Causes and pathogenesis of staphylococcal infection

Staph infection is caused by staphylococci, which are gram-positive aerobic organisms. The most pathogenic is Staphylococcus aureus. It usually causes skin infections and sometimes pneumonia, endocarditis, and osteomyelitis. It often leads to abscess formation. Some strains produce toxins that cause gastroenteritis, irritable skin syndrome, and toxic shock syndrome.

The ability to coagulate blood by producing coagulase determines the virulence of some types of staphylococcus.

Coagulase-positive Staphylococcus aureus is one of the most dangerous human pathogens due to its virulence and ability to develop resistance to antibiotics. Coagulase-negative species such as Staphylococcus epidermidis are increasingly associated with hospital-acquired infections, while S. saprophyticus causes urinary tract infections.

Pathogenic staphylococci are usually carried transiently in the anterior nasal passage of approximately 30% of healthy adults and on the skin of 20% of healthy adults. The frequency of transient carriage is higher among hospital patients and hospital medical personnel.

Newborns and nursing mothers are predisposed to staph infections, as are patients with influenza, chronic bronchopulmonary disorders (cystic fibrosis, emphysema), leukemia, tumors, transplants, implanted prostheses or other foreign bodies, burns, chronic skin lesions, surgical scars, diabetes, and intravascular plastic catheters. Patients receiving adrenergic steroids, radiation, immunosuppressants, or antitumor chemotherapy are also at high risk. Predisposed patients may acquire antibiotic-resistant staph from hospital personnel. The hands of health care workers are one of the most common modes of transmission, but airborne transmission is also possible.

Staphylococci are gram-positive, spherical microorganisms, usually located in clusters.

The genus Staphylococcus includes three species: golden (S. aureus), epidermal (S. epidermidis) and saprophytic (S. saprophyticus). Each species of staphylococcus is divided into independent biological and ecological types.

The species of Staphylococcus aureus includes 6 biovars (A, B, C, etc.). Type A is pathogenic for humans and the main causative agent of diseases, the remaining biotypes are pathogenic for animals and birds.

Staphylococci produce toxins and enzymes (coagulase, hyaluronidase, fibrinolysin, lecithinase, etc.), which facilitate the spread of the pathogen in tissues and cause disruption of the vital activity of the cells of the macroorganism.

Pathogenesis of staphylococcal infection

The entry points are the skin, mucous membranes of the oral cavity, respiratory tract and gastrointestinal tract, conjunctiva of the eyelids, umbilical wound, etc. At the site of introduction, staphylococcus causes local inflammation with necrosis and suppuration.

With reduced resistance of the body to pathogenic staphylococcus, under the influence of the damaging effect of its toxins and enzymes, the pathogen and its toxins penetrate from the site of infection into the blood. Bacteremia occurs, intoxication develops. With generalized staphylococcal infection, various organs and tissues (skin, lungs, gastrointestinal tract, skeletal system, etc.) can be affected. As a result of generalization, septicemia, septicopyemia may develop, especially in newborns and children in the first months of life.

In the pathogenesis of food toxicoinfection, the main significance is the massiveness of infection, and both the enterotoxin and the staphylococcus itself are important. In food remains, vomit and excrements of patients, pathogenic staphylococcus is usually found in huge quantities, sometimes in pure culture. However, the pathological process in food toxicoinfection is caused mainly by enterotoxin received with food.