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wounds 35 . Wolcott and colleagues showed in 2008 that an
intensive biofilm-based wound-care strategy significantly
improved healing frequency. The findings demonstrate
that effectively targeting bacteria in chronic wounds is
an important component of transforming ‘non-healable’
wounds into healable wounds 37 .
The challenging biofilm
From the above studies it appears that biofilms are evident
in wounds. Biofilms were also addressed in the 2013
EWMA document “Antimicrobials and Non-healing
Wounds Evidence, controversies and suggestions”. The
conclusions in the document were that further studies
elucidating the precise role of biofilms are urgently needed
since the nature of biofilms make their study very difficult
and therefore their impact a little controversial.
Diagnosing biofilm infections is extremely difficul t38 , and
therefore evaluating the impact of biofilms and novel antibiofilm
treatments is equally difficult. The difficulties in
diagnosing biofilms are in large part due to their very small
size. A recent literature study showed that biofilms that
cause inflammation rarely grow to sizes larger than 100
μm 39 . When considering that the spatial distribution of
such small biofilms is highly heterogeneous in a wound
(9,40 , one can imagine that the chance of finding and detecting
the bacteria are small. In addition to the low chance
of ‘hitting’ a biofilm when sampling from a wound, the
bacteria also need to be released from the matrix. In addition
to these difficulties, the method of detection might
also influence the diagnosis. Culturing bacteria has been
the gold standard, but many wound pathogens are very
difficult to culture (even if grown anaerobically) and persistent
cells from the biofilm might even be impossible to culture
41,42 . Molecular methods are generally more sensitive if
used with care; however, they also have their limitations 40
and the detection of 16s rRNA has also proved difficult in
non-growing biofilms (unpublished data).
Due to the above complications, in vitro biofilm studies
have widely been applied in the study of anti-biofilm treatment
strategies as an obvious alternative to clinical trials.
Such studies are much needed and yield much important
information if used with care. Until recently, such treatment
strategies have been tested on fast growing bacteria
in shaking cultures; these studies did not therefore involve
biofilm-growing bacteria. Now, the use of biofilm models
is becoming more common. The downside of in vitro
models is that it is impossible to mimic a clinical biofilm;
nevertheless, the lack or addition of host components such
as proteins and immune cells should always be considered.
Another challenge researchers should be aware of
is the false dogma stating that surface attachment per se
makes the biofilm tolerant. This is not true, because young
surface-attached biofilms still have high growth rates and
only a limited matrix shield and are therefore highly susceptible
to most antimicrobials. In our hands, biofilms
across species and models become tolerant between 20
hours and 48 hours after inoculation, but continue to
develop this tolerance 26 .
Rethinking diagnosis and treatment
Despite the above difficulties in the study of biofilms, it
appears that tolerant biofilms do impact wound healing
as they impact other chronic infections 35-37 . As suggested
for other biofilm infections, there is an urgent need to rethink
both the diagnosis and treatment strategies. Wound
expert Keith Cutting wrote a review on the challenge of
wound cleansing, in which he proposed that we need to
rethink our approach to wound cleansing: he suggested
more reflection on individual needs and thereby a reflection
of the need to use anti-biofilm treatment strategies 43 .
When studying the impact of biofilms and their treatment
in patients, it is important to combine several methods
of detection to avoid false negatives 38 . Studying the
healing of chronic wounds is further complicated by the
challenge and longevity of non-healing wounds.
As mentioned above, eradicating biofilm-forming
bacteria is almost impossible, and the best option is to
remove the infected area if possible 7 . Infected implants
and catheters can be removed, infected lungs of cystic
fibrosis patients can be explanted, and wounds can be
debrided 7,8,23,44 ; however, even in these cases, biofilms
seem to recur, and hence it is very important to find and
develop new strategies to combat bacteria in wounds.
Much research is ongoing within anti-biofilm strategies,
and a number of patents on single compounds are pending
(www.faqs.org/patents/).
In our hands, one of the most promising strategies
across all biofilm-related infections is biofilm disruption
combined with an antimicrobial agent. Biofilm disruption
and dispersal experiments suggest that biofilm tolerance
is readily reversible, whereas classic resistance due to mutations
is not 26 . Upon physical disruption the biofilm,
the bacteria inside the biofilm suddenly find themselves
outside of the protective matrix with fresh access to nutrients
and oxygen, which might induce growth. Thus, a
potential anti-biofilm strategy could be either mechanical
or enzymatic disruption of the wound biofilm. Several patent
applications are already pending on the anti-biofilm
effects of a biofilm destabilizing compound used together
with common antimicrobials in wound dressings (www.
faqs.org/patents/).
Furthermore, a good fraction of the latest wound biofilm
publications have been focused on novel treatment
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EWMA Journal 2014 vol 14 no 1