Biocide effectiveness on biofilms is thought to be approximately three orders of magnitude lower compared to bacterial suspensions. However, this might be misleading as biofilms vary in thickness and composition, so biocides might work better in some areas than others.
Oxidative biocides are often used in industry in control of biofilms. They are proposed to have multiple targets within a cell which include peroxidation and disruption of membrane layers, oxidation of thiol groups, enzyme inhibition, oxidation of nucleosides, impaired energy production, disruption of protein synthesis and, ultimately, cell death.
Often used biocides such as H2O2 and ClO2 that involve free radical formation can change amino acids, peptides, and proteins through hydrogen abstraction, electron transfer (oxidation or reduction), addition, fragmentation and rearrangement, dimerization, disproportionation, and substitution (concerted addition and elimination). H2O2, per se, is considered a weak oxidant agent. However, it can easily cross the cellular membrane and reacts with transition metals, generating a highly reactive OH⋅ that may oxidize and fragment the protein or DNA backbone. On the other hand, the primary mechanism for inactivation of the Escherichia coli with ClO2 is disruption of the protein synthesis pathway by inhibition of enzymes or interference with nucleic acid–amino acid complexes.
Surfactants may be added to oxidizing agents to improve their antimicrobial effectiveness. Among them, cationic surfactants such as quaternary ammonium compounds (e.g., CTAB) are frequently utilised for disinfection and sanitation purposes in a variety of fields, such as hospitals, food manufacturing, and pharmaceutical industry. Cationic surfactants disrupt cell membrane, inhibits the activity of Mn-SOD and SoxS, cause leakage of intracellular K+ and other cell components, induce cell autolysis, and inhibit respiration.
Further Reading on biocides and biofilms
Bas, S., Kramer, M., & Stopar, D. (2017). Biofilm Surface Density Determines Biocide Effectiveness. Frontiers in microbiology, 8, 2443. https://doi.org/10.3389/fmicb.2017.02443.
(2011) Resistance of bacterial biofilms to disinfectants: a review, Biofouling, 27:9, 1017-1032, DOI: 10.1080/08927014.2011.626899.
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