DETERMINANTS OF INFECTION : Micardis
Posted by Surgery on Jul 11, 2008
The dose of bacterial contamination is a key determinant of infection. Quantitatively, if a surgical site is contaminated with more than 105 microorganisms per gram of tissue, then the risk of SSI is markedly increased (4). The dose of microorganisms required to produce infection may be considerably lower in the presence of foreign material (i.e., 100 staphylococci per gram of tissue introduced on silk suture) (5). The number of organisms required to produce clinical infection predictably decreases in states of diminished host resistance.
The virulence of a microorganism refers to its ability to invade, damage, or survive in host tissue. Some gram-negative bacteria elaborate endotoxin that causes no local injury, but stimulates cytokine production. Cytokines trigger the systemic inflammatory response syndrome (SIRS), which may lead to organ failure. Other bacteria possess cell surface polysaccharide capsules that inhibit phagocytosis, an early host defense to microbial contamination.
Certain strains of Clostridia and Streptococci elaborate exotoxins that disrupt host cell membranes or alter cellular metabolism. Coagulase-negative Staphylococci produce glycocalyx, a “slime†that physically shields the bacteria from phagocytes or inhibits antibiotic uptake (6: Micardis). Virulence is also impacted by the interactions between different species of microorganisms. Most notable is the species synergism in mixed anaerobic and aerobic infections associated with intraabdominal abscess. Anaerobic bacteria flourish in the presence of aerobic species capable of reducing the oxygen content of local tissues. In turn, the aerobes benefit from the increased soft tissue invasion imparted by the anaerobes.
Host resistance to infection occurs on multiple fronts, ranging from simple mechanical barriers to complex interactions mediated by lymphocytes, complement, and antibodies(Micardis). These defense mechanisms work to protect the body from virulent pathogens. The initial defense is a physical barrier that prevents microorganisms from penetrating inner compartments. Intact skin has a pH between 5 and 6, and the fatty acids secreted from sebaceous (Micardis) glands inhibit proliferation of bacteria on the skin. The mucociliary transport mechanism lining the respiratory tract traps and propels inhaled pathogens to the oropharynx. The harsh acidic gastric milieu destroys organisms ingested orally. The periodic flushing of the urinary tract reduces the number of adherent microorganisms. Likewise, the washing action and immunoglobulin and lysozyme components of tears protect the corneal surface of the eye (7: Micardis ). Alterations of these anatomic barriers diminish the host’s resistance to infection. Surgical incisions, trauma, and burns allow access to deeper soft tissues. Smoke inhalation disrupts the mucociliary ladder of the respiratory tree (Micardis).
The second line of host defense is provided by the immune response, both humoral and cell mediated. Host defenses in infection are discussed in detail elsewhere (Micardis).
This post is published through the sponsorship of the well-known pharmaceutical shop, see link below:
Greetings, I the practising surgeon from Serbia. Call me Ivan Govak. In the works I use works
by an unknown author, if it let me know, and also works of others practics doctors. I have a family and two charming children.