Download Biofilms- 11 Frequently Asked Questions

Biofilms - 12 Frequently Asked Questions
By Val Edwards-Jones, Gregory S Schultz and Jude Douglass
Q. Why is debridement a useful way of removing a biofilm?
Microorganisms growing within biofilms are usually resistant to the actions of most exogenous and
endogenous removal mechanisms because of protection conferred by a number of factors. The
exopolysaccharide matrix provides a physical barrier to phagocytosis and intracellular killing
mechanisms, to some antiseptics and antimicrobials. The reduced metabolism of bacteria within a
biofilm also renders them less susceptible to the action of antibiotics which tend to target rapidly
metabolizing organisms and this can be up to 1000 fold higher than free living bacteria. Currently,
physical removal through some form of debridement reduces numbers of bacteria and disrupts the
integrity of the matrix.
Q. Is debridement with maggots an effective way to remove biofilm in patients who can not tolerate
sharp debridement?
Early research suggests that the secretions from maggots may be effective against biofilms of S
aureus and P aeruginosa.(van der Plas et al 2007)
Q. What is wrong with the term “critical colonisation”?
The problem with this term is that it conveys no sense of urgency and can lead to complacency in
managing wounds. The term “Critical colonisation” is usually applied to wounds that are not healing
and known to be colonised by multiple species of bacteria. This term gives the impression that the
wound is in a state of “sub-infection”.
In fact, the reason the wound is not healing is most likely due to infection with a biofilm. Therefore
these wounds should be thought of as “infected” and should be managed as such.
Q. If it is impossible to see a biofilm in a wound, how do we know that at least 60% of chronic
wounds are colonised with biofilm?
The presence of biofilm in wounds can be confirmed through microscopic techniques such as
electron microscopy. However, these techniques are expensive, time-consuming and not readily
available for routine examination of chronic wounds. Therefore it is wise to assume that the majority
of chronic wounds are likely to be colonised with biofilm, and to take appropriate action. Some
sources claim that the figure is even higher than 60% and that as many as 80% of wounds could be
affected with biofilm.
Biofilms FAQs
Edwards-Jones, Schultz and Douglass, 2009
Q. Is slough an indicator of biofilm?
Research is still on-going into the precise nature and the effects of biofilms, but if you see slough in a
wound there is a good chance that it is due to the presence of biofilm.
Q. How do biofilms harm wounds and prevent them healing?
There are a number of factors. One of the most important is that biofilms release antigens, as do all
bacteria, which stimulates the production of antibodies. The antibodies, however, are incapable of
penetrating the exopolysaccharide shield and instead, cause damage to surrounding tissue. Biofilms
are also inflammatory, and constantly shed bacteria onto the wound, causing inflammation and
tissue damage through the release of proteases and reactive oxygen species (ROS).
Q. Why is the difference between biofilm and planktonic bacteria?
Bacteria present in biofilms are known as ‘sessile’ bacteria and are attached to a surface usually
encompassed by extracellular matrix. Biofilms can be made by single bacterial species
(e.g.Staphylococcus epidermidis causing biofilms on intravenous catheters) or multi species of
bacteria (seen in chronic wounds). Bacteria found within biofilms are difficult to remove and are
resistant to physical and chemical treatments.
Planktonic bacteria are free living bacterial cells released from the biofilm. They are ore susceptible
to antimicrobial agents and – if indicated – with topical antibiotics.
The only current treatment for biofilm that can be used with a high degree of confidence is removal
through physical debridement. Results published so far for silver dressings are mixed and suggest
they may cause disruption of the integrity of a biofilm. Results for iodine dressings are more
promising but have not been thoroughly validated.
Q. What dressings would you put on a wound once it has been cleared of biofilm?
Once the wound has been thoroughly debrided, you should use whatever dressing is appropriate for
the wound type and location, and the patient. In addition, it is advisable to use antimicrobials,
antiseptics or antibiotics depending upon the immune status of the patient and to hinder reformation of the biofilm. Once the colony has been disrupted through debridement, any bacteria
remaining in the wound will be susceptible to these therapies.
Biofilms FAQs
Edwards-Jones, Schultz and Douglass, 2009
Q. How long does it take for a biofilm to form after wounding?
As with any infection, this is highly dependent on many factors, including the type of organism, the
nature of the wound, and the general health of the patient. However, it is known that the process of
forming a biofilm can take as little as a few hours. The longer a wound is left exposed or untreated
after injury (including the “injury” of debridement) the more likely it is that a biofilm will form.
Q. Are there any biofilms that are not harmful?
Although many biofilms are harmful, there are some that have benefits. For example, certain
biofilms self-purify streams and rivers, and other are used in the treatment of waste and pollution
and for the generation of electricity. Within the body, many parts of the mucosa – such as in the
vagina and gut – are protected by biofilms formed from normal endogenous flora. It has also been
speculated that normal bacterial flora in biofilm form may help to prevent colonization of a wound
by exogenous organisms. This is a field of study that is receiving increased attention.
Q. How are wound swabs processed in the microbiology laboratory?
Traditionally, most sampling techniques involve surface swabbing of the wound and the
microorganisms picked up on the swab are merely a representation of those present in a wound.
They are inoculated onto a variety of different culture media and incubated for 24-48hrs in different
physical conditions (ncluding in oxygen (Aerobic) and in the absence of oxygen (anaerobic). This
allows growth of the predominant common pathogens. Those organisms known to cause infection
are reported with antibiotic susceptibility tests for the clinician. Other microorgansims are
mentioned if thought to be relevant.
Q. Why can biofilms not be detected easily in lab cultures?
1. Bacteria growing within a biofilm are very adherent to the surface and may not be removed
during sampling. Even if bacteria within a biofilm are captured by the sampling technique, reports
from clinical microbiology labs can only provide an indication of the predominant bacteria in a
wound and there are no current techniques available that will help the microbiologist decide which
bacteria, other than known common pathogens, that are causing the problem.
2. Traditional laboratory microbiology culturing techniques only “detect” (propagate) planktonic
bacteria and do not successfully culture bacteria in biofilms because special techniques must be
employed to break down the biofilm colonies into very small clusters containing only a few bacteria,
which will then grow under typical culturing conditions on nutrient agar plates or in nutrient broth.
Therefore, even if biofilm colonies are captured by the sampling technique, reports from clinical
microbiology labs do not provide meaningful information about biofilm bacteria in a wound.
Biofilms FAQs
Edwards-Jones, Schultz and Douglass, 2009
Biofilms FAQs
Edwards-Jones, Schultz and Douglass, 2009