Bacterial skin and wound infection

BACTERIAL SKIN AND WOUND INFECTIONS

Definition

Wound can be defied as any interruption of continuity of external or internal surfaces caused by violence

Wounds may occur following: surgery, trauma or injections

Wound infections may occur mainly after surgical procedures

Wound sepsis is the result of cross infection from human sources and from other outside sources.

Bacteria associated with wound infections

Many bacteria are associated with wound infection.

The normal flora may also cause infection.

The most common bacteria of the skin are: staphylococci, and various streptococci, Sarcina spp, anaerobic Diphtheroids, gram negative rods and others

The nutrition is derived from 1. sweat, 2. aminoacids and peptides from the skin, 3. fatty acids from the sebaceous glands of the skin.

Factors Determining the Ecology of the Skin Bacteria

Four main factors determine the ecology of skin bacteria

1.           The climate: The temperature and humidity

2.           The effect of free fatty acids

3.           Other bacterial inhibitors

4.           Maintenance of the flora by products of skin secretions

Defence Against Infection

1.      Intact skin. Normal uninterrupted skin provides protection against invasion by bacteria

2.      Lysozyme in sweat: The enzyme lysozyme provides protection against gram positive bacteria by lysing the cell wall.

3.      Ig A antibodies in the sweat and secretions provide first line of defense against infection

4.      Inhibitors like unsaturated fatty acids provide protection against bacteria

5.      Bacteriocins produced by the normal flora prevent the establishment of other bacteria

Factors Responsible For Wound Infections

A.    Host Factors: T

he following factors help the organisms tosurvive and produce the infections

1.           Extremes of age

2.           Diabetes mellitus

3.           Steroid therapy

4.           Obesity

5.           Malnutrition

6.           Immunocompromised individual

7.           Presence of remote infection at the time of surgery

B.     Exogenous Factors

1.           Use of un sterile instruments

2.           Surgeons hands / from health workers

3.           Air / Hospital environments

C.    Endogenous Factors

1.           Wound contamination from the patient source: from the normal flora

2.           Wound penetrating through structures containing normal flora

3.           Surgical procedures involving mucous membranes harboring normal flora

4.   Patients carrying pathogens in their nose, throat, axilla etc.

Etiological agents

Ps.aeruginosa

Staph.aureus

Proteus spp

Member of enterobacteriaceae

Anaerobic organisms

Anaerobic cocci

Bacteroides

Post Operative Infections

Gas gangrene organisms

S.aureus

Cl.tetani

Route of entry

Wounds may occur following: surgery, trauma or injections. Wound infections may occur mainly after surgical procedures. Wound sepsis is the result of cross infection from human sources and from other outside sources.

Mechanisms of damage

1.           Organisms enter through the skin, multiply there and pro-duce the disease in the skin. For example, impetigo, abscess and cellu-litis are caused by Staphylococcus aureus and Streptococcus pyogenes. As soon as the organisms enter the skin they multiple and produce various toxins that kill the cells and produce cellulites. Further damage leads to necrosis and ulcer formation.

2.           Organisms multiply in the skin and produce disease in inter-nal organs. For example some group A streptococci multiply in the skin and produce disease known as acute glomerulo nephritis causing damage to the kidneys. Some times C.diphtheriae may multiply in the skin and affect the heart due to the toxin.

3.           Some times organism may multiply in the skin and produce the toxin which affect the CNS and the effects are seen. In the case of Clostridium tetani, convulsions and paralysis occur due to the pro-duction of a powerful toxin

Laboratory diagnosis

Pus and wound swabs are cultured for the aerobic and anaero-bic organisms and are identified using appropriate biochemical tests.