Chapter 24 Wound Infections Bio 261 Medgar Evers College, CUNY Prof. Santos

Classification of wounds Incisions: produced by knife or other sharp object Punctures: result from penetration by small sharp object Lacerations: occur when tissue is torn Contusions: produced by blow that crushes tissue Abrasions: occur when epidermis is scraped off Gunshot wounds: caused by bullets, other projectiles Burns: caused by heat, electricity, chemicals, radiation, or friction

Anatomy and Physiology 1- Tissue components exposed during a wound (break in skin or damage to skin) include collagen, fibronectin, fibrin, and fibrinogen. 2-They provide receptors to which potential pathogens can attach to. 3- Collagen is a fibrous material that is the main supportive protein in skin, tendons, scars, and other body components.

4- Fibronectin is a glycoprotein that both circulates the body and is a component of body tissue. In a tissue, it binds cells together. 5- Fibrinogen is a soluble blood protein that is converted to a fibrous material called fibrin after a wound occurs. This results in the formation of clots in the damaged vessels.

This stops the flow of blood as the first step in the repair process. 6- Wound healing begins with the outgrowth of connective tissue cells called fibroblasts and capillaries from the surface of wound to form nodular, red, translucent material called granulation tissue. Granulation tissue is bright red, differentiates into new capillaries and bleeds easily.

7- granulation tissue fills the void created by the wound, contracts, and is converted to collagen that composes the scar tissue and eventually covered by skin or mucous membrane.

Abscess formation An abscess is a localized collection of pus surrounded by a body tissue. It is composed of living and dead white blood cells, components of tissue breakdown, and infecting organisms. There are no blood vessels in an abscess since they have been pushed aside or destroyed. This results in poor delivery of medication or antimicrobial drugs to the area. An area of inflammation separates the abscess from normal tissue. This localizes the infection.

Microorganisms stop multiplying in an abscess so antimicrobial drugs such as penicillin has no effect. The chemical nature of pus interferes with antimicrobial drugs. An abscess must burst to surface or be drained surgically in order to effect a cure.

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microorganisms Epidermis Dermis Capillary Neutrophils 1 Microorganisms enter the tissue from a wound or from the bloodstream. 2 Blood vessels dilate, and leukocytes migrate to the area of the developing infection. Pus Blood clots Blood clots 3 Pus forms and an abscess develops; clotting occurs in adjacent blood vessels. 4 Buildup of pressure causes the abscess to expand in the direction of least resistance; if it reaches a body surface, it may rupture and discharge its contents. 10

Anaerobic wounds Allow anaerobic organisms such a Clostridium tetani to colonize and cause infection.

Staphylococcal wound infections 2 species of Staphylococci account for most human wound infections; Staphylococcus aureus and Staphylococcus epidermidis Symptoms include the discharge of pus, inflammatory reaction with swelling, redness, and pain Epidemiology; Staph is a normal habitant of the skin and nasal carriers have a greater chance of infection than noncarriers.

Old age, poor health, prolonged hospital stay, immuno-supression also contribute to the progression of disease. Treatment; cleaning and removing dirt, and anti Staph medication given to eliminate nasal carrier state or prior to surgery.

Group A Streptococcal flesh eaters Streptococcus pyogenes can colonize wounds and cause severe infections such as necrotizing fasciitis or flesh eating disease or worst streptococcal toxic shock. Symptoms; severe pain, swelling, fever and confusion. The overlying skin becomes stretched and discolored due to swelling. Shock and death will follow if treatment is not received shortly after infection.

Causative agent is S. pyogenes Causative agent is S. pyogenes. It is a beta hemolytic, aerotolerant, gram positive chain forming coccus with Lancefield group A cell wall polysaccharide. They possess at least 2 extracellular products; pyrogenic exotoxin A and exotoxin B.

Exotoxin A is a superantigen that causes shock and Exotoxin B is a protease that destroys tissue by breaking its proteins. Pathogenesis; S. pyogenes bind to fibronectins in tissue that help in colonization. They destroy Fascia or bands of fibrous tissues that underlie the skin and surround muscle and body organs. Intense swelling occurs due to fluid entering the area as a result of increased osmotic pressure from tissue breakdown into small molecules.

Prevention; urgent surgery is needed to relieve the pressure of the swollen tissue and remove dead tissue. Amputation is sometimes needed to rid patient of toxin.

Pseudomonas aeruginosa infections Agent of infection: P. aeruginosa is aerobic, gram negative, rod shaped with a single flagellum. It produces 2 pigments that often color the area of infection green. Symptoms; green coloration, chills, fever, skin lesions, and shock. Prevention; carefully remove dead tissue from wound, clean area, application of antibacterial cream and antibiotics.

Anaerobic bacterial infections Disease Cause Symptoms treatment Tetanus or lockjaw Clostridium tetani *release of tatanospasmin, a toxin that acts against nerve cells Restlessness, irritability, difficult swallowing, muscle pain and spasm in jaw, abdomen, or entire body Tetanus antitoxin

Anaerobic bacterial infections Disease Cause Symptoms treatment Gas gangrene (clostridial myonecrosis) Clostridium perfringens *secretion of alpha toxin that kills wbc’s and tissues Severe pain, gas and fluid seep from wound, blackening of skin, shock and death follows! Clean wounded area, surgical removal of dirt and dead tissue, oxygen, antibiotics.

Anaerobic bacterial infections Disease Cause symptoms pathogenesis treatment Lumpy Jaw or actinomycosis Actinomyces israelii Chronic disease, painful swellings under the skin, involves face and neck, chest or in the genital tract of women. These swellings can open to release pus. Usually begins in mouth area and extends outward. Long treatment due to slow growth, a number of antibacterial medications can be given.

Bacterial bite wound infections Disease Cause Symptoms treatment Pasteurella multocida infections from dog, cat, monkey, human bite. Pasteurella multocida *gram – coccobacillus lives in mouth Spreading redness, tenderness, swelling, discharge of pus Treatment with penicillin is effective if given early

Bacterial bite infections Disease Cause Symptoms treatment Cat scratch disease Bartonella henselae Pimple appears at the bite, local lymph node enlargement, fever, and convulsions Avoid rough play with pet cat, flea control in cats, apply antiseptic, and antimicrobial treatment

Bacterial bite infections Disease Cause Symptoms treatment Streptobacillary rat bite infection Streptobacillus moniliformis *some develop L- form variants which lack a cell wall Chills, fever, muscle aches, headache, vomiting, rash and pain in the large joints Penicillin and control rat population

Bacterial bite infections Disease Cause Symptoms treatment Human bite infection Mixed mouth flora including staph, anaerobic streptococcus Pain, swelling, drainage of foul smelling pus Avoid human altercations that might lead to biting.

Fungal wound infections Disease Cause Symptoms treatment Rose Gardener’s disease Sporothrix schenckii Painless, ulcerating nodules appearing in a linear fashion Protective clothing, amphotericin B or itraconazole