According to the Cambridge Dictionary, a wound is “a damaged area of the body, such as a cut or hole in the skin or flesh”. The wound is therefore an opening of the skin, possibly with some tissue damage, that the body urgently needs to repair, because
- the body may lose vital resources through the opening, e.g. blood, and this may affect the ability of the body to continue functioning; and
- microbes such as bacteria and fungi may enter the body through the opening to inflict damage first in the wound and, if they succeed to enter the blood, to be carried around and cause harm in the entire body.
These microbes will seek to multiply inside the body and, for this process, they will use the body’s nutrients and often use and kill the cells of the body. The impact and weakening may be so severe, that the body is unable to function and the individual dies.
Dr. Karl Klose from The University of Texas at San Antonio explains how bacteria are an integral part of us and our environment and how we usually live in synergy with them. He also explains about the defence mechanisms of bacteria as well as about antibiotics and antibiotic resistance.
It is clear that wounds that face the body's surface are and will always be constantly exposed to bacteria. Therefore, it is also evident that the simple killing of all the bacteria, as is the intention of antibiotics and antiseptics, is no feasible solution to wound infections. On the contrary, the synergy between the bacteria and the skin needs to be restored.
Microbes’ Weapons and Protective Armour
Bacteria and fungi have developed very effective “weaponry” to protect themselves as they typically live in spaces where everyone is fighting for an area to live and grow.
These can be divided into:
- Weapons - toxins and enzymes that are released to kill or inhibit the function of other microbes as well as of the immune cells of the body.
- Protective armour – biofilm, which is a viscous layer secreted as a shield or fortress to protect themselves against the environment, e.g. drought. However, it will also protect them against the immune system as the immune cells are unable to penetrate the biofilm.
The bacteria and the fungi need to find spaces and sources of food that allow them to grow and multiply in order to ensure the survival of the species and in this respect an animal or human body represents an ideal place as it is warm, moist and in itself an ideal food source. Many microbes have, therefore, developed strategies to circumvent the defence systems of the body. To give an example, Staphylococcus aureus excretes a toxin that, if the bacterium is present in high numbers, intoxicates the body’s own immune cells and trick them into attacking the cells of its own body instead of the bacterium, i.e. they are fooled into protecting the bacterium. The toxins secreted by bacteria and fungi can enter the blood and be circulated throughout the body (toxaemia) and may affect the vital organs leading to shock (sepsis) often with lethal consequences. Wounds are one of the main origins of septicaemia and consequently main causes of sepsis.
- Internal regions not in direct contact with the environment, e.g. the blood and brain: The immune system keeps these areas sterile, i.e. all microbes are removed.
- External areas in direct contact with the environment, e.g. the skin and gut: It is not possible for the immune system to keep these areas sterile. Instead, it works in synergy with selected microbes to protect our body against the microbes that can be dangerous to us.
- If microbes encounter an empty space, they will seek to colonise it.
- Some microbes are always dangerous to humans and need to be removed, e.g. Anthrax.
- Other microbes are only dangerous if they gain a dominant position, e.g. Staphylococcus aureus.
- microbes that are non-pathogenic (not intrinsically disease causing)
- a mix of many different species. These will keep each other at bay and, consequently, prevent anyone, benign in low numbers, suddenly becoming dominant and pathogenic (disease causing).
Wound healingThe natural wound healing process is normally divided into 3 phases:
- Inflammatory Phase (response to injury) - Immediate to 2-5 days
- Proliferative Phase (tissue regeneration) - 2 days to 3 weeks
- Maturation Phase (improving strength) - 3 weeks to 2 years
Factors influencing wound healing
Infection or critical colonisation
A wound with an out-of-control microbiome will not heal and it is therefore necessary to assist the wound in regaining control of the microbiome. However, the microbiome extends deep into the dermis (Nakatsuji et al. 2013) and data seem to indicate that different bacterial species have different preferences (Costello et al. 2009; Grice and Segre 2011; Pellegatta et al. 2016) with regard to which layers they prefer. This may explain why some wounds seem to have cleared an infection on the surface but still do not heal.
The older the wound, the wider and the deeper the infection will have had the time to spread. This process of spreading and becoming increasingly firmly embedded in the affected tissues can continue for years, leading to an extensive penumbra, i.e. an affected region around and underneath the actual wound. The longer the process has been on-going (months – year – several years), the more difficult it becomes to re-establish a microbiome that allows for healing to proceed and the longer the healing process will often take. The healing process, once it starts, is usually visible by regular deposits of mucky waste on the wound surface as this is the only place the body can dispose of the waste originating from tidying up the penumbral area. Finally, it is not unusual that old wounds ache when the restoration process is being undertaken.
Osteomyelitis (bone infection) can ensue as a result of an infection on top of a bone. Osteomyelitis is very difficult to treat and needs surgical intervention. If osteomyelitis has developed, the wound on top cannot heal. The microbes causing the infection in the bone generate waste and this must be able drain to the surface. The wound serves as the area of waste disposal.
The presence of underlying diseases in the tissue can cause the emergence of a wound, e.g. cancers, or impair healing and, consequently, lead to a wound growing in size or severity, as e.g. can be the case in diabetes.