The bactericidal effect of dendritic copper microparticles, contained in an alginate matrix, on Escherichia coli.

Although the bactericidal effect of copper has been known for centuries, there is a current resurgence of interest in the use of this element as an antimicrobial agent. During this study the use of dendritic copper microparticles embedded in an alginate matrix as a rapid method for the deactivation of Escherichia coli ATCC 11775 was investigated. The copper/alginate produced a decrease in the minimum inhibitory concentration from free copper powder dispersed in the media from 0.25 to 0.065 mg/ml. Beads loaded with 4% Cu deactivated 99.97% of bacteria after 90 minutes, compared to a 44.2% reduction in viability in the equivalent free copper powder treatment. There was no observed loss in the efficacy of this method with increasing bacterial loading up to 10(6) cells/ml, however only 88.2% of E. coli were deactivated after 90 minutes at a loading of 10(8) cells/ml. The efficacy of this method was highly dependent on the oxygen content of the media, with a 4.01% increase in viable bacteria observed under anoxic conditions compared to a >99% reduction in bacterial viability in oxygen tensions above 50% of saturation. Scanning electron micrographs (SEM) of the beads indicated that the dendritic copper particles sit as discrete clusters within a layered alginate matrix, and that the external surface of the beads has a scale-like appearance with dendritic copper particles extruding. E. coli cells visualised using SEM indicated a loss of cellular integrity upon Cu bead treatment with obvious visible blebbing. This study indicates the use of microscale dendritic particles of Cu embedded in an alginate matrix to effectively deactivate E. coli cells and opens the possibility of their application within effective water treatment processes, especially in high particulate waste streams where conventional methods, such as UV treatment or chlorination, are ineffective or inappropriate

A comparison between ultraviolet disinfection and copper alginate beads within a vortex bioreactor for the deactivation of bacteria in simulated waste streams with high levels of colour, humic acid and suspended solids.

We show in this study that the combination of a swirl flow reactor and an antimicrobial agent (in this case copper alginate beads) is a promising technique for the remediation of contaminated water in waste streams recalcitrant to UV-C treatment. This is demonstrated by comparing the viability of both common and UV-C resistant organisms in operating conditions where UV-C proves ineffective - notably high levels of solids and compounds which deflect UV-C. The swirl flow reactor is easy to construct from commonly available plumbing parts and may prove a versatile and powerful tool in waste water treatment in developing countries

The biocidal effect of differing Cu concentrations entrapped in alginate beads on <i>E. coli</i> ATCC 11775 over time.

<p>Black diamond = Plain alginate beads. White square = 1% Cu W:W. Black triangle = 2% Cu. Black cross = 3% Cu, Black dash = 4% Cu. Black circle = 4% copper powder not associated with alginate. Bars denote standard errors.</p

SEM of internal surface of alginate bead structure.

<p>A: Internal bead surface at x 750 magnification of dendritic copper particles visible, B: Internal bead surface at x 3300 times magnification of dendritic copper particle protruding from alginate matrix and C: A cross section of the Cu alginate bead.</p

The viability of <i>E. coli</i> ATCC 11775 during treatment with 4% Cu (in alginate beads) under anoxic conditions (DO<0.1 mg/l).

<p>The experiment was performed at 37°C, with a bacterial loading of 10⁶ cells/ml.</p

The UV-fluence response curves for <i>E. coli</i> ATCC 1775 (•); <i>Enterococcus faecalis</i> ATCC 19434 (□) and <i>Deinococcus radiodurans</i> ATCC 13939 (○).

<p>The UV-fluence response curves for <i>E. coli</i> ATCC 1775 (•); <i>Enterococcus faecalis</i> ATCC 19434 (□) and <i>Deinococcus radiodurans</i> ATCC 13939 (○).</p

The relationship between dissolved oxygen concentration and <i>E. coli</i> ATCC 11775 viability using 4% Cu in alginate beads.

<p>The experiment was performed over 90<b> </b>minutes at 37°C, with a bacterial loading of 10⁶ cells/ml. Bars denote standard errors.</p

SEM of <i>E. coli</i> cells A: before and B: 45 minutes post treatment with Cu-containing alginate beads.

<p><i>i</i> indicates disruption to cell membrane with associated loss in cellular integrity.</p