Combined application of sub-toxic level of silver nanoparticles with low powers of 2450 MHz microwave radiation lead to kill Escherichia coli in a short time

Objective(s): Electromagnetic radiations which have lethal effects on the living cells are currently also considered as a disinfective physical agent. Materials and Methods: In this investigation, silver nanoparticles were applied to enhance the lethal action of low powers (100 and 180 W) of 2450 MHZ electromagnetic radiation especially against Escherichia coli ATCC 8739. Silver nanoparticles were biologically prepared and used for next experiments. Sterile normal saline solution was prepared and supplemented by silver nanoparticles to reach the sub-inhibitory concentration (6.25 μg/mL). Such diluted silver colloid as well as free-silver nanoparticles solution was inoculated along with test microorganisms, particularly E. coli. These suspensions were separately treated by 2450 MHz electromagnetic radiation for different time intervals in a microwave oven operated at low powers (100 W and 180 W). The viable counts of bacteria before and after each radiation time were determined by colony-forming unit (CFU) method. Results: Results showed that the addition of silver nanoparticles significantly decreased the required radiation time to kill vegetative forms of microorganisms. However, these nanoparticles had no combined effect with low power electromagnetic radiation when used against Bacillus subtilis spores. Conclusion: The cumulative effect of silver nanoparticles and low powers electromagnetic radiation may be useful in medical centers to reduce contamination in polluted derange and liquid wastes materials and some devices.