Broad‐Spectrum Antibacterial Activity of Carbon Nanotubes to Human Gut Bacteria

Abstract

Carbon nanotubes (CNTs) hold promise in manufacturing, environmental, and biomedical applications, as well as food and agricultural industries. Previous observations have shown that CNTs have antimicrobial activity; however, the impact of CNTs to human gut microbes has not been investigated. Here, the antibacterial activity of CNTs against the microbes commonly encountered in the human digestion system--L. acidophilus, B. adolescentis, E. coli, E. faecalis, and S. aureus--are evaluated. The bacteria studied include pathogenic and non-pathogenic, gram-positive and negative, and both sphere and rod strains. In this study, CNTs, including single-walled CNTs (SWCNTs, 1-3 μm), short and long multi-walled CNTs (s-MWCNTs: 0.5-2 μm; l-MWCNTs: >50 μm), and functionalized multi-walled CNTs (hydroxyl- and carboxyl-modification, 0.5-2 μm), all have broad-spectrum antibacterial effects. Notably, CNTs may selectively lyse the walls and membranes of human gut microbes, depending on not only the length and surface functional groups of CNTs, but also the shapes of the bacteria. The mechanism of antibacterial activity is associated with their diameter-dependent piercing and length-dependent wrapping on the lysis of microbial walls and membranes, inducing release of intracellular components DNA and RNA and allowing a loss of bacterial membrane potential, demonstrating complete destruction of bacteria. Thin and rigid SWCNT show more effective wall/membrane piercing on spherical bacteria than MWCNTs. Long MWCNT may wrap around gut bacteria, increasing the area making contact with the bacterial wall. This work suggests that CNTs may be broad-spectrum and efficient antibacterial agents in the gut, and selective application of CNTs could reduce the potential hazard to probiotic bacteria.

Studies on Enhancement of Anti-microbial Activity of Pristine MWCNTs Against Pathogens

“…These negative values of zeta potential of MWCNT dispersions are in consonance with the previous published reports (38,39). Besides the cell-puncturing potential of MWCNTs, increased adhesion of these carbon-based nanoconstructs can be ascribed to the involvement of electrostatic factors too (40). The lower negative charge intensity on MWCNTs might have accounted for reduced repulsion by the negatively surfaced bacterial walls, resulting in relatively better adhesion of the MWCNTs and, thus, improved antibacterial efficacy.…”

Antimicrobial Nanoparticles: applications and mechanisms of action

“…CNTs with a length of more than 50 µm may wrap around the bacterial cell during the antimicrobial activity. 32 Long nanotube aggregates in liquid medium are known to be more bioactive and have potent antibiofilm activity, especially during the early phase of biofilm formation. 33 Carbon nanostructures may cause physical abrasions and structural damage to the bacterial cell walls and cell membranes.…”

Coculture with Low‐Dose SWCNT Attenuates Bacterial Invasion and Inflammation in Human Enterocyte‐like Caco‐2 Cells

“…Several studies including ours have reported that the CNTs possess effectively and broad-spectrally antibacterial activities with the mechanism of killing bacteria by the physical puncture of bacterial membranes, resulting in the damage of the integrity of cell wall and causing the cell death, which suggests for special benefi ts to prevent the growth of multi-drug-resistant microbes. [10][11][12] However, there is still much evidence that CNTs under uncontrolled conditions can cause health risks. A number of studies show that CNT exposure can induce oxidative stress, infl ammatory responses, DNA damage, and so forth.…”