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Causes of staphylococcal infection
Last reviewed: 04.07.2025
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Causes of Staph Infection
Staphylococcal infection is caused by representatives of the genus Staphylococcus of the family Micrococcaceae. Based on the presence of coagulase, staphylococci are divided into coagulase-positive and coagulase-negative. Fourteen of the 27 known species of staphylococci live on human skin. Of these, three species play a role in human pathology: S. aureus (coagulase-positive), S. epidermidis and S. saprophytics (coagulase-negative). S. aureus is most often the etiologic factor in humans. Staphylococci are spherical, immobile, gram-positive microorganisms that occur in groups that resemble a bunch of grapes (Greek staphyle - bunch, coccos - grain).
Of the pathogenicity factors, the most significant are surface proteins - adhesins, which provide 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 via the alternative pathway), protein A (activates complement, natural killers, has superantigen properties); enzymes: catalase, beta-lactamases, lipases, coagulase; toxins (staphylolysins, hemolysins, exfoliants. TSS toxin. leukocidin, enterotoxins A, B, C 1-3, D, E, G, H).
Staphylococci are resistant in the environment, tolerate drying well, but are sensitive to disinfectants, grow on simple nutrient media. They quickly develop resistance to antimicrobial agents.
At a temperature of 70-80 C they die within 30 minutes.
[ Pathogenesis of staphylococcal infection
Staphylococcal infection develops as a result of exogenous infection or autoinfection, when the pathogen is transferred from colonization sites to the injured surface or penetrates the internal environment of the body as a result of invasive procedures (catheterization, endoscopy, etc.). Despite the abundance of pathogenicity factors, staphylococcus is classified as an opportunistic microorganism, since it is part of the normal microflora of the human outer skin. It exhibits pathogenic properties in the presence of additional factors: damage to the outer skin with the formation of a local purulent-inflammatory process, a decrease in local resistance of organs and tissues and general resistance with the development of a generalized infection, and under normal conditions, the 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 is manifested by the accumulation of a large microbial mass and toxin in food products (food poisoning), vaginal tampons (TSS). The local inflammatory reaction in staphylococcal infections always occurs with the participation of polymorphonuclear leukocytes and is purulent. The main causes of death in staphylococcal infection are damage to vital organs: heart (endocarditis), lungs (destructive pneumonia), 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. Of particular danger are health workers - carriers of hospital strains with increased virulence and polyresistance to antimicrobial agents. In medical institutions where patients with increased susceptibility to staphylococcus are concentrated, outbreaks of nosocomial staphylococcal infections are possible (maternity hospitals, neonatology departments, oncohematology, etc.). Staphylococcus aureus are also obligate parasites of cattle, horses, pigs, dogs, monkeys, and occasionally birds. There are known cases of milk infection with staphylococcal mastitis in cows with a subsequent outbreak of food poisoning in humans.
Pathways of transmission of the pathogen are airborne, contact and food. Airborne transmission is possible if the source of the pathogen is a patient with tonsillitis, rhinitis; contact and food transmission - if the source of the pathogen is patients with pustular skin diseases, including medical personnel. The same group serves as a source in the food route of infection, where the transmission factors can be milk and dairy products, confectionery.
Staphylococcal infection is widespread. 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. Infection risk groups are newborns and children under one year old, patients with immunodeficiency states (HIV-infected, intravenous drug addicts, diabetics, etc.).