A review of: Wen J, Zhao K, Gu T, Raad II (2009) A green
biocide enhancer for treatment of sulphate-reducing bacteria (SRB) biofilms on
carbon steel surfaces using glutaraldehyde. International
Biodeterioration & Biodegradation, 63:
1102-11106.
Bacterial biofilms cause various problems such as fouling of
water cooling systems, medical infections, product contamination and
microbiologically influenced corrosion (MIC). MIC is responsible for billions
of dollars in losses each year for many industries and account for as much as
20% of all forms of corrosion, mostly caused by sulphate reducing bacteria
(SRB). Ethylenediaminetetraacetic acid (EDTA) is a chelating agent and is
widely used to eradicate biofilms on catheters when combined with antibiotics.
Previous experiments have also shown that EDTA combined with glutaraldehyde and
tetrakis hydroxymethyl phosphonium sulphate (THPS) can enhance the inhibition
of planktonic SRB growth. However, EDTA is not very biodegradable and so a
search for a more environmentally friendly chelator to replace EDTA has been
the impetus for the investigation by Wen et
al (2009).
Ethylenediaminedisuccinate (EDDS) and glutaraldehyde were
chosen for the experiment because EDDS is a popular biodegradable chelating
agent and glutaraldehyde is a widely used broad spectrum biocide. SRB Desulfovibrio desulfuricans subsp. aestuarii ATCC 14563 were grown to
approximately 4.3-5.1 x 105 cells ml-1 before being
placed in anaerobic vials containing different concentration of EDDS and
glutaraldehyde, and carbon steel coupons on which the biofilms would grow. The
coupons were observed using a SEM after eight days to determine whether SRB
biofilm formation was inhibited. The same experiment was conducted using
pre-existing SRB biofilms to determine the efficacy of EDDS and glutaraldehyde
in treating established biofilms. In addition, the effect of the biocide
enhancer and the biocide was also tested on the growth of planktonic forms of
the bacteria, enumerated using a haemocytometer and a light microscope.
Glutaraldehyde was shown to inhibit or delay SRB
proliferation after 8 days, with 30 ppm of glutaraldehyde combined with 2000
ppm of EDDS found to be highly effective in inhibiting planktonic and sessile
bacterial growth, as well as preventing biofilm formation on the coupons.
Biofilms protect bacteria from biocides like glutaraldehyde therefore its use
in conjunction with EDDS is far more effective than a higher concentration of
glutaraldehyde or EDDS alone. Trace metals are necessary for bacterial
metabolism and biofilm formation. Using chelating agents like EDDS sequester
trace metals, thus limiting bacterial adhesion and growth. Chelators can also
remove divalent cations from lipopolysaccharide, resulting in increased
permeability of bacterial cells. EDDS enhances the biocide activity of
glutaraldehyde by making it easier for glutaraldehyde to penetrate SRB biofilms
and the membranes of bacteria. Because the experiment used a relatively high
concentration of EDDS, a progression from the existing study would be to find
an optimal balance between chelator and biocide concentration for various
industrial applications.
2 comments:
Interesting, could such compounds be used to prevent Accelerated Low Water Corrosion?
Hey Corin,
I don't see why not. We had some experience using glutaraldehyde in electron microscopy and what it does is it cross links proteins in a cell because of terminal aldehyde groups. That must be the same process in its biocide activity. I do recall having to fill in COSHH forms because glutaraldehyde is quite harmful. I dont know what the implications of regular long term glutaraldehyde treatment but I'm sure the biodegradability of EDDS may be a suited for regular applications to prevent or limit biofilm formation by chelating metal ions necessary for bacterial growth.
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