Interaction of graphene family materials with Listeria monocytogenes and Salmonella enterica

Abstract

Graphene family materials have unique properties, which make them valuable for a range of applications. The antibacterial properties of graphene have been reported; however, findings have been contradictory. This study reports on the antimicrobial proprieties of three different graphene materials (pristine graphene (pG), graphene oxide (GO), and reduced graphene oxide (rGO)) against the food-borne bacterial pathogens Listeria monocytogenes and Salmonella enterica. A high concentration (250 μg/mL) of all the analyzed graphenes completely inhibited the growth of both pathogens, despite their difference in bacterial cell wall structure. At a lower concentration (25 μg/mL), similar effects were only observed with GO, as growth inhibition decreased with pG and rGO at the lower concentration. Interaction of the nanoparticles with the pathogenic bacteria was found to differ depending on the form of graphene. Microscopic imaging demonstrated that bacteria were arranged at the edges of pG and rGO, while with GO, they adhered to the nanoparticle surface. GO was found to have the highest antibacterial activity.

Keywords: Bacteria growth; Graphene oxide; Listeria monocytogenes; Pristine graphene; Reduced graphene oxide; Salmonella enterica.

Figure 1

GFM were visualized using transmission electron microscopy (A-C), scanning electron microscopy (D-F), and a digital camera (G-I). Images of pristine graphene (A, D, G), graphene oxide (B, E, H), and reduced graphene oxide (C, F, I).

Figure 2

Size distribution of different graphene family materials, with intensity indicative of their concentration. Line color coding representative spectra: pristine graphene (blue), graphene oxide (green), and reduced graphene oxide (red). Triplicate measurements.

Figure 3

FTIR spectra of graphene family materials: pristine graphene (A), graphene oxide (B), and reduced graphene oxide (C).

Figure 4

Influence of pG, GO, and rGO on the growth of Listeria monocytogenes and Salmonella enterica at 25 and 250 μg/mL. Data presented are the average of triplicate determinations, with error bars representing mean standard error.

Figure 5

Visualization of the interaction of graphene family materials with Salmonella enterica using transmission electron microscopy. Pristine graphene (A, D, G), graphene oxide (B, E, H), and reduced graphene oxide (C, F, I). Black arrows indicate the graphene material and white arrows the bacterial cells.

Figure 6

Visualization of the interaction of graphene family materials with Listeria monocytogenes using transmission electron microscopy. Pristine graphene (A, D, G), graphene oxide (B, E, H), and reduced graphene oxide (C, F, I). Black arrows indicate the graphene material and white arrows the bacterial cells.

Figure 7

Effect of 25 μg/mL concentration of pG, GO, and rGO on the zeta potential of L . monocytogenes (L) and S . enterica (S). Data presented are the average of triplicate determinations, with error bars representing mean standard error.

Figure 8

Effect of pG, GO, and rGO at 25 and 250 μg/mL on the oxidation of the reduced DPPH radicals. Data presented are the average of triplicate determinations, with error bars representing mean standard error. Values with different superscripts are significantly different (P ≤ 0.05).

Figure 9

Three-step antimicrobial mechanism of graphene materials. 1. Initial bacteria cell deposition on graphene materials. 2. Membrane stress caused by direct contact with sharp edges. 3. Oxidative stress in the bacterial cytoplasm. The key difference between the chosen graphene materials is the bacterial cell deposition place. Individual bacterial cells interact with the sp³-hybridized oxidative functional group of the GO surface, while bacterial cells interact with the sharp edges of pG and rGO and form a rope-like structure.