Carbon nanotubes as anti-bacterial agents

Abstract

Multidrug-resistant bacterial infections that have evolved via natural selection have increased alarmingly at a global level. Thus, there is a strong need for the development of novel antibiotics for the treatment of these infections. Functionalized carbon nanotubes through their unique properties hold great promise in the fight against multidrug-resistant bacterial infections. This new family of nanovectors for therapeutic delivery proved to be innovative and efficient for the transport and cellular translocation of therapeutic molecules. The current review examines the latest progress in the antibacterial activity of carbon nanotubes and their composites.

Keywords: Antibacterial agents; Multi-walled carbon nanotubes; Single-walled carbon nanotubes.

Fig. 1

Fluorescent staining of E. coli–SWNT aggregates. a DAPI (blue, viable) and PI (red, nonviable) staining of bacteria with <5% metallic SWNTs. b DAPI and PI staining of bacteria with >95% metallic SWNTs. c PI staining of bacteria with <5% metallic SWNTs. d PI staining of bacteria with >95% metallic SWNTs Reprinted with permission from [63]. Copyright 2011 American Chemical Society

Fig. 2

a OD growth curves of Salmonella cells (8.0 × 10⁷ cfu/mL) that were treated with SWCNTs of different lengths at a concentration of 100 μg/mL for 1 h prior to their growth in brain heart infusion (BHI) broth. b The viable cell numbers in the control and the samples treated with SWCNTs of different lengths at the concentration of 100 μg/mL for 1 h Reprinted with permission from [64]. Copyright 2010 American Chemical Society

Fig. 3

a Cell viability measurements after incubation with different surfactant solutions. Surfactant solutions (10 mL) were incubated with 1 mL of different bacterial suspensions (106–107 cfu/mL) for 2 h at 37 °C (30 °C for B. subtilis), respectively. Survival rates were obtained by the colony forming count method. Error bars represent the standard deviation. b Death rates of bacteria after incubation with SWCNTs dispersed in three different solutions. A 10-mL portion of SWCNT dispersion (5 pg/mL) was incubated with 1 mL of different bacterial suspensions (106–107 cfu/mL) for 2 h at 250 rpm shaking speeds, and at 37 °C or 30 °C. c Fluorescence microscope images of bacteria: (1) E. coli in 0.9 wt% NaCl control solution without SWCNTs; (2) E. coli after incubation with SWCNTs dispersed in saline solution; (3) E. coli after incubation with SWCNTs dispersed in the mixture of 0.1 wt% Tween 20 and 0.9 wt% NaCl; (4) B. subtilis in control solution without SWCNTs; (5) B. subtilis after incubation with SWCNTs dispersed in saline solution; (6) B. subtilis after incubation with SWCNT dispersed in the Tween 20-saline solution Reprinted with permission from [68]. Copyright 2009 American Chemical Society

Fig. 4

Antibacterial activities of the CNTs are associated with their diameter-dependent piercing and length-dependent wrapping, which cause lysis and loss of bacterial membrane potential, inducing the release of intracellular components such as DNA and RNA and resulting in the complete destruction of the bacteria Reprinted with permission from [57]. Copyright 2013 American Chemical Society

Fig. 5

Schematic illustration of a polyamide membrane formed by covalent binding of cytotoxic single-walled carbon nanotubes. Reprinted with permission from [70]. Copyright 2011 American Chemical Society

Fig. 6

Schematic presentation of mechanism of action of SWCNTs–Ag and pSWCNTs–Ag. The results demonstrated that SWCNTs–Ag down-regulate some of the genes associated with metabolism and outer membrane integrity; however, they are still toxic to human cells at their bactericidal concentration (62.5 μg/mL). On the other hand, pegylation of SWCNTs–Ag (pSWCNTs–Ag) did not affect their antibacterial activity (62.5 μg/mL), but reduced their toxicity to human cells. In addition, pSWCNTs down-regulated the expression of genes associated with quorum sensing, biofilm formation and virulence in Salmonella Reprinted with permission from [56]. Copyright 2015 BioMed Central