Antimicrobial applications of nanotechnology: methods and literature

Abstract

The need for novel antibiotics comes from the relatively high incidence of bacterial infection and the growing resistance of bacteria to conventional antibiotics. Consequently, new methods for reducing bacteria activity (and associated infections) are badly needed. Nanotechnology, the use of materials with dimensions on the atomic or molecular scale, has become increasingly utilized for medical applications and is of great interest as an approach to killing or reducing the activity of numerous microorganisms. While some natural antibacterial materials, such as zinc and silver, possess greater antibacterial properties as particle size is reduced into the nanometer regime (due to the increased surface to volume ratio of a given mass of particles), the physical structure of a nanoparticle itself and the way in which it interacts with and penetrates into bacteria appears to also provide unique bactericidal mechanisms. A variety of techniques to evaluate bacteria viability, each with unique advantages and disadvantages, has been established and must be understood in order to determine the effectiveness of nanoparticles (diameter ≤ 100 nm) as antimicrobial agents. In addition to addressing those techniques, a review of select literature and a summary of bacteriostatic and bactericidal mechanisms are covered in this manuscript.

Keywords: antibacterial; bacteria; biofilm; nanomaterial; nanoparticle; nanotechnology.

Figure 1

Zinc oxide (ZnO) nanoparticles (A), Escherichia coli bacteria prior to exposure to ZnO nanoparticles (B), and E. coli bacteria after exposure to ZnO nanoparticles (C). Membrane irregularities were observed in bacteria exposed to ZnO nanoparticles. With kind permission from Springer Science+Business Media: Journal of Nanoparticle Research. Investigation into the antibacterial behaviour of suspensions of ZnO nanoparticles (ZnO nanofluids). 9(3), 2007, page 483. Zhang L. Figure 2.

Figure 2

Transmission electron microscope images of silver nanoparticles used (A). Scanning electron microscope image of Escherichia coli control group (B) and E. coli exposed to 50 μg/mL of silver nanoparticles in lysogeny broth medium for 4 hours (C). Transmission electron microscope image of E. coli exposed to 50 μg/mL of silver nanoparticles in lysogeny broth medium for 1 hour at low magnification (D) and high magnification (E). Reprinted from Journal of Colloid and Interface Science, 275(1). Sondi I, Salopek-Sondi B. Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria. 177–182. Copyright © (2004), with permission from Elsevier.

Figure 3

Illustration comparing bacteria surface interactions with nanorough surfaces and conventional nanosmooth surfaces. Due to the high degree of roughness on nanomaterials, rigid bacteria cell membranes cannot lay flush against the material surface. This may inhibit the preliminary steps which lead to bacteria adhesion. As a result, bacteria activity on a nanomaterial surface may be reduced.

Figure 4

Atomic force microscopy images of particle compacts of microphase zinc oxide (ZnO) (A) and nanophase ZnO (B). Analysis indicated that compacts of nanophase ZnO had a 25% increase in surface area. Copyright © 2006, John Wiley and Sons. Adapted with permission from Colón G, Ward BC, Webster TJ. Increased osteoblast and decreased Staphylococcus epidermidis functions on nanophase ZnO and TiO2. J Biomed Mater Res A. 2006;78(3):595–604.

Figure 5

X-ray electron microscopy image of silver nanoparticles (A) and a particle size distribution histogram (B) of those particles. Higher magnification reveals polyhedral structure (C). Nondisruptive electron transmission microscopy reveals an 80–120 nm coating of silver nanoparticles on the surfaces of a polymer catheter (D).