Electromagnetic irradiation of Enterococcus hirae at low-intensity 51.8- and 53.0-GHz frequencies: Changes in bacterial cell membrane properties and enhanced antibiotics effects

Abstract

Exposure to electromagnetic irradiation (EMI) of 51.8 and 53.0 GHz and low intensity (flux capacity of 0.06 mW cm-2) for 1 h markedly decreased the energy-dependent H+ and K+ transport across membranes of Enterococcus hirae ATCC 9790. After EMI, there was also a significant decrease of overall and N,N'-dicyclohexylcarbodiimide (DCCD)-sensitive ATPase activity of the membrane vesicles. These measures were considerably lower at 53.0 GHz. EMI in combination with different antibiotics, such as ceftriaxone and kanamycin at their minimal inhibitory concentrations (100 and 200 μM, respectively), enhanced bacterial cell growth and altered their membrane transport properties. Total H+ efflux was most sensitive to ceftriaxone but DCCD-inhibited H+ efflux and total K+ influx were sensitive to kanamycin. The results indicate that cell membrane proteins could be a target in the action of EMI and enhanced antibacterial effects in combination with antibiotics. The DCCD-sensitive F0F1-ATPase or this ATPase in combination with K+ uptake protein probably plays a key role in these effects. © 2012 Federation of European Microbiological Societies.