Silver nanoparticles have been shown to have antimicrobial effects and remarkable disinfection efficacy against a range of water microorganisms. In the present work, Klebsiella pneumoniae was used as a water treatment model, as it survives in a wide range of water environments. Silver nanoparticles of higher stability and different sizes were synthesized by the arc discharge method. The combination of 30 min exposure to 0·32 mT, 20 Hz pulsed magnetic field and treatment with silver nanoparticles with serial concentrations (10:500 parts per million) and different sizes (94, 38 and 17 nm) was used to study the antibacterial effects against K. pneumoniae. Confirmation of silver nanoparticles by using an ultraviolet–visible spectrometer, a particle size analyzer and a high-resolution transmission electron microscope depicted three sizes (∼94, ∼38 and ∼17 nm) at rotational speeds (0, 350 and 950 revolutions/min, respectively). The antibacterial results indicated serially more inhibition of bacterial growth with increase in silver nanoparticle concentration, with the maximum effect of more than 70% inhibition produced by 17 nm silver nanoparticles. Particularly, the combination of pulsed magnetic field and silver nanoparticles (17 nm) indicated significant enhancement in growth inhibition by 56·7% compared to each alone. The study presents a new trend for water disinfection with significant impact of such combination effects on K. pneumoniae with low silver nanoparticle concentrations and less toxicity.

The arc discharge technique with some modifications was carried out to synthesize a high percentage of metallic zinc (Zn) nanoparticles (ZnNPs) with a high degree of structural perfection. The antibacterial potentials of the synthesized ZnNPs against common waterborne bacterial pathogens were compared as a more applicable disinfection method than conventional ones. The obtained characteristics (X-ray diffraction, energy-dispersive X-ray spectroscopy and transmission electron microscopy) of the prepared ZnNPs indicated their perfect hexagonal surface shape and the high purity of the zinc metal. Moreover, the prepared nanoparticles showed significant bacteriostatic and bactericidal effect against the various tested bacteria. The findings of this study support the use of ZnNPs as a strong antibacterial agent in water desalination plants and manufacturing of water filters. Moreover, the findings suggest the use of the arc discharge technique for preparing more effective nanometals with different shapes and high purity.

The over-reliance on antibiotics and their enormous misuse has led to warnings of a future without effective medicines and so, the need for alternatives to antibiotics has become a must. Non-traditional antibacterial treatment was performed by using an aray of nanocomposites synergised with exposure to electromagnetic waves. In this manuscript, electrospun poly(vinyl alcohol) (PVA) nanofiber mats embedded with silver nanoparticles (Ag NPs) were synthesized. The nanocomposites were characterized by Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Current-Voltage (I-V) curves, and Thermogravimetric analysis (TGA) along with analysis of antibacterial impact against E. coli and S. aureus bacteria, studied by bacterial growing analysis, growth kinetics, and cellular cytotoxicity. The results indicated a spherical grain shape of silver of average size 20 nm and nanofibers’ mean diameter of less than 100 nm. The nanocomposite mats showed good exposure to bacteria and the ability to sustain release of silver for a relatively long time. Moreover, the applied electromagnetic waves (EMWs) were shown to be a synergistic co-factor in killing bacteria even at low concentrations of Ag NPs. This caused pronounced alterations of the bacterial preserved packing of the cell membrane. Thereby, the treatment with nanocomposite mats under EM wave exposure elucidated maximum inhibition for both bacterial strains. It was concluded that the functioning of nanofiber with silver nanoparticles and exposure to electromagnetic waves improved the antibacterial impact compared to each one alone.

The widespread use of antibiotics in diverse areas led many bacterial strains to become highly resistant. Thus, considerable concerns were recently raised to overcome and/or to find other alternatives to the use of antibiotics. In this context, combining antibacterial effects of exposure to pulsed magnetic signals and supplying of silver nanoparticles recently indicated a significant bactericidal impact. The interplay between silver nanoshapes (spheres, rods and prisms) and exposure to pulsed magnetic signals (0·32 mT, 20 Hz–30 min) was studied to explore whether engineering of silver nanoshapes has a synergistic antibacterial effect against Klebsiella pneumoniae. In this regard, the bacterial growth rates, kinetics and enzymatic changes (protein leakage and lactate dehydrogenase levels) were investigated. The results confirmed that silver nanoprisms with a higher specific-area-to-volume ratio and appreciable analogy of charge distribution exhibit the highest synergistic inhibition effect with pulsed magnetic signals by 35% at 10 parts per million concentration. Moreover, the coupling of magnetic signals with nanoprisms showed significant cellular injuries and loss of membrane integrity as a consequence of the elevation of lactate dehydrogenase and protein leakage levels by more than fivefold and 15-fold, respectively. These new findings substantiate the antibacterial synergism of silver nanoparticles with pulsed magnetic signals in a shape-dependent manner.

The effect of exposure to 0·1 Hz–0·1 kHz pulsed magnetic fields on models of gram-positive and gram-negative bacterial cells was investigated. The possible alterations in the electrical characteristics of dead and alive bacteria cells were monitored by using dielectric spectroscopy. The dielectric dispersions of cells were obtained over the range 42 Hz–8 MHz by measuring their dielectric permittivity and conductivity. The acquired results indicated exposure enhancement and inhibition effects on both bacterial models in different frequency windows. The spectroscopy results for all bacterial cells indicated two sizeable dispersions in low- and high-frequency ranges (so-called α- and β-dispersions) due to different polarization mechanisms. Remarkable variations in the dielectric relaxations were observed due to exposure as a result of possible alterations in the counterion clouds and ionic membrane permeability, plasma and cell wall charge residues. In conclusion, both bacterial models demonstrated considerable response to exposure, resulting in a significant electrochange in the cell membrane/wall structure. Moreover, by performing dielectric spectroscopy, it is possible to distinguish between normal and abnormal cells. It is worth mentioning that the observed results can be achieved when using resonance frequencies outside the range used in the study.

The effect of square pulsed magnetic signals on the growth of Dickeya solani bacterium was studied. Three different frequency windows in a range up to 50 Hz were selected for exposure to determine the frequencies causing maximum bacteriostatic and bactericidal effects. Furthermore, the cellular morphological changes under most inhibitory conditions were studied and bacterial pathogenicity was examined. The obtained data showed the most inhibitory frequency that caused an inhibition by 65% and delayed the cellular growth by more than 8 h is 5 Hz. The morphological studies of exposed bacterium cells showed cellular abnormalities and fragmentations and loss of membrane outer surface charges. The pathogenicity test exposed a significant decrease in the infection reached 68%. In conclusion, the present study developed better disease strategy for controlling the bacterium of D. solani in an efficient and safe manner. Moreover, the applicability of using pulsed electromagnetic signals may have a good role in bacterial inhibition.