Interaction of graphene family materials with Listeria monocytogenes and Salmonella enterica

Natalia Kurantowicz 2 Ewa Sawosz 2 Sawomir Jaworski 2 Marta Kutwin 2 Barbara Strojny 2 Mateusz Wierzbicki 2 Jacek Szeliga 2 Anna Hotowy 2 Ludwika Lipiska 1 Rafa Koziski 1 Joanna Jagieo 1 Andr Chwalibog 0 0 Department of Veterinary Clinical and Animal Sciences, University of Copenhagen , Groennegaardsvej 3, 1870 Frdereiksberg C, Copenhagen , Denmark 1 Institute of Electronic Materials Technology , Wolczynska 133, 01-919 2 Department of Animal Nutrition and Biotechnology, Faculty of Animal Science, Warsaw University of Life Sciences , Ciszewskiego 8, 02-786 Warsaw , Poland 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 g/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 g/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. - Background Due to the development of antibiotic-resistant bacterial strains, there is an increasing need to evaluate and develop alternative methods for antibacterial treatment [1-5]. It has been reported that carbon (i.e., nanotubes and fullerenes) and diamond nanoparticles possess antimicrobial properties [6,7]. Recently, it has also been demonstrated that a new allotrope of carbon, graphene, has antibacterial activity [8]. This activity has also been reported to be more effective than some currently used therapeutic antibiotics [5]. Graphene is a two-dimensional monolayer of carbon atoms which are tightly packed into a flat hexagonal structure, similar to that of a honeycomb lattice [9]. Graphene is regarded as the thinnest material in the world as it is only one carbon atom thick [10], although its surface area may be up to 1 cm2 [11]. The ratio of its thickness to surface area is exceptional when compared to other nanoparticles. Moreover, graphene is considered to be an elementary building block for all sp2-hybridized carbon allotropes [12]. Defect-free pristine graphene (pG) does not have any dangling bonds on its surface [13]. In contrast, the edges of pG consist of a line of atoms with dangling bonds, differing from the surface in terms of electronic, chemical, and magnetic properties. These unstable dangling bonds are subjected to chemical functionalization under ambient conditions [14]. As a consequence, the nature of the interactions of biological molecules and/or cells with pG is likely to depend on the site of interaction: the surface or edges. Previous findings indicated that glioblastoma cells had a strong affinity for, and adhered to, the surface of pG flakes, rather than the edges [15]. pG however differs both physically and chemically from graphene oxide (GO) and reduced graphene oxide (rGO). pG is manufactured by the exfoliation of graphite, whereas GO is obtained by the oxidation of graphite in the presence of strong acids and oxidants. Subsequent reduction of GO is used to generate rGO [16]. GO differs significantly from other graphene family materials (GFM) due to the disruption of its sp2 bonding network. GO also possesses oxygen as a significant chemical component (approximately 30% (w/v)) in the form of oxide functional groups, which can be mainly classed as either alcohols or epoxides [17]. This results in GO having partial hydrophilic properties, unlike pG [8,18]. rGO is quite different chemically from its GO precursor, instead being more similar to pG [17] due to its hydrophobic -bond graphene domains [8,18]. GFM have high thermal stability and mechanical strength, with relatively good biocompatibility with humans. These features make them very robust, useful, and multifunctional materials, particularly in light of the increasing evidence of their antibacterial properties [5]. Hu et al. [19] observed that GO had a detrimental effect on Escherichia coli, due to decreased bacterial production of ATP. Reduction of GO to rGO, however, resulted in slightly lower antibacterial activity relative to GO, as well as significantly increased the cytotoxicity. Liu et al. [20] explained the antibacterial effect of GO against E. coli by the induction of oxidative stress. However, it has also been demonstrated that GO had n (...truncated)