sequence can carry multiple transposons (Tn), causing Multiple drug resistance, up to 10 drug resistances on one plasmid. Drug-resistant plasmids transferred by sexual pili conjugation are called zygosity plasmids. Non-zygote particles cannot be transferred by sexual pili conjugation, but can be transferred by phage transduction. As most normal flora become antibiotic-resistant strains, nosocomial infections can easily occur. Many patients from remote areas had a third strain isolated from the intestinal tract and other parts when they were first admitted to the hospital, but soon turned into a drug-resistant strain. This is because medical staff in hospitals and patients who have been in hospital for a long time have drug-resistant strains, which can be transmitted to new patients through contact, air, and household appliances.

(3) Radiation: After a certain amount of radiation is received by a person or animal, the normal microbiome and microecological balance are destroyed. After the defense mechanism in the host is destroyed, the function and number of phagocytes are reduced, and the immune response capacity is reduced. Intestinal microorganisms (such as E. coli, Pseudomonas aeruginosa, etc.) can enter tissues and bloodstream to cause lesions. On the other hand, because the bacteria's resistance to radiation is much higher than that of the host cell, after the role of radiation in the host, the drug resistance and toxicity are often enhanced, which promotes microecological disorders.

(4) Opportunistic infections due to decreased immune function are also seen in chemotherapy for tumor patients, organ transplantation (using cyclosporine) and AIDS patients. They are susceptible to fungi, mycobacteria, pneumocystis carinii, etc. .

Be vigilant against conditionally pathogenic microorganisms and use corresponding methods for detection and identification. Use sensitive antibiotics in treatment. In addition, pay attention to the recovery of patients' immune function.