Abstract
High resistance of biofilms for chemical challenges is a serious industrial and medical problem. In this work a gradient of surface covered with biofilm has been produced and correlated to the effectiveness of different commercially available oxidative biocides. The results for thin Escherichia coli biofilms grown in rich media supplemented with glucose or lactose on glass or poly methyl methacrylate surfaces indicate that the effectiveness of hydrogen peroxide or chlorine dioxide and quaternary ammonium compounds is inversely proportional to the fraction of the surface covered with the biofilm. In areas where biofilm covered more than 90% of the available surface the biocide treatment was inefficient after 60 min of incubation. The combined effect of oxidant and surfactant increased the effectiveness of the biocide. On the other hand, the increased biofilm viscoelasticity reduced biocide effectiveness. The results emphasize differential biocide effectiveness depending on the fraction of the attached bacterial cells. The results suggest that biofilm biocide resistance is an acquired property that increases with biofilm maturation. The more dense sessile structures present lower log reductions compared to less dense ones.
Highlights
High resistance of biofilms for chemical challenges is a serious industrial and medical problem (Parsek and Fuqua, 2004)
In this work the biocide effectiveness was correlated to the surface area covered by E. coli biofilms
The obtained results imply a strong anti-correlation between the effectiveness of the biocide and the fraction of surface covered with the biofilm
Summary
High resistance of biofilms for chemical challenges is a serious industrial and medical problem (Parsek and Fuqua, 2004). There are multiple mechanisms of bacterial resistance which vary with the bacteria present in the biofilm and the drug or biocide being applied (Videla, 2002). These mechanisms include physical or chemical reaction–diffusion barriers to antimicrobial penetration into the biofilm, slow growth of the biofilm cells due to nutrient limitation, activation of the general stress response, and the emergence of a biofilm-specific phenotype (Mah and O’Toole, 2001; Stewart, 2002). It is generally assumed that biocide effectiveness in biofilms is approximately three orders of magnitude lower compared to bacterial suspensions (Mah and O’Toole, 2001). The effect of surface coverage heterogeneity in biofilms on biocide effectiveness has not been systematically studied yet
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