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Causes of Staphylococcal Infection
Last reviewed: 23.04.2024
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Causes of Staphylococcal Infection
Staphylococcal infection is caused by representatives of the genus Staphylococcus family Micrococcaceae. By the presence of coagulase, staphylococci are divided into coagulase-positive and coagulase negative. On the human skin, 14 of the 27 known types of staphylococcus live. Three of them play a role in human pathology: S. Aureus (coagulase-positive), S. Epidermidis and S. Saprophytics (coagulase-negative). The aetiological factor in a person most often becomes S. Aureus. Staphylococci are globular, fixed Gram-positive microorganisms, arranged in groups that resemble a bunch of grapes (Greek staphyle - bunch, coccos - grain).
Of pathogenicity factors, the most important are surface proteins - adhesins, which ensure adhesion (adhesion) of staphylococcus to the cell membrane; capsule, protecting staphylococcus from complement-mediated phagocytosis; components of the microbial cell that initiate the inflammatory reaction, in particular teichoic acids (activate the complement system, hemostasis system, kallikrein-kinin system), protein A (activates complement, natural killers, possesses properties of superantigen); enzymes: catalase, beta-lactamase, lipase, coagulase; toxins (staphylolysins, hemolysins, exfoliants, toxin, STS leukocidin, enterotoxins A, B, C 1-3, D, E, G, H).
Staphylococci are stable in the environment, they tolerate drying well, however they are sensitive to disinfectants, they grow on simple nutrient media. Rapidly develop resistance to antimicrobial agents.
At a temperature of 70-80 C, they die within 30 minutes.
[The pathogenesis of staphylococcal infection
Staphylococcal infection develops as a result of exogenous infection or autoinfection, when the pathogen from colonization sites is transferred to the injured surface or penetrates into the internal environment of the body as a result of invasive procedures (catheterization, endoscopy, etc.). Despite the abundance of factors of pathogenicity, staphylococcus is classified as conditionally pathogenic microorganisms, since it is a part of the normal microflora of human outer covers. He exhibits pathogenic properties in the presence of additional factors: damage to the outer covers with the formation of local purulent-inflammatory process, reduction of local resistance of organs and tissues and general resistance with the development of generalized infection, and under normal conditions penetration of staphylococcus into the blood does not lead to the development of sepsis. Staphylococcal bacteremia is observed in many severe infectious diseases. The toxic effect of staphylococcus manifests itself when a large amount of microbial mass and toxin is accumulated in food products (food poisoning), vaginal tampons (STS). Inflammatory local reaction in staphylococcal infections always occurs with the participation of polymorphonuclear leukocytes and is purulent. The main causes of death with staphylococcal infection are the defeat of vital organs: the heart (endocarditis), the lungs (destructive pneumonia), the brain (meningitis, abscess), septic shock. Thrombohemorrhagic syndrome, in particular thromboembolism of the main vessels.
Epidemiology of staphylococcal infection
The source of the pathogen is healthy carriers and patients with any form of staphylococcal infection. Particular danger is posed by medical workers - carriers of hospital strains that have increased virulence and multidrug resistance to antimicrobial agents. In medical institutions, where patients with increased susceptibility to staphylococcus are concentrated. Outbreaks of nosocomial staphylococcal infections (maternity homes, neonatology, oncohematology, etc.) are possible. Staphylococcus aureus is also an obligate parasite of cattle, horses. Pigs, dogs, monkeys, and occasionally birds. There are cases of milk inflation during staphylococcal mastitis in cows with a subsequent outbreak of food poisoning in humans.
Ways of transmission of the pathogen are airborne, contact and food. An air-drop path is possible if the source of the pathogen is a sore throat, rhinitis; contact and food - if the source of the causative agent of infection are patients with pustular skin diseases, including medical personnel. The same group serves as a source for the food pathway of infection. Where the transmission factors can be milk and dairy products, confectionery.
Staphylococcal infection is ubiquitous. Diseases occur throughout the year. Both sporadic cases and epidemic outbreaks are recorded.
Susceptibility to staphylococcal infections is low, but the constant risk of infection contributes to the fact that most adults (up to 40%) develop antibodies against staphylococcus and its toxins. Groups of risk of infection - newborns and children under one year, patients with immunodeficiency states (HIV-infected, intravenous drug users, patients with diabetes mellitus, etc.).