Bacteriology of wound
Bacteria are inevitably present in wounds. This is natural colonisation.
The distinction between critical colonisation and infection depends on the quantity of bacteria and the response of the body.
Critical colonisation
What is critical colonisation?
Colonisation is caused by the presence of bacteria within the wound, without this leading to an inflammatory response. Most colonisation of acute wounds is composed of streptococci and staphylococci which are already present on normal healthy skin. The bacterial population in chronic wounds is much more varied. It is composed of the commensal skin bacteria such as Staphylococcus (S. aureus, coagulase-negative staphylococci), corynebacteria, α-haemolytic streptococci. After microorganisms have multiplied within the wound and bonded to epithelial cells, an equilibrium is set up between the patient and his/her microbial flora.
Microorganisms remain on the surface of the wound and form a biofilm.
Quantitatively, normal colonisation is defined by a bacterial count of 105 /mm3. If the number of bacteria exceeds this figure, it is referred to as critical colonisation, even if there is no obvious inflammation. The presence of large quantities of bacteria hinders the natural healing process and delays it.
Since routine examinations do not include bacteriological sampling, the main signs which suggestbacterial colonisation are: the abundance and thickening of foul-smelling exudate, spontaneous pain, erythema around the lesion and oedema.
Infection
What is an infection?
The term infection is used when the presence of micro-organisms leads to a local, regional or general inflammatory response with clinical symptoms.
This is due to several factors
- Large quantities of microorganisms present
- Bacterial virulen
- Reduction in the patient’s immune defence mechanism
The local or systemic clinical symptoms will be obvious
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Which microorganisms are involved in the infection process?
Normally, microorganisms are defined by using a staining technique based on the membrane properties and the wall of the bacteria. Gram staining is a determining factor in bacterial taxonomy (classification). Gram-positive bacteria appear mauve and Gram-negative bacteria appear pink under the microscope.
The most common microorganisms in the GRAM + family are
- Staphylococcus aureus
- Streptococcus pyogens
- Enterococcus faecalis
The most common microorganisms in the GRAM - family are:
- Enterobacteria
- Pseudomonas aeruginosa
Candida albicans (yeast) is a completely separate infectious agent that is less frequently present in the wound.
Consequences of infection
An infection is characterised by local, regional and systemic clinical symptoms. They can eventually lead to the exposure of underlying anatomical structures such as ligaments or bones. Systemic symptoms include fever, fatigue, regional lymphangitis and abnormal laboratory findings (Sedimentation Rate and C-Reactive protein)
In diabetic foot ulcers, it is essential to ensure that the infection has not spread to the bone and consequently an X-ray or MRI scan will be necessary.
Normal bacterial colonisation does not require specific therapeutic procedure, while an infection will require the use of local or general (atopic or systemic) antibacterial treatments.
Role of silver
The antibacterial properties of silver have been widely recognized and exploited since ancient times. Modern medicine has made great use of silver in the form of silver nitrate sulfadiazine, in the prevention and treatment of infection in both acute and chronic wounds.
In the case of chronic wounds, secondary infection can delay healing as a result of local inflammatory reaction and it is in this context that silver salts are used in the treatment of wounds with a high bacterial colonisation due to their antibacterial and local anti-inflammatory properties.
In recent years, numerous protocols have been recommended to treat acute or chronic wounds, in the form of creams or dressings containing silver.
The silver ion has a broad spectrum of activity that covers almost all microorganisms associated with the colonisation of chronic wounds. It acts on numerous targets and is bactericidal at very low concentrations, thereby minimising the potential risk of resistance.
Finally, Silver has no cytotoxicity that hinders the healing process
Ag+ MECHANISM OF ACTION - Ag+ ANTIBACTERIAL ION
Silver is only active in its Ag+ ionic form. It is quite alone in this classification since it is neither a genuinely antiseptic nor a genuinely antibiotic treatment and for this reason it is classified as an antibacterial agent.
Several characteristics of the Ag+ ion are specific in making the emergence of resistant strains difficult:
- bactericidal action of the Ag+ ion
- many actions targeted at the bacteria
- inhibits the bacterial DNA replication process
- reduces the wall strength
- increases the permeability of the bacterial cytoplasmic membrane
- inhibits the respiratory enzymes causing asphyxia of the bacteria
SIDE EFFECTS OF SILVER
Argyria
Local = hyperpigmentation
The reported cases indicate that a large quantity of Silver needs to be absorbed through the skin. Hyperpigmentation is due to deposition of Silver, usually characterised by a slate grey colour of the skin.
Systemic
The systemic effect is rare, but one significant systemic occurance should be noted: argyria (severe burn victims, infants).
RESISTANCE TO Ag+
To date, there have been no documented cases of resistance to silver ions.
