Causes and pathogenesis of staphylococcal infection

Staphylococcal 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 the formation of an abscess. Some strains produce toxins that cause gastroenteritis, irritated skin syndrome and infectious-toxic shock.

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

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

Pathogenic staphylococci are usually transported transiently in the anterior nasal passage in approximately 30% of  healthy  adults and on the skin of 20% of healthy adults. Among hospital patients and medical staff of hospitals, the frequency of transient carriage is higher.

Newborns and nursing mothers are predisposed to staphylococcal infections, as well as patients with influenza, chronic bronchopulmonary disorders (cystic fibrosis, emphysema), leukemia, tumors, grafts, implanted dentures or other foreign bodies, burns, chronic skin lesions, surgical scars, diabetes and intravascular plastic catheters. The high-risk group also includes patients receiving adrenosteroids, irradiation, immunosuppressants or antitumor chemotherapy. Predisposed patients may receive antibiotic-resistant staphylococci from hospital staff. The hands of medical personnel are one of the most common methods of transmission of the pathogen, but an airway transmission is also possible.

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

The genus Staphylococcus includes three species: golden (S. Aureus), epidermal (S. Epidermidis) and saprophytic (S. Saprophyticus). Each type of staphylococcus is divided into independent biologo-ecological types.

The type of Staphylococcus aureus includes 6 biovars (A, B, C, etc.). Pathogenic for man and the main causative agent of diseases - type A, the other biotypes are pathogenic for animals and birds.

Staphylococcus produces toxins and enzymes (coagulase, hyaluronidase, fibrinolysin, lecithinase, etc.) that promote the spread of the pathogen in the tissues and cause disruption of the life of the cells of the macroorganism.

The pathogenesis of staphylococcal infection

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

With a reduced resistance of the organism to pathogenic staphylococcus under the influence of the damaging effect of its toxins and enzymes, the pathogen and its toxins penetrate from the focus of infection into the blood. There comes bacteremia, intoxication develops. In generalized staphylococcal infection, various organs and tissues can be affected (skin, lungs, digestive tract, bone system, etc.). As a result of generalization, it is possible to develop septicemia, septicopyemia, especially in newborns and children of the first months of life.

In the pathogenesis of food poisoning, the bulk of infection is of major importance, with both enterotoxin and staphylococcus important. In the remnants of food, vomit masses and stools, patients usually discover pathogenic staphylococcus in huge quantities, sometimes in pure culture. However, the pathological process in food-borne disease is due mainly to the enterotoxin fed with food.