doi:10.1038/nindia.2015.139 Published online 26 October 2015
Researchers have reported a simple approach to prevent hospital infections caused by superbugs that are resistant to antibiotics1.
"Our study shows a pathway to combat such pathogens simply using air, visible light and reduced graphene oxide (rGO)," Sabyasachi Sarkar, lead researcher and a chemist at the Indian Institute of Engineering Science and Technology, Shibpur, West Bengal, told Nature India.
"The rGO generates reactive oxygen species (ROS) under indoor light in air which readily kills Enterobacter species, a very difficult source of hospital pathogen," he said.
Enterobacter is a genus of gram-negative bacteria of the family Enterobacteriaceae, several strains of which are pathogenic and cause opportunistic infections in immunocompromised patients.
This approach could be useful to combat strains like New Delhi metallo-betalactamase-1 (NDM-1) producing Enterobacteriaceae. NDM-1 is an enzyme that makes bacteria resistant to a broad range of antibiotics. First detected in a Swedish patient of Indian origin in 2008, the gene for NDM-1 can spread from one strain of bacteria to another and has since been detected in the US, the UK, Canada and Japan besides India.
Sarkar said rGO was earlier not known to be harmful. But his study has shown for the first time that in the presence of air and visible light, it is able to readily generate ROS – chemically reactive molecules containing oxygen – that are toxic. "We decided to exploit such toxicity to combat some stubborn hospital pathogens."
The researchers prepared graphene oxide by standard method and reduced it by using four conventional reducing agents (like hydrazine hydrate, sodium borohydride, hypophosphor methodous acid and sodium dithionite) to get rGOs of different shades. Antibiotic resistant Enterobacter pathogens were chosen to find the effect of rGO on their growth in culture, Sarkar said. The experiment involved adding a tiny quantity of rGO to a bacterial culture of Enterobacter species and exposing the culture to 60 watt glowing tungsten bulb light for 2 hours at 37ºC.
Microscopic examination of smears taken at the end of the experiment showed reduced growth of the bacterial cells in the presence of rGO compared with the control culture that was not treated with rGO.
"This clearly suggests that microbial contamination can be readily avoided by using rGO to combat the growth of hospital pathogens," the report concludes.
It however cautions that one should use graphene oxide with the utmost care. Though it is nontoxic to start with, it gets slowly reduced even in the open environment on ageing with the formation of rGO that is toxic, says Sarkar.
"rGO is extensively used in the search for super capacitor and new molecules for trapping solar energy," he said. "For such work people handle this without knowing its toxic effect. Our study has been the first to show that rGO generates harmful ROS in air under visible light.
Sarkar said while his study exploited the toxicity of rGO to fight hospital pathogens, adequate precaution must be taken by those who use it for research.
1. Dutta, T et al. ROS generation by reduced graphene oxide (rGO) induced by visible light showing antibacterial activity: comparison with graphene oxide. RSC Adv. 5, 80192 (2015) doi: 10.1039/c5ra14061g