Effect of Frequency Magnetic field on Gram Positive and Gram Negative Bacteria CURRENT STATUS: UNDER

Objective It is necessary to evaluate the harmful or useful effects of electromagnetic waves on living organisms and determine the threshold of these radiations. In this research, the effect of magnetic fields on the growth of gram-positive ( Staphylococcus aureus ) and gram-negative ( Escherichia coli ) bacteria has been evaluated. Results In Gram-negative bacteria such as E. coli in both magnetic fields 1mT and 2mT at different frequencies, an additive effect was seen on the growth of bacteria. When the frequency increased the trend of increasing bacterial growth, slowed. In Gram-positive bacteria such as Staphylococcus, this effect was less. In 1mT magnetic field, the growth of bacteria was seen but the 2mT field was virtually ineffective and the differences between two groups at different frequencies were not significant. Also, significant changes didn't observe with increasing frequency. Study of bacterial growth in terms of frequency in both case and control groups showed an increasing trend. With increasing frequency from 50 Hz to 150Hz significantly increased the rate of bacterial growth and the growth in the higher frequencies more than lower frequencies. Magnetic field had increment effect on the growth of bacteria. This effect was greater on gram-negative than on gram-positive.


Introduction
Today's use of electrical devices has a wide role in human life. Electromagnetic fields, similar to those found in overhead power lines and other electrical devices can have a biological effect. The effects of electromagnetic fields on living organisms have been a subject of active investigation these years. In the past two decades' people have concerns about the potential harm of exposure to Low-Frequency Magnetic Fields (ELF-EMF) with frequencies below 300 Hz that is common in the human environment.
Some studies have been established to verify the effects of ELF-EMF on cell functions (1,2). The effect of ELF-EMF has also been evaluated on bacteria in the studies (3)(4)(5). The results have been showed that ELF-EMF can negatively (6,7) or positively (8,9) effect on the living systems functions and bacteria antibiotic sensitivity, so some results are in contrast with each other. The previous studies have shown that the effects of ELF-EMF are depending on some parameters such as frequency and intensity of the field, time of exposure and type of bacteria cells. But due to the complexity of biological systems, there is not the final agreement on the effect of ELF on bacteria as a living system (10). So it seems that more investigation about this subject is necessary. In this work, the effect of ELF-EMF exposure on bacteria growth by changing these parameters: frequency (50, 75, 100 and 150 Hz), magnetic field (1 and 2 mT) and type of bacteria (gram positive and gram negative) have been investigated.

Methods
Electromagnetic generation system: Electromagnetic exposures were produced by our homemade electromagnetic generator (previous study) developed and set up in the department of medical physics of Arak University of Medical Sciences. The basic part of this system is consisting of a pair of Helmholtz coils by using power supply and signal generator (Fig 1).
This system has selection button that user can select desired frequency between 0 (as a static magnetic field) to 300 Hz (as a pulsating magnetic field) and it can produce magnetic fields with intensities from 0 to 8 mT. The efficiency and precision of the apparatus were checked by a gaussmeter. The uniformity of the electromagnetic field between the coils allowed simultaneous exposure to the cultures. This feature was in good agreement with the computation of the field distribution and homogeneity calculated by a Laplace equation simulation program, which takes into consideration the finite dimensions of coils. In this study, magnetic fields with frequencies (50, 75, 100 and 150 Hz) and intensities of (1 and 2 mT) were used on two types of bacteria (gram positive and gram negative).

Results
The magnetic fields effect on the bacterium growth showed by colony forming unit on the Muller Nawrotek and his colleagues. They reported that E. coli and S. aureus showed increased cell proliferation and survival in the pretreatment with magnetic waves. Therefore, the presence of these bacteria in the vicinity of the magnetic field can make it difficult to treat the diseases caused by these pathogens.

Limitations
The Electrical devices have a major role in this study were produced by our homemade electromagnetic generator this step is the major limitation in designed of the study.