Wednesday 11 April 2012

To Use a Predator


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:

Corin Liddle said...

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.

Matt Amos said...

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).