Biofilms consists of a collective group of microorganisms that attach to each other or to a surface such as bacteria and the extracellular matrix secreted by the organisms1. A variety of pathogenic and problematic microorganisms may take shelter in these biofilms which are difficult to eradicate due to the inability of antimicrobial agents to penetrate the biofilm.
Biofilms in water distribution and storage systems can cause significant public health concerns due to the various pathogenic bacteria they house, as well as increase the economic costs of maintaining these systems as these biofilms also cause corrosion of pipes and other metal substrates they attach to1,2. Researchers from the Rice University’s Department of Civil and Environmental Engineering in collaboration with the University of Science and Technology of China’s Department of Chemistry have recently discovered that magnetic nanoparticle clusters – conjugated with polyvalent phages could enhance the biofilm penetration thereby suppressing the bacterial growth2.
Pedro J. J. Alvarez’s team utilized bacteriophages, which are the viruses that infect and multiply in bacteria, to effectively kill bacteria that usually resist chemical disinfection. Polyvalent phages that can attack multiple strains of bacteria were combined with nanoclusters that are modified with the coating of an amino group facilitating the attachment of bacteriophages’ head to the nanoclusters thereby leaving the infectious tails accessible to infect the bacterial biofilms2. This group of Researchers used a relatively weak magnetic field (660 gauss) to allow the phages bound to nanoclusters to adhere to the biofilm and destroy them2.
The Iron oxide (Fe3O4) colloidal nanocrystals (CNCs) were synthesize by a solvothermal reaction, which were then treated with tetraethyl orthosilicate (TEOS) to produce core shell Fe3O4-SiO2 CNCs3. Amino groups are then introduced onto the surface of Fe3O4-SiO2 CNCs by reacting with a modifying agent (3-aminopropyl) triethyl siloxane (APTES) and ammonium hydroxide (NH4OH) to form Fe3O4-SiO2-NH2 core shell CNCs. The Fe3O4-SiO2-NH2 core shell CNCs were further used to synthesize Fe3O4-SiO2-COOH core shell CNCs and the chitosan-coated Fe3O4 (CS- Fe3O4) CNCs2
Polyvalent phage PEL1 belonging to the Podoviridae family was immobilized and conjugated onto the Fe3O4 (CS- Fe3O4) CNCs in such a way that the CNCs are attached to the bacteriophages’ heads by a covalent bonding by forming amide linkages to form phage loaded magnetic nanocrystals (PEL1- CS- Fe3O4) 2. Because of this, the Researchers achieved a phage loading of (5.2 ± 0.7) × 103 centers of infection per 1 μg of chitosan-coated CNCs (CS-Fe3O4). Two strains of bacteria, Escherichia coli (C3000) and Pseudomonas aeruginosa (PA01) were used to test the plaque formation capabilities of chitosan-coated CNCs (CS-Fe3O4) 2.
The results showed that the plaque formation, which is measured as the area of petri dish infection, in case of both the bacterial strains was 99.1% in the phage loaded magnetic colloidal nanocrystals (PEL1- CS- Fe3O4) as compared to the 3.2% in the CNCs that were functionalized with the carboxyl groups (Fe3O4-SiO2-COOH) 2. Furthermore, the PEL1- CS- Fe3O4 was found to remove 88.7 ± 2.8% of the biofilm coverage area after 6 hours of treatment in the newly established biofilms formed from these two species on a glass surface2.
Even though the bacteria could develop resistance, the Authors believe that the ability of the phage enhanced CNCs to destroy the bacteria relatively quickly would make it relatively difficult2,3. The research team led by Pedro J. J. Alvarez is now working to develop phage “cocktails” that could combine different types of bacteriophages that can destroy several strains of bacteria while also incorporating antibiotics to prevent resistance.
This research puts forward a novel conjugation approach that combines the fields of nanotechnology and virology to destroy bacterial biofilms that are difficult to penetrate using antimicrobial agents. Due to the ability of these magnetic CNCs to penetrate the biofilms and destroy more than one strains of bacteria, this method could be especially useful in disinfecting water distribution and storage system.
The use of this conjugation approach could be extended to other applications of phages for microbial control by providing access to relatively inaccessible locations within the biofilms2.
- “Biofilms” – Nature.com
- “Enhanced biofilm penetration for microbial control by polyvcalent phages conjugated with magnetic colloidal nanoparticle clusters (CNCs)” L. Li, P. Yu, et al. Environmental Science: Nano. (2017). DOI: 10.1039/c7en00414A.