There have been various attempts to develop methods
for reducing biofilms and in recent years there has been particular interest in
the use of biological agents for control, including viruses and grazers.
However there has been little research on the use of Bdellovibrio-and-like organisms (BALO), which prey on gram negative
bacteria and are ubiquitous in nature. This study examines the ability of Bdellovibrio bacteriovorus (BB) to prey on biofilms using Escherichia coli and Pseudomonas
fluorescens in both static and flow
cell experiments.
A microtiter dish-based static assay was used to assess
the predation of BB on planktonic and biofilm E.coli. Crystal violet and viable cell counts were used to measure
the decrease in E.coli numbers. The
effects of BB on E.coli biofilms were
visualised using scanning electron microscopy (SEM). They also examined the
effects of BB predation on thicker biofilms using flow-cell-grown biofilms of E.coli and P.fluorsecens. They inoculated
the biofilms with a single 1ml (109 PFU) dose of BB using a continuous
flow cell system and Baclight live/dead stain to assess cell viability. The
structures of the biofilms were examined using phase contrast microscopy.
The static biofilm experiment showed with a titer of
102 PFU/well of BB there was a reduction of 90% after 24hrs which
remained constant for the duration of the experiment (72 h). High concentrations
of BB remained till the end of the experiment regardless of the loss of prey. In
the static planktonic experiment E.coli
were reduced to undetectable limits within 24 h which suggests that biofilm
formation does reduce predation. Similar results were observed in the flow cell
experiments. There was a ~5-log reduction in both biofilms after 48 h which
remained constant for the duration of the experiment and high numbers of BB
were detected at the end of the experiment. The phase contrast microscopy also
showed that the control biofilms produced mushroom like structures whereas the
treated bacteria produced monolayer biofilms.
BALO have great potential as biological agents to
control biofilms for many reasons. This study shows that they are able to
penetrate biofilms to at least 30 um, multiply naturally which allows a low
initial dose, remain for at least three days in biofilms and are specific to
bacteria. Additionally prey cells have not been shown in this study or others
to develop resistance however plastic responses have been observed which
usually stop the complete loss of prey cell populations. BB treated biofilms
were also much easier to clean after the experiments. The study does show they
have potential; however it would be interesting to see if they are still
effective in more complex biofilms and over longer periods of time.
A review of: Kadouri, D. and O’Toole, G.A. (2005)
Susceptibility of biofilms to Bdellovibrio
bacteriovorus attack. Society. 71(7), 4044-4051.
2 comments:
Interesting, I was trying to imagine how such a biological control would be applied,I guess you could paint the culture onto a biofilm. To package and administer such products on a commercial basis must be tricky.
I think this is one of very few studies looking at BALOs in biofilms, so they re not really looking at whether they could be used to control them or not. Its more about examining the impacts they have on biofilms and that the results could give them potential as biological controls. I dont really know what the best method of applying them would be but trying to produce them on a commercial scale as you said could be difficult especially as studies have had difficulties producing mass cultures. I think BALOs have a lot of potential uses but its hard to really tell since there hardly any studies on them (other than medical).
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