We have been undertaking a study of biofilms in the food industry examining
the significance of biofilm formation in high-risk food processing
operations. It is apparent that biofilms form on food contact and
environmental surfaces and that these are not properly controlled by current
cleaning methods. The food industry does not fully recognise the importance
of surface attached populations and that the current definition for
'classic' biofilm is not of particular relevance to the industry where
populations are controlled to some extent by regular cleaning.
We need to discuss and arrive at a consensus definition relevant to the food
industry that incorporates the attachment and initial growth of cells. We
feel it should include:
1. The timescale for the physiological adaptation of sessile cells with
particular reference to dessication, biocide resistance and metabolic
activity.
2. The physiological activity of attached cells.
3. The number or density of cells required to constitute a biofilm - we
have evidence that swab recovery of 1x103 cfu/100cm3 from a surface
represents an attached population that is not easily eradicated by cleaning
procedures employed by the industry.
4. The potential for quorom sensing with reference to density of
attached population.
It is our opinion that if physiological adaptation and resistance to factors
such as detergent action, disinfection and dessication, occur shortly after
attachment to what would be a very small attached population, this should be
considered a biofilm. Thus a few adherent organisms do constitute a biofilm
or certainly has the potential form biofilm. The word film in this context
is a misnomer as it suggests that a continuous film is a prerequisite for a
sessile population to be called a biofilm. The dynamic nature of the
biofilm population in terms of attachment/detachment and growth is also
important.
We also feel that interfacial dimensions are not important in defining
biofilm as the population produces concentration gradients that will extend
way beyond the physical boundaries of the cells.
Biofilms are very diverse in structure etc. and will be different in every
environment in which they are being studied. We don't think one definition
can encompass all aspects of biofilms that have been observed (or that it
should). We all understand from generic definitions such as the one by
Characklis and Marshall eds. (Biofilms and interdisciplinary approach), the
basis of what is a biofilm. Each group will add different terms for the
biofilms that they are studying and these should be stated or defined by the
authors. As we are all familiar with each others work we do understand many
of the terms (streamers, voids, microcolonies etc.) that have been used to
describe biofilms. The primary/secondary/tertiary structures would be
useful descriptions, but for the high-risk food processing industry,
tertiary and maybe secondary structures would not occur because of the time
for more complex biofilms to develop between cleaning is not available.
This could be true for other terms too in that they will not all apply to
every biofilm studied.
Any comments would be very welcome.
Karen Elvers and Adrian Peters, UWIC, Cardiff, UK.
----------------------------------------
Dr. Karen T. Elvers
Food Safety Research Group
School of Applied Sciences
University of Wales Institute, Cardiff
Colchester Avenue
Cardiff
UK
CF23 9XR
Tel: 029 2041 6457
Fax: 029 2041 6941
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moderators comment: I an sorry that this message by mistake was not
forwarded immediately. It was posted July 30 1999.
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