Nanoparticles with anti-biofilm activity have gained attention in the past decade as some can naturally kill bacteria (they are bactericidal) and a few also have biofilm-eradicating properties.
The unique properties of nanoparticles (NPs) distinguish them from their bulk chemical counterparts. One such property is their large surface area to volume ratio, which creates a higher number of functional sites and can enhance the influence of NPs on a given microorganism. Since the antibacterial properties of some NPs are mediated mainly by direct contact with the bacterial cell wall and do not require penetration, most bacterial antibiotic resistance mechanisms are not relevant when dealing with NPs. Therefore, NPs are less prone to induce bacterial resistance than traditional antibiotics. This favourable property has stimulated extensive research on the antibacterial effects of diverse NPs types, such as carbon-based materials (fullerenes and carbon nanotubes), dendrimers that provide cavities for other molecules, nanocomposites, natural NPs and metal-based NPs, including silver, gold, metal oxides (such as ZnO and CuO).
Due to their potent antimicrobial effects, silver compounds have been used since ancient times (Egyptians, Greeks, Romans) to prevent microbial infections associated for example to water consumption. Several studies have investigated the antimicrobial and anti-biofilm activity of silver nanoparticles (AgNPs) on Acinetobacter baumannii, Escherichia coli and Staphylococcus aureus biofilms and demonstrated that AgNPs are potent anti-biofilm agents. However, metal oxide NPs are more commonly used within industry. They include iron oxide (Fe3O4), titanium oxide (TiO2), zinc oxide (ZnO), copper oxide (CuO) and magnesium oxide (MgO). These NPs show antimicrobial properties and can be applied in diverse industrial environments. These organic and inorganic NPs can be modified with different atoms, materials or other NPs. The resulting nanocomposites can potentially exhibit improved or new properties that can be exploited for multifunctional applications. As such, these hybrid nanostructure systems represent an area of extensive research.
Another interesting approach consists in exploiting the effectiveness of different nanocomposite materials toward reducing bacterial adhesiveness. For example, sulfhydryl compounds such as cysteine, dithiothreitol or beta-mercaptoethanol were able to reduce aureus biofilm formation on polystyrene polymer by inhibiting extracellular matrix biosynthesis genes such as ica.
Researchers have also investigated polymeric nanomaterials with inherent anti-biofilm properties. These materials often work through electrostatic interactions with bacterial biofilms. Chitosan is a commonly used charged polymer that has high antibacterial activity. It can achieve >90% inhibition of both mono and polymicrobial biofilms (Tran et al., 2020).
Nanomaterials can also act as carriers of other biofilm-eradicating agents (Tran et al., 2020). One study demonstrated the potential for efficient bacterial suppression using broad host-range (or phages) attached to magnetic colloidal nanoparticle clusters (CNCs). The CNCs facilitated biofilm penetration under a relatively small magnetic field (Li et al., 2017) and, once within the biofilm, the attached phages were able to infect the bacteria and kill them. This conjugation approach enhances the delivery of phages (or other anti-biofilm agents) to relatively inaccessible locations within biofilms.
Further reading on nanoparticles
Li, L.L., Yu, P., Wang, X., Yu, S.S., Mathieu, J., Yu, H.Q. and Alvarez, P.J.J. (2017) ‘Enhanced biofilm penetration for microbial control by polyvalent phages conjugated with magnetic colloidal nanoparticle clusters (CNCs)’, Environmental Science: Nano, vol. 4, pp. 1817-26, https://doi.org/10.1039/C7EN00414A.
Mohanta, Y.K., Biswas, K., Jena, S.K., Hashem, A., Abd_Allah, E.F., and Mohanta, T.K. (2020) ‘Anti-biofilm and Antibacterial Activities of Silver Nanoparticles Synthesized by the Reducing Activity of Phytoconstituents Present in the Indian Medicinal Plants’, Frontiers in Microbiology, vol. 11, https://doi.org/10.3389/fmicb.2020.01143.
Tran, H.M., Tran, H., Booth, M.A., Fox, K.E., Nguyen, T.H., Tran, N. and Tran, P.A (2020) ‘Nanomaterials for Treating Bacterial Biofilms on Implantable Medical Devices’, Nanomaterials, vol. 10(11), https://doi.org/10.3390/nano10112253.