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Vol. 26, No 3, 4
Julio - Diciembre 2018
An International Refereed Scientic Journal
of the Facultad Experimental de Ciencias
at the Universidad del Zulia
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ISSN: 1315-2076
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 3, 4, Julio - Diciembre 2018
CIENCIA 26 (3,4), 74 - 78, 2018
Maracaibo, Venezuela
Eect of magnetic elds on the growth of bacterium
Staphylococcus aureus
Nomar Zambrano
1
, Gabriela Pérez M.
2
, Rodolfo Salas Auvert
3
, José R. Fermín
*4
1
Campus URBE, Prolongación Circunvalación No. 2 con Av. 16 Guajira, Maracaibo, Zulia, Venezuela
2
Facultad de Humanidades, Arte y Educación, Universidad José Gregorio Hernández, Maracaibo, Zulia,
Venezuela
3
Departamento de Biología, Facultad Experimental de Ciencias, Universidad del Zulia, Aptdo. Postal 526,
Maracaibo 4001, Zulia, Venezuela
4
Departamento de Física, Facultad Experimental de Ciencias, Universidad del Zulia, Aptdo. Postal 526,
Maracaibo 4001, Zulia, Venezuela
Facultad de Ingeniería. Universidad Rafael Urdaneta. Maracaibo 4005, Zulia, Venezuela
jfermin70@gmail.com
Recibido: 19-07-2018 Aceptado: 22-10-2018
Abstract
The eects of weak static and low-frequency magnetic elds on the growth rate of S. aureus were investigated.
The measurements were performed with static magnetic elds with magnitude in range 0.0 G ≤ Ho ≤ 14.0 G
and low-frequency magnetic elds at xed amplitude Ho
4.5 G, and frequency range 0.0 ≤ f ≤ 1.0 kHz. The
growth of these bacteria is negatively aected by increasing the intensity of the static magnetic eld. When
exposed to an oscillating eld, a positive eect was observed on the rate of growth of the colonies with respect
to the eld frequency. In both, static or ac magnetic eld, the growth curves follow an exponential law, typical
of asynchronous cell divisions.
Keywords
: Asynchronous growth; exponential growth; magnetic eld eect on microorganisms; S. aureus.
Efecto de campos magnéticos en el crecimiento de la bacteria
Staphylococus aureus
Resumen
Los efectos de campos magnéticos estáticos y de baja frecuencia sobre la tasa de crecimiento de S. aureus
fueron investigados. Las medidas fueron realizadas con campos magnéticos estáticos con magnitud en el rango
0.0 G ≤ H
o
≤ 14.0 G, y bajas frecuencias en el rango de 0.0 ≤ f ≤ 1.0 kHz, con amplitud de Ho
4.5 G. La tasa
de crecimiento de esta bacteria disminuye al incrementar la intensidad del campo estático. Sin embargo, en
presencia de un campo oscilante de baja frecuencia, se observa un efecto positivo en la tasa de crecimiento
respecto de la frecuencia del campo. En ambos campos, estático y variable, las curvas de crecimiento satisfacen
una ley exponencial, típica de una división celular asíncrona.
Palabras clave:
Crecimiento asíncrono; crecimiento exponencial; efecto de campos magnéticos en
microorganismos; S. aureus.
DOI: https://www.doi.org/10.5281/zenodo.5590918
75Zambrano et. al.,/ Ciencia Vol. 26, Número Especial (2018) 74-78
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 3, 4, Julio - Diciembre 2018
Introduction
Nowadays the exposure of living tissue to various
types of electric and magnetic elds is a commonly
encountered event: extremely low frequency from
power lines, high frequency electromagnetic elds
(EMF) from cellular phones, and computers.
Since this is a task of medical and technological
importance, a number of attempts have been given
to clarify the eects of electric and magnetic elds
on biological cells
1
.
S. aureus is a human pathogen responsible for a
variety of community-acquired diseases, belonging
to the class of gram-positive bacteria 2. With the
spread of this bacterium, the number of antibiotic
agents has increased and along with these, stronger
antibiotic resistance proles have been observed 3,
4. This requires new and more ecient methods
for treating infections. One of the techniques used
for medical purposes is the magnetic eld therapy
or magnetotherapy 5, which is often applied in the
treatment of many diseases such as bone fractures
6, pain syndromes 7, and cancer 8. Also, pulsed
magnetic eld-based methods are also employed as
non-thermal preservation techniques to minimize
the risk of microorganism contamination 9, 10.
This is because of the proven ability of oscillatory
elds to cause damage in living cells. However, the
eects are not fully understood, since some of the
results have been inconsistent 11. In other cases the
results often contradict each other, which include
an increase or decrease in the rate of cell division
in E. coli and S. aureus, when these strains are in
presence of a magnetic eld 12-14. Some other
studies found that magnetic elds could be a general
stress factor in bacteria 15. The general stress
response to a magnetic eld is found in all bacteria,
and living cells and is remarkably conserved across
specie. In a study on the mutagenicity of magnetic
elds exposure, Ikehata 16 also reported that strong
static magnetic elds can cause mutations in S.
typhimurium and E. coli.
In this work we study the eects of weak static
and low-frequency magnetic elds on the growth of
bacterium Staphylococcus aureus. From an analysis
of the growth curves, we have found that the main
eect of the magnetic eld on the growth dynamics
of S. aureus is to aect the time required for the cell
divisions.
Experimental
Fresh S. aureus strains were used throughout the
experiments. Nutritive Broth (Merck, Darmstadt)
and Plate Count Agar (Difco, Detroit) were used
for cultivation of the bacteria. Salt solution 0.75%
was used to make serial dilutions until 10
-5
ml. The
control cultures were kept in the same conditions as
the exposed ones except the sole exposition to the
magnetic elds. The number of colonies forming
units (CFU) of the bacterial cultures was measured
independently as a function of the magnetic eld
intensity (H
o
), and frequency (f).
The magnetic elds were generated by a
homemade 600 turned cylindrical coil (12 cm radius
and 30 cm length), and were measured by a Hall
eect probe Gaussmeter. Two dierent experiments
were performed: (a) the cells were exposed to static
magnetic elds with amplitude varying from 0.0 to
14.0 G and (b) with the cells exposed to oscillating
magnetic elds with frequencies ranging from 0.0
Hz 1.0 KHz and xed intensity of the order of 4.5
G. The magnetic elds inside the solenoid were
approximately homogenous in a region ± 3 cm o
the center of the coil. The device was kept at 37°C
in an incubator cabinet and it was measured by a
thermometer.
The samples were placed rst into glass tubes on
a nonconductive stand (homemade) along the axis
of the coil, and then introduced inside the solenoid
during exposure times from 0 h to 6 h. In order to
reduce the uncertainty in our measurements and
to obtain reliable results, each test was performed
independently up to 4 times keeping the same
experimental conditions.
Results and discussion
1. Eect of static magnetic elds
The main eect of the static magnetic eld on
the growth dynamics of the bacterium S. aureus is
shown in Fig. 1. Each symbol is an average from 4
independent measurements performed previously.
We found that the number of CFU increases with the
time of exposure and decreases with the magnitude
of the applied eld.
76 Eect of magnetic elds on the growth of bacterium Staphylococcus aureus
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 3, 4, Julio - Diciembre 2018
Fig. 1. Dependence of the colony forming units
(CFU) on the time of exposure for several magnetic
eld intensities. The solid curves are ts to the
exponential function e
t/τ
, as described in the text.
The curve for H
o
=0.0 G ( ) correspond to the control
culture.
These results are in agreement with previous
studies which also found the magnetic eld intensity
negatively aects the growth of S. aureus
12
. It is also
observed that the cells remain in lag state up to
certain time of exposure, after which, cell division
is activated growing in an exponential trend. To
estimate the quantity τ, we assume that the growth
dynamics is governed by some mechanism following
the exponential law et/τ, where t is the exposure
time and τ is related to the time required for a cell
division, and is an intrinsic parameter to the species
in its environment. These functions are commonly
used to describe asynchronous growth in population
dynamics 17. In an asynchronous process, the
division might occur at dierent times in each cell.
The solid curves in Fig. 1 represent exponential
functions with τ =0.48, 0.50, 0.53, 0.61, and 0.62
hours, for H
o
= 0.0, 6.0, 8.0, 12.0 and 14.0 G,
respectively. These results are plotted in Fig. 2, and
show that as the magnetic eld intensity is increased
the growth process is decelerated, but not stopped.
The dashed line is a guide to the eyes.
Fig. 2. Activation time, τ, as a function of the
magnetic eld strength. The dashed line is to guide
to eyes.
Although the dc magnetic eld decreases the
number of colony forming units, is it not obvious
that the cells loose their ability to divide. This means
that the inhibitive eect of the static eld is not fully
bacteriostatic in this range of magnetic elds. Since
the growth curve of the control culture (H
o
= 0.0 G)
is also exponential, we conclude that the asynchrony
in the cell division is inherent of the preparation
conditions, and independent of external agents such
as a dc magnetic eld.
2. Eect of low frequency magnetic elds
When exposed to an oscillatory magnetic eld,
bacteria can behave unexpectedly. To study this
behavior, treads of S. aureus were grown in-situ in
presence of a magnetic eld with frequency ranging
from 0.0 Hz to 1.0 kHz. After an exposure time of
about 6.0 h, we counted the number of CFU of the
exposed cultures and compared with the control
(f=0.0 Hz). The resulting growth curves of S.
aureus are shown in Fig. 3 for several frequencies.
As in the case of the dc magnetic eld the CFU
increase exponentially with exposure time, but on
the contrary, it increases rapidly with increasing
frequency. These curves are adjusted to exponential
functions of the type e
t/τ
(solid lines), with τ values
depending monotonically on the frequency of
the magnetic eld, as shown in Fig. 4. The dotted
line is a guide for the eye. This fact can be used to
understand the dynamics of the bacterial growth.
77Zambrano et. al.,/ Ciencia Vol. 26, Número Especial (2018) 74-78
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 3, 4, Julio - Diciembre 2018
Fig. 3. Dependence of the colony forming units (CFU)
on the time of exposure for several frequencies.
Solid lines are ts to the exponential function e
t/τ
,
as described in the text. The curve for f = 0.0 Hz ( ),
correspond to the control culture.
Fig. 4. Activation time, τ, as function of the frequency
of the ac magnetic eld. The dotted line is a guide for
the eye.
According to these results, the growth dynamics
in S. aureus cultures is governed by a synchronous
frequency-independent mechanism, and the eect
of frequency is to accelerate the cell division process.
Our results indicate that the weak static eld of a
few G after a few hours give a measurable change in
the growth rates of all of the bacterial species and
are in agreements with previous works18,19.
Conclusions
We have presented and discuss and experimental
investigation on the eect of dc and ac magnetic
elds on bacterium S. aureus. It was found that as
prepared, the growth dynamics is governed by a
synchronous mechanism. Although this mechanism
is qualitatively unaected by the magnetic eld,
the rate of growth decreases for increasing the eld
intensity, and increases for increasing the eld
frequency. We have determined that the activation
time for the cell division depends on both magnitude
and frequency of the applied eld.
The question of how the growth dynamics of
bacteria is aect by a magnetic eld is not completely
answered, and still an open issue. The fact that the
activation time for a cell division can be expressed
as a function of the magnitude and frequency of
the magnetic eld, can be important to understand
metabolic changes due to ion transport across the
cell membrane.
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Esta revista fue editada en formato digital y publicada
en diciembre de 2018, por el Fondo Editorial Serbiluz,
Universidad del Zulia. Maracaibo-Venezuela
Vol.26 Nº3, 4
