Wound Abscesses

1. An abscess is composed of a collection of pus, which is composed of leukocytes, components of tissue breakdown, and infecting organisms.

2. Abscess formation localizes an infection within tissue to prevent its spread; inflammatory cells and clotted blood vessels separate the abscesses from normal tissue. (Figure 27.2)

712 Chapter 27 Wound Infections Anaerobic Wounds

1. Anaerobic conditions are likely to occur in wounds containing dead tissue or foreign material, and those with a narrow opening to the air.

2. Anaerobic conditions permit infection by particularly dangerous pathogens.

27.2 Common Bacterial Wound Infections (Table 27.2)

1. Possible consequences of wound infections include delayed healing, abscess formation, and extension of infection or toxins into adjacent tissue or the blood stream.

2. Infections can cause surgical wounds to split open, and they can spread to create biofilms on artificial devices.

Staphylococcal Wound Infections (Figures 27.3,27.4)

1. Staphylococci are the leading cause of wound infections, both surgical and accidental; Staphylococcus aureus and S. epidermidis, are the most common wound-infecting species.

2. Staphylococcus aureus possesses many virulence factors; occasional strains release a toxin that causes toxic shock syndrome (Table 27.1)

3. Staphylococcus epidermidis is less virulent but can form biofilms on blood vessel catheters and other devices.

Group A Streptococcal "Flesh Eaters"

1. Streptococcus pyogenes (Group A, ^-hemolytic streptococcus) causes strep throat, scarlet fever, wound infections, and other conditions.

2. Necrotizing fasciitis-causing strains produce exotoxin B, a protease thought to be responsible for the tissue destruction.

Pseudomonas aeruginosa Infections

1. Pseudomonas aeruginosa, an aerobic Gram-negative rod with a single polar flagellum, is an opportunistic pathogen widespread in the environment, and a cause of both nosocomial infections and those acquired outside the hospital.

2. Production of two pigments by the bacterium often colors infected wounds green. (Figure 27.6)

3. Toxin A of P. aeruginosa has a mode of action identical to diphtheria toxin, but is it antigenically distinct and attaches to different cells.

27.3 Diseases Due to Anaerobic Bacterial Wound Infections

"Lockjaw" (Tetanus) (Table 27.4)

1. The characteristic symptom of tetanus is sustained, painful, cramplike spasms of one or more muscles (Figure 27.7). The disease is often fatal.

2. Tetanus is caused by an exotoxin, tetanospasmin, produced by Clostridium tetani, a non-invasive, anaerobic Grampositive rod (Figure 27.8). The toxin renders the nerve cells that normally inhibit muscle contraction inactive by blocking release of their neurotransmitter. (Figures 27.9,27.10)

3. The spores of C. tetani are widespread in dust and dirt, and most wounds are probably contaminated with them.

4. Tetanus can be prevented by active immunization with toxoid (inactivated tetanospasmin), and maintaining immunity throughout life. Any wound, including surgeries, no matter how trivial, is an occasion to make sure immunizations are current. (Table 27.3)

Gas Gangrene (Clostridial Myonecrosis) (Table 27.5)

1. Usually caused by the anaerobe Clostridium perfringens, symptoms begin abruptly with pain, swelling, a thin brown bubbly discharge, and dark blue mottling of the tightly stretched overlying skin. (Figure 27.12)

2. The toxin causes tissue necrosis; hydrogen and carbon dioxide gases are produced from fermentation of amino acids and glycogen in the dead tissue.

3. There is no vaccine or toxoid. Prevention depends on prompt medical care of dirty wounds containing dead tissue. Treatment depends on urgent surgical removal of dead and infected tissue, and it may require amputation.

"Lumpy Jaw" (Actinomycosis) (Table 27.6)

1. Actinomycosis is a chronic, slowly progressive disease characterized by repeated swellings, discharge of pus, and scarring, usually of the face and neck. (Figure 27.13)

2. The causative agent is Actinomyces israelii, a member of the normal mouth, intestinal, and vaginal flora that enters tissues with wounds such as those with dental and intestinal surgery.

(Figure 27.14)

3. The organism is slow growing; treatment must be continued for weeks or months.

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