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Microwaves are non-ionizing electromagnetic waves with frequencies between 0.3 and 300 GHz. Both humans and microorganisms living on the human body are exposed to significant doses of microwave radiation in everyday life. Whether and how microwave radiation could influence the viability and growth of microorganisms is the subject of this educational paper. Studies on the effects of microwaves on the growth of microbial cultures were searched for in biomedical journals indexed in MEDLINE from 1966 to 2012. The published studies showed that microwaves produce significant effects on the growth of microbial cultures, which vary from the killing of microorganisms to enhancement of their growth. The nature and extent of the effect depend on the frequency of microwaves and the total energy absorbed by the microorganisms. Low energy, low frequency microwaves enhance the growth of microorganisms, whereas high energy, high frequency microwaves destroy the microorganisms. However, neither the effects of a wide spectrum of frequencies nor the effects of a wide range of absorbed energies have been investigated. Considering the potentially deleterious influence of microwaves on the symbiotic balance between microorganisms and the human host, further research on the effects of the complete frequency and energy spectra of microwave radiation on the growth of microorganisms is necessary.
ISSN 2334-9492 (Online)
© The Serbian Medical Society 2014
UDC: 579.8:537-962
Education article
Hospital Pharmacology. 2014; 1(2):102-108
Corresponding author:
Prof. Slobodan M. JANKOVIĆ, MD, PhD, Prim.
Specialist in general surgery; subspecialist in clinical pharmacology
Faculty of Medical Sciences, University of Kragujevac, Svetozara Markovića 69, 34000 Kragujevac, Serbia
The Effects of Microwave Radiation on
Microbial Cultures
Slobodan M. Janković, Milorad Z. Milošev, Milan LJ. Novaković
Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia
Microwaves are non-ionizing electromagnetic waves with frequencies between . and 
GHz. Both humans and microorganisms living on the human body are exposed to significant
doses of microwave radiation in everyday life. Whether and how microwave radiation could
influence the viability and growth of microorganisms is the subject of this educational paper.
Studies on the effects of microwaves on the growth of microbial cultures were searched for in
biomedical journals indexed in MEDLINE from  to . The published studies showed
that microwaves produce significant effects on the growth of microbial cultures, which vary
from the killing of microorganisms to enhancement of their growth. The nature and extent
of the effect depend on the frequency of microwaves and the total energy absorbed by the
microorganisms. Low energy, low frequency microwaves enhance the growth of microor-
ganisms, whereas high energy, high frequency microwaves destroy the microorganisms.
However, neither the effects of a wide spectrum of frequencies nor the effects of a wide range
of absorbed energies have been investigated.
Considering the potentially deleterious influence of microwaves on the symbiotic balance
between microorganisms and the human host, further research on the effects of the complete
frequency and energy spectra of microwave radiation on the growth of microorganisms is
Keywords: microwaves; microbial cultures; frequency; absorbed energy; growth
Interactions between various types of electro-
magnetic radiation and living organisms have
attracted the attention of scientists since the
introduction of technical devices that operate
using electromagnetic waves. In the last decade,
the human population has been increasingly
exposed to radiation from microwave-operat-
ing devices, such as radars, diathermy devices,
and cellular or cordless phones; in the first quar-
ter of 2012 the number of mobile phone users
in China increased to 1 billion [1]. Together
with humans, thousands of bacterial species
and yeasts living on or in the human body are
exposed to significant doses of microwave radi
ation. Whether and how microwave radiation
could influence the viability (ability of micro-
organisms to survive in hostile environment),
pathogenicity (ability of microorganisms to
cause a disease) and growth of microorganisms
is the subject of this review.
Microwaves are non-ionizing electromagnetic
waves with frequencies between 0.3 and 300
GHz (i.e., with wavelengths from 1 meter to 1
millimetre, respectively) [2]. The most import-
ant sources of microwave radiation that humans
may encounter are various industrial microwave
Janković SM et al: The Effects of Microwave Radiation on Microbial Culture
generators used for communications, that speed
up chemical reactions or are used for heating
(896 or 915 MHz); cellular phones (824–850,
900, 1800 or 1900 MHz); cordless phones (from
46 to 5800 MHz); microwave ovens (915 and
2450 MHz); certain diathermy applicators (915
and 2450 MHz); UHF radios (from 470 to 890
MHz); dish antennas (from 0.8 to 15 GHz); and
traffic radar (10.5 and 24 GHz). The energy of
microwaves is relatively low: one quantum has
approximately 10
electron volts (eV), which
is considerably lower than the quantum energy
needed for the ejection of an electron from a
molecule or the breaking of an intra-molecu-
lar bond (> 10 eV) [3]; therefore, microwave
radiation is considered non-ionizing radiation.
When irradiating living organisms, micro-
waves produce two types of effects: thermal
and non-thermal. Thermal effects are the con-
sequence of absorption of microwave energy
by cell molecules, causing them vibrate much
faster and producing general heating of the
cell [3]. The extent of microwave absorption
within a cell depends on its dielectric constant
and electrical conductivity [3]. The concept of
non-thermal effects of microwaves came from
experiments in which bacterial cultures were to
a large extent destroyed by microwave-induced
heating than by other heating methods produc-
ing the same working temperature and from
studies showing an increase in the growth of
bacteria induced by microwaves [4]. The mech-
anism of the non-thermal action of microwaves
is still not completely understood. However, it
seems that changes in the secondary and/or
tertiary structure of functional proteins ensue
as a consequence of rotation and lining-up of
the molecules with a rapidly alternating electric
field (more than a billion times per second) [4].
Billions of bacterial cells and yeasts live on the
human skin and mucosal surfaces, engaging in
a symbiotic relationship with the host. Recently,
it was estimated that 500 to 1,000 species of bac-
teria live in the human gut. Symbiotic bacteria
are useful to humans in a variety of ways: they
promote digestion of food and absorption of
nutrients, they synthesise vitamins (vitamin K
and biotin), they prevent the colonization of
pathogenic bacteria, and they improve func-
tioning of the immune system [5]. Symbiotic
bacteria on human skin even stimulate the pro-
duction of antimicrobial peptides by the cells of
the skin epithelium, aiding the skins defense
against pathogenic bacteria [6]. However, the
disruption of this symbiosis by external factors,
which either massively destroy commensals
(e.g., by antiseptics or antibiotics) or excessively
increase their growth (e.g., blind intestinal loop
syndrome or excretion of dextrose in urine),
may have adverse consequences on human
health and decrease defence against pathogenic
microbes [7]. In this way, many serious bac-
terial infections may ensue, like gastroenteri-
tis, pneumonia, urinary tract infections, skin
infections, etc. Considering the overwhelming
presence of microwave radiation in the human
environment, interactions between microwaves
and microorganisms have great potential to sig-
nificantly influence human health.
Overall effects on growth
How microwaves will affect the growth of
microorganisms depends primarily on the fre-
quency of the radiation and the total energy
absorbed by the microorganisms (absorbed
dose). When microwaves are applied at certain
frequencies, with high energy and for a suffi-
ciently long period of time, their thermal effect
is most likely dominant and kills bacterial cells
or yeasts. Numerous experiments with micro-
wave irradiation of various cultures of bacteria
and yeasts in a wet environment such as a water
suspension did not show additional killing of
the microbes by microwaves compared to that
caused by conventional heating to the same
temperature [8, 9, 10]. However, in a dry envi-
ronment, the killing effect of microwave radia-
tion was significantly decreased and happened
only after a prolonged period of irradiation,
most likely due to a lower transformation of
microwave energy to heat. Some of the stud-
ies even showed that the extent of killing of
microorganisms (bacteria and bacteriophages
[viruses that attack bacteria]) was correlated
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Hospital Pharmacology. ; ():-
with the moisture content of the experimental
In contrast, when microorganisms were
irradiated with microwaves at temperatures
lower than the thermal destruction level; var-
ious effects were observed, from killing to
enhanced growth. A specific killing effect of
microwaves on Escherichia coli, different from
the effect of hyperthermia, was observed in sev-
eral studies [11].
Thermal effects on growth
Because it was observed that the heating of
microorganisms to a certain temperature by
microwaves could kill them, many studies were
performed attempting to establish the minimal
dose of microwave energy that could be used
for disinfection or sterilization purposes. In
a study on toothbrushes contaminated with
Streptococcus mutans, a type of bacteria that
can cause dental caries, radiation from a micro-
wave oven at “high power” for five minutes
completely decontaminated the toothbrushes;
it was more effective than the antiseptic
cetylpyridinium chloride or UV-radiation [12].
Another study showed that microwaves could
be effectively used for reducing the number
of bacteria on previously worn dentures [13].
Microwaves with frequencies of 18 GHz, used
on bacteria that contaminated bovine pericar-
dium prepared for the construction of artifi
cial heart valves, showed a strong inactivating
effect. Cultures of Staphylococcus aureus and
Escherichia coli were completely inactivated
after three consecutive exposures to radiation
with such characteristics [14]. When cultures
of Escherichia coli and spores of Bacillus cereus
were exposed to the maximum microwave
power in a home microwave oven, they were
completely destroyed after two and four min-
utes, respectively [15].
The thermal killing effect of microwaves
is non-selective, and various species of micro-
organisms will also be destroyed if a suffi-
cient dose is used (Table 1). When cultures
of Pseudomonas aeruginosa, Staphylococcus
aureus, Candida albicans, and Bacillus subtilis
contaminating dental resin were irradiated with
microwaves in a wet environment at 650 W for
1, 2, 3, 4 or 5 minutes, the killing effect was
observed after an exposure of two minutes or
longer. Candida albicans was more susceptible
to microwave radiation than bacterial cultures
[16]. Similar effects were obtained for micro-
waves irradiating the same species of bacteria
inoculated on dentures in a wet environment at
650 W for 6 minutes. S. aureus and C. albicans
inoculums were completely destroyed, while
the number of P. aeruginosa and B. subtilis
cells was greatly reduced [17]. Being non-se-
lective, the killing effect of microwaves is syn-
ergistic with the effects of other non-selective
killing agents, such as disinfectants. In a study
of the interaction between microwaves and
the disinfectant hydrogen peroxide (0.08%),
the synergistic killing effect was achieved on
Escherichia coli and Pseudomonas aeruginosa
cultures after exposure for 10 minutes and a
maximum obtained temperature of 60°C [11].
Some environmental conditions may dimin-
ish the deleterious thermal effect of micro-
waves on microbes, including an increase in
the concentration of sodium chloride within
the extracellular medium. When cultures of
Staphylococcus aureus, Salmonella enteritidis,
Escherichia coli and Bacillus cereus inoculated
in a mashed potato preparation were exposed to
microwave (2450 MHz) heating for 1 min at 800
W, the percentage of killed cells was inversely
proportional to the concentration of sodium
chloride in the medium [18].
Non-thermal effects on growth
2An interesting finding was made in the study
of Grundler et al. [22]: at frequencies of 41, 640-
41, and 835 MHz, microwaves showed a reso-
nant-like effect on the growth of some yeasts,
including Saccharomyces cerevisiae, which
was not dependent on the amount of absorbed
energy from the microwaves. The growth was
interchangeably enhanced or decreased at steps
of 10 MHz within the frequency range stud-
ied. The mechanism of this effect could not be
explained by the authors.
Possible mechanisms of non-thermal
effects of microwaves on microbial
Understanding the mechanism of non-ther-
mal action of microwaves on microorganisms
is very important for the possible future use
of microwave technology or for avoidance of
its deleterious effects on humans, who live in
symbiosis with microbes. Not much is known
Janković SM et al: The Effects of Microwave Radiation on Microbial Culture
about the mechanisms because previous studies
have been limited in number and scope [23].
In a study in which Escherichia coli cultures
were exposed to microwaves (18 GHz, absorbed
power 1500 kW/m2, electric field 300 V/m) at
temperatures below 40°C (to avoid the ther-
mal effects of microwaves), transient mor-
phological changes (dehydrated appearance)
and openings of pores in the cell membrane
(approximately 20 nm in diameter, enabling
passage of dextran molecules) were observed
[24]. It seems that this effect is electro kinetic
in nature (caused by increased movements of
anions and cations), causing localized struc-
tural disarrangements of the cell membrane,
which results in the emergence of pores. Large
membrane pores cause leakage of vital intracel-
lular molecules out of the bacterial cells, which
may lead to their death. The effect was revers-
ible because more than 87% of exposed cells
remained viable. Similar effects of microwaves
on cell membranes were observed in another
study [25] in which Bacillus licheniformis
spores were irradiated with microwaves (2450
MHz, 2 minutes, 2 kW), which caused spore
cortex hydrolysis (brake of molecular bonds by
insertion of water), swelling and finally rupture,
as well as rupture of the inner membrane. This
effect could be attributed to the non-thermal
action of microwaves because the same tem-
perature (as produced by the microwaves) did
not cause such changes in the spore coat and
inner membrane. When microwave radiation of
the same characteristics was applied to Bacillus
subtilis vegetative forms [26], cell walls were
disrupted, and the aggregation of cytoplasmic
Table 1. Effects of microwaves on microbial cultures depending on the frequency, power (or delivered energy) and microbial species
Frequency of microwaves
800–1900 MHz 2450 MHz 18 GHz 41.640-41.835 GHz 99 GHz
Not reported
1–2 W; 30, 60,
120 and 180
E. coli, Klebsiella
550 W, 5–30
P. aeruginosa, P. acidovorans, S.
aureus and S. epidermidis,
S. aureus, E. coli,
600 W,
2–4 minutes
E. coli and spores of Bacillus
cereus, KILLED
650 W,
2–5 minutes
P. aeruginosa, S. aureus, Candida
albicans, and B. subtilis, KILLED
800 W, 1 minute S. aureus, Salmonella enteritidis, E.
coli and B. cereus, KILLED
10 and 60
5–60 minutes
Aspergillus versicolor and
Penicillium brevicompactum) and
actinomycetal (Thermoactinomyces
vulgaris and Streptomyces albus)
1500 kW/m2
E. coli,
PORES in the
cell membrane
2000 W,
2 minutes
Bacillus licheniformis spores,
19 hours
E. coli,
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(intracellular) proteins was detected on trans-
mission electron microscopy. Both the aggre-
gation of cytoplasmic proteins and swelling of
the cell wall were observed in Escherichia coli
and Bacillus subtilis after microwave irradiation
(2450 MHz and 600 W at 40, 60 and 80 degrees
of Celsius); these effects could not be attributed
to thermal damage because the same tempera-
tures from other heat sources did not produce
similar changes [27]. The disintegrating effect
of microwave irradiation is time-dependent,
where the intensity of the cell wall damage is
proportional to the total absorbed microwave
energy. Increases in irradiation time from 0 to
9 minutes resulted in a gradual increase in the
extracellular soluble chemical oxygen demand,
from 0.14 to 2.38 g/L (i.e., 72-fold).
Apart from their effects on cell membranes,
microwaves cause non-thermal acceleration
of enzymatic reactions in microbial cells, such
as non-aqueous esterification (formation of
ester-type of chemical compounds without
participation of water), and this effect is sub-
strate concentration-dependent [28]. Moreover,
microwaves can accelerate synthesis of glyco-
peptides in vitro (out of the living cells), which
may occur in microbial cells, changing their
functions [29]. It was shown in human cells that
microwaves could decrease the expression and
activity of certain functional proteins that cause
apoptosis. When SH-SY5Y cells, obtained by
retinoic acid-induced differentiation of human
neuroblastoma cells, were exposed for 2 h and 4
h to microwaves at a 1800 MHz frequency, mark
ers of apoptosis (heat-shock proteins 20, 27 and
70, caspase-3) were not increased. Instead, the
expression of Hsp 20 was decreased, potentially
prolonging survival of the tested cells [30]. Such
effect led to prolonged survival and increased
growth of neuroblastoma cells, originating
from an extremely malignant cancer. Similar
stimulatory effects of microwaves on growth
of Escherichia coli cultures were noted, but the
exact molecular mechanism of the effect was
not discovered. The irradiation of suspensions
of Escherichia coli by microwaves at a frequency
of 99 GHz for 19 hours caused a slight increase
in proliferation of the bacteria compared with
control suspensions. The mechanism of this
effect was not clear because the irradiation did
not influence approximately 90 different bio-
chemical reactions within the Escherichia coli
cell that were tested in the same study [31, 32].
Many studies show that microwave radiation
can have significant effects on the growth of
microbial cultures, which can vary from kill-
ing of microorganisms to enhancement of their
growth. The nature and extent of the effects
depend on the microwave frequency and the
total energy absorbed by the microorganisms.
It seems that low energy, low frequency micro-
waves enhance the growth of microorganisms,
while high energy, high frequency microwaves
destroy the microorganisms. However, neither
the effects of a wide spectrum of frequencies
nor the effects of a wide range of absorbed ener-
gies were investigated. Considering the poten-
tially deleterious influence of microwaves on
the symbiotic balance between microorganisms
and the human host, there is a high demand for
further research on the effects of the complete
frequency and energy spectra of microwave
radiation on the growth of microorganisms.
This review was partially financed by Grant No
175007 from the Serbian Ministry of Education
and by a Grant awarded by the Ministry of
Science of Montenegro.
Conflict of Interest Statement
The authors certify that there are no potential
conflicts of interest.
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Volume 1 Number 2 May 2014 HOPH
Hospital Pharmacology. ; ():-
Received: November 6, 2013
Accepted: December 21, 2013
Dejstva mikrotalasnog zračenja na kulture
Slobodan M. Janković, Milorad Z. Milošev, Milan LJ. Novaković
Fakultet medicinskih nauka, Univerzitet u Kragujevcu, Kragujevac, Srbija
Mikrotalasi su nejonizujući elektromagnetni talasi sa frekvencijama između 0,3 i 300 GHz. I ljudi
i mikroorganizmi koji žive na organizmu čoveka su izloženi značajnim dozama mikrotalasnog
zračenja u svakodnevnom životu. Predmet ovog edukativnog rada je pitanje da li i na koji način
mikrotalasno zračenje može da utiče na vitalnost i rast mikroorganizama.
Studije o efektima mikrotalasa na rast kultura mikroorganizama su tražene u biomedicinskim
časopisima indeksiranim u bazi podataka MEDLINE od 1966. do 2012. godine. Objavljene studije
su pokazale da mikrotalasi deluju na kulture mikroorganizama, bilo da ih ubijaju ili pospešuju
njihov rast. Priroda i veličina dejstva zavise od frekvencije mikrotalasa i ukupne energije koju
mikroorganizmi apsorbuju. Mikrotalasi male energije i niske frekvencije pospešuju rast mikro-
organizama, dok mikrotalasi velike energije i visoke frekvencije uništavaju mikroorganizme.
Međutim, dosad nisu ispitivana dejstva mikrotalasa šireg spektra frekvencija i većeg opsega
Uzimajući u obzir moguće štetne efekte mikrotalasa na simbiotičku ravnotežu mikroorganizama
i čoveka kao domaćina, neophodno je obaviti dodatna istraživanja delovanja čitavog spektra
frekvencija i energija mikrotalasa na rast mikroorganizama.
Ključne reči: mikrotalasi; kulture mikroorganizama; učestalost; apsorbovana energija; rast
... However, when microwave treatment is applied in winemaking, its possible effect on the microbial population and fermentation must be considered. Microbial cells can be affected by microwaves, depending on the frequency and intensity of radiation; some authors have observed cell destruction while others have proposed a microbial growth [33,34]. Carew et al., 2014 [10] showed a significant reduction in native grape yeast populations and faster fermentation kinetics in wines from microwave treatment of crushed grapes. ...
... Although some studies support the efficiency of microwaves [37], others oppose the concept [38,39]. The destruction of various pathogens such as E. coli and Staphylococcus aureus has been observed under microwave treatment at high-power conditions [34]. However, microwaves have shown a resonant-like effect on the growth of some yeasts, including Saccharomyces cerevisiae, increasing the yeast growth, which was not dependent on the amount of absorbed energy from the microwaves [40]. ...
... Microwave treatment achieves greater extraction of grape compounds used as nutrients by yeast, which could accelerate the fermentation process. Additionally, morphological and metabolic changes in yeast cells induced by MWs could cause activation of the yeasts after treatment [34]. by production of aromatic esters and liberation compounds of interest after lysis [35,44]. ...
Full-text available
The objective of this study was to evaluate the effect of microwave treatment of crushed grapes on the yeast population of the must and on the development of alcoholic fermentation, as well as on the extraction of different compounds from the grapes such as polysaccharides and amino acids that can affect the organoleptic quality and stability of the wine. This study demonstrated for the first time the effect of the microwave treatment of grapes on native yeast species and their diversity, producing an increase in fermentation kinetics and a decrease in the lag phase. The microwave treatment produced a positive effect on the extraction of amino acids and polysaccharides from the grapes, resulting in significantly higher amounts of the main amino acids of the must and some major volatile compounds in the treated samples. The polysaccharides most affected by the microwave treatment were the PRAGs, the main polysaccharides liberated from grapes during the maceration.
... One option is microwave radiation. Microwaves are a form of non-ionising electromagnetic radiation with frequencies ranging between 0.3 and 300 GHz and wavelengths between 1 mm and 1 m (Jones et al. 2013;Jankovic et al. 2014). Microwave ovens operate at radiation frequencies of 900 and 2 450 MHz (Meredith 1998;Jankovic et al. 2014). ...
... Microwaves are a form of non-ionising electromagnetic radiation with frequencies ranging between 0.3 and 300 GHz and wavelengths between 1 mm and 1 m (Jones et al. 2013;Jankovic et al. 2014). Microwave ovens operate at radiation frequencies of 900 and 2 450 MHz (Meredith 1998;Jankovic et al. 2014). Microwave radiation has thermal and non-thermal effects upon living organisms. ...
... Both effects are dependent on the extent of the radiation absorption, on the dielectric constant and on the electrical conductivity of the target material. Its disintegration effect is time-dependent with the cell damage being directly proportional to the exposure time of the cells to the radiation (Jankovic et al. 2014). The thermal effect of microwave radiation is the consequence of its absorption by cell molecular structures causing them to vibrate and produce heat. ...
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Citation: Pijacek M, Bzdil J, Bedanova I, Danihlik J, Moravkova M (2021): The inhibiting effect of microwave radiation on Paenibacillus larvae spores suspended in water. Vet Med-Czech 66. Abstract: The aim of this paper was to investigate the effects of microwave radiation on the viability of Paeniba-cillus larvae spores and to study the relationship between the microwave power consumption, the exposure time and the number of spores in the examined suspensions. Sterile distilled water suspensions were made using larval detritus, to contain tens, hundreds and thousands of spores. The suspensions of all the dilutions were gradually exposed to a microwave radiation power of 170, 510 and 850 W. In all the cases, the exposure time was 1, 2, 3, 4, 5, 10, 15, 20, 25 and 30 minutes. After cooling, 0.1 ml of each exposed suspension was inoculated onto three modified MYP (mannitol egg yolk polymyxin) agar plates and incubated aerobically at 37 ± 1 °C for 120 hours. The statistical evaluation of the spore counts decreasing with time was performed with the use of the nonpara-metric Friedman's variance test using the Unistat Statistical Package v6.5. The results showed that the rate of devi-talisation of the spores is dependent on the microwave oven power consumption, but independent of the number of spores. Using a power consumption of 170, 510 and 850 W, the devitalisation of the spores occurred after 15, 3 and 2 min of exposure, respectively.
... It has also been used in laboratory settings for pharmaceutical glass vials, culture media, or clinical specimens sterilization (Akşen et al., 2004). The thermal effect mechanism is based on the absorption of microwave heat energy by the cell constituents, which leads to fast vibrations of cell membrane lipids resulting in the emergence of pores (Jankovic et al., 2014). These pores may cause leakage of vital intracellular molecules being able to cause cell death (Jankovic et al., 2014). ...
... The thermal effect mechanism is based on the absorption of microwave heat energy by the cell constituents, which leads to fast vibrations of cell membrane lipids resulting in the emergence of pores (Jankovic et al., 2014). These pores may cause leakage of vital intracellular molecules being able to cause cell death (Jankovic et al., 2014). High temperatures denature cellular biomolecules such as proteins, which may also be a reason of cells lysis (Karni et al., 2013). ...
... This causes disarrangement of cell membrane and disruption of cell wall structures by destroying the lipopolysaccharides and peptidoglycan of the cell surface. This results in the emergence of pores, cell aggregations, cytoplasmic proteins aggregation, and changes of membrane permeability (Jankovic et al., 2014;Zeng et al., 2014), explaining why biomolecules such as proteins or nucleic acids (Woo et al., 2000) are detected in the extracellular fraction. ...
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The dissemination of DNA and xenogenic elements across waterways is under scientific and public spotlight due to new gene-editing tools, such as do-it-yourself (DIY) CRISPR-Cas kits deployable at kitchen table. Over decades, prevention of spread of genetically modified organisms (GMOs), antimicrobial resistances (AMR), and pathogens from transgenic systems has focused on microbial inactivation. However, sterilization methods have not been assessed for DNA release and integrity. Here, we investigated the fate of intracellular DNA from cultures of model prokaryotic (Escherichia coli) and eukaryotic (Saccharomyces cerevisiae) cells that are traditionally used as microbial chassis for genetic modifications. DNA release was tracked during exposure of these cultures to conventional sterilization methods. Autoclaving, disinfection with glutaraldehyde, and microwaving are used to inactivate broths, healthcare equipment, and GMOs produced at kitchen table. DNA fragmentation and PCR-ability were measured on top of cell viability and morphology. Impact of these methods on DNA integrity was verified on a template of free λ DNA. Intense regular autoclaving (121°C, 20 min) resulted in the most severe DNA degradation and lowest household gene amplification capacity: 1.28 ± 0.11, 2.08 ± 0.03, and 4.96 ± 0.28 logs differences to the non-treated controls were measured from E. coli, S. cerevisiae, and λ DNA, respectively. Microwaving exerted strong DNA fragmentation after 100 s of exposure when free λ DNA was in solution (3.23 ± 0.06 logs difference) but a minor effect was observed when DNA was released from E. coli and S. cerevisiae (0.24 ± 0.14 and 1.32 ± 0.02 logs differences with the control, respectively). Glutaraldehyde prevented DNA leakage by preserving cell structures, while DNA integrity was not altered. The results show that current sterilization methods are effective on microorganism inactivation but do not safeguard an aqueous residue exempt of biologically reusable xenogenic material, being regular autoclaving the most severe DNA-affecting method. Reappraisal of sterilization methods is required along with risk assessment on the emission of DNA fragments in urban systems and nature.
... On the other hand, nonthermal effects include changes in cell morphology and cell wall alterations or an enhanced protein or enzyme activity [8,21,22]. Still, the understanding of how microwaving affects microorganism is limited and a field of active research [20,23]. ...
... Microwave treatment of biological tissue causes thermal and nonthermal effects due to microwave radiation [23]. The data presented in this paper provides evidence that regularly microwaving also influences microbial community composition as well as functional profiles. ...
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Kitchen sponges massively absorb and spread microorganisms, leading to contamination of kitchen appliances, surfaces, and food. Microwaving as an effective and widespread technique can rapidly reduce the microbial load of kitchen sponges. However, long-term effects of such treatments are largely unknown. Notably, it has been speculated that regularly applied domestic cleaning and disinfection may select for microbial communities with a higher pathogenic potential and/or malodorous properties. In this study, we distributed newly purchased polyurethane kitchen sponges to 20 participants, with the instruction to use them under normal household conditions for four weeks. Ten of the participants sanitized their sponges regularly by a standardized microwaving protocol, while the remaining ten sponges remained untreated. Metagenomic sequence data evaluation indicated that, in addition to bacteria, viruses, eukaryotes, and archaea were also part of the kitchen sponge microbiome. Comparisons of sanitized and untreated kitchen sponges indicated a trend towards a reduced structural microbial diversity while functional diversity increased. Microwave sanitization appeared to alter composition and metabolic properties of the microbial communities. Follow-up studies will have to show whether these changes are more positive or negative in terms of domestic hygiene, human health, and well-being.
... Research showed that microwave treatment reduced total bacteria coliforms and a yeast population (Brettanomyces bruxellensis) in oak wine barrels, as well as minimizing preservative use [68]. A study by Slobodan et al. [69] also Figure 4: Weight of extracts obtained from the tea bags in the extraction procedure. "1" indicates one tea bag (2 g) and "2" indicates two tea bags (4 g). ...
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Elimination of microorganisms from herbal products has been a major concern due to its implicated health risk to consumers. Drying of herbal materials has been employed for centuries to reduce the risk of contamination and spoilage. )e present study adopted three drying approaches in an attempt to eliminate microorganisms from Lippia multiflora tea bag formulation. )is study also evaluated the tea bags and optimized the extraction procedure. )e L. multiflora leaves for tea bagging were air-dried and milled (A), oven-dried and milled (B), and microwaved (the milled air-dried leaves) (C). )e moisture contents were determined at 105°C ± 2°C for 2 hours to constant weight. Phytochemical parameters such as phytochemical constituents, total water extractive, and pH were assessed. )e microbial safety and quality of the L. multiflora tea bags were evaluated using the British Pharmacopoeia 2019 specifications. )e uniformity of the mass of the formulated tea bags was also determined. Extraction from the Lippia tea bags was optimized. )e results showed that using the approaches (A, B, and C) adopted for drying and processing, the moisture contents of the formulated tea bags were in the range of 9.75–10.71% w/w. All the formulated tea bags contained reducing sugars, phenolic compounds, polyuronides, flavonoids, anthracenosides, alkaloids, saponins, and phytosterols. )e pH range of the formulations was 7.11–7.54, whereas the total water extractive values were in the range of 19.12–20.41% w/w. )e one-way analysis of variance demonstrated no significant difference in the data obtained from the results from A, B, and C. )e formulation from A was found to be unsafe for consumption due to unacceptable microbial contamination limits. Microbial load of the formulations from B and C were within the BP specifications. All the batches of the formulations passed the uniformity of mass test. An optimized extraction procedure was obtained when one tea bag was extracted in 250 mL of hot water within the specified time. L. multiflora leaves meant for tea bagging should be oven-dried or microwaved before tea bagging for safe consumption.
... The intermediate frequency (IF) bandwidth was set to 300 Hz to minimize the broadband noise, and the number of points was selected as 6401 to increase the sampling resolution. The output power of the VNA was set to 0 dBm i.e. 1 mW which was sufficiently low to have no impact on the growth of E. coli through adverse effects just as joule heating 68,69 . The VNA was triggered to measure the reflection coefficient (S11 dB) every two minutes using an automated LabVIEW program made in-house. ...
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Infection diagnosis and antibiotic susceptibility testing (AST) are pertinent clinical microbiology practices that are in dire need of improvement, due to the inadequacy of current standards in early detection of bacterial response to antibiotics and affordability of contemporarily used methods. This paper presents a novel way to conduct AST which hybridizes disk diffusion AST with microwave resonators for rapid, contactless, and non-invasive sensing and monitoring. In this research, the effect of antibiotic (erythromycin) concentrations on test bacterium, Escherichia coli (E. coli) cultured on solid agar medium (MH agar), are monitored through employing a microwave split-ring resonator. A one-port microwave resonator operating at a 1.76 GHz resonant frequency, featuring a 5 mm 2 sensitive sensing region, was designed and optimized to perform this. Upon introducing uninhibited growth of the bacteria, the sensor measured 0.005 dB/hr, with a maximum change of 0.07 dB over the course of 15 hrs. The amplitude change decreased to negligible values to signify inhibited growth of the bacteria at higher concentrations of antibiotics, such as a change of 0.005 dB in resonant amplitude variation while using 45 µg of antibiotic. Moreover, this sensor demonstrated decisive results of antibiotic susceptibility in under 6 hours and shows great promise to expand automation to the intricate AST workflow in clinical settings, while providing rapid, sensitive, and non-invasive detection capabilities.
... The output power of the VNA was set to 0 dB i.e. 1mW. As the input power was sufficiently low, it had no impact on bacterial growth [71]. Furthermore, the intensity of the power radiated from the sensitive region of the resonator was measured using a handheld RF spectrum analyzer and was found to be below -70 dB, which ascertained that the power radiated at resonance had minimal to no impact on the operation of nearby electronic devices. ...
A real-time and label-free microstrip sensor capable of detecting and monitoring subsurface growth of Escherichia coli (E. coli) on solid growth media such as Luria-Bertani (LB) agar is presented. The microwave ring resonator was designed to operate at 1.76 GHz to detect variations in the dielectric properties such as permittivity and loss tangent to monitor bacterial growth. The sensor demonstrated high efficiency in monitoring subsurface dynamics of E. coli growth between two layers of LB agar. The resonant amplitude variations (Δ Amplitude (dB)) were recorded for different volumes of E. coli (3 µL and 9 µL) and compared to control without E. coli for 36 hours. The control showed a maximum amplitude variation of 0.037 dB, which was selected as a threshold to distinguish between the presence and absence of E. coli growth. The measured results by sensors were further supported by microscopic images. It is worth noticing that the amplitude variations fit well with the Gompertz growth model. The rate of amplitude change correlating bacteria growth rate was calculated as 0.08 and 0.13 dB/hr. for 3 µL and 9 µL of E. coli, respectively. This work is a proof of concept to demonstrate the capability of microwave sensors to detect and monitor subsurface bacterial growth.
... The intensity of the pyrolysis process is probably related to the electromagnetic field strength, its frequency, wave type, modulation, and exposure time. In addition, recent research has provided more evidence for the specific effects of microwaves, e.g., on the biological structures of microbial cells, which have so far been frequently considered as the effects of a thermal factor [103,104]. Therefore, it appears that changes in food under microwave heating, including the AA formation, should not be considered only as a result of the thermal factor, but also other factors that cause intensification of changes in food. Since the mechanism of these reactions is not clear, further research is needed to better understand the formation of acrylamide during microwave heating. ...
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Acrylamide (AA) is a neurotoxic and carcinogenic substance that has recently been discovered in food. One of the factors affecting its formation is the heat treatment method. This review discusses the microwave heating as one of the methods of thermal food processing and the influence of microwave radiation on the acrylamide formation in food. In addition, conventional and microwave heating were compared, especially the way they affect the AA formation in food. Available studies demonstrate differences in the mechanisms of microwave and conventional heating. These differences may be beneficial or detrimental depending on different processes. The published studies showed that microwave heating at a high power level can cause greater AA formation in products than conventional food heat treatment. The higher content of acrylamide in microwave-heated foods may be due to differences in its formation during microwave heating and conventional methods. At the same time, short exposure to microwaves (during blanching and thawing) at low power may even limit the formation of acrylamide during the final heat treatment. Considering the possible harmful effects of microwave heating on food quality (e.g., intensive formation of acrylamide), further research in this direction should be carried out.
Carrot pickle is a traditional fermented food produced all over the world. The continuous fermentation during marketing and storage resulting in over acidification, softening, undesirable aroma, and color. This study was conducted to develop fermented vegetable pickle from carrot added with spices and salt (3.5%). The aim of the study was to investigate the effect of treatments such as microwave heating for 2.5, 3.5 and 4.5 min and sodium benzoate at concentrations 350, 450 and 550 ppm on desirable quality attributes such as microbial load (log10 cfu/gm, texture, Acidity (% lactic acid), pH, LABs and sensory attributes of fermented carrot pickle during storage period of 30 days. Results indicate that microwave treated samples showed decrease in pH value from 5.68 to 4.83, 5.75 to 4.85 and 5.63 to 4.34, respectively. Microwave treated carrot pickle also showed significantly lower microbial count and titratable acidity value than samples treated with sodium benzoate. Texture analysis also showed decrease in pickle firmness during storage, but sodium benzoate treated samples showed highest decline than microwave treated samples. Color analysis showed increase in L* value in all treated samples during entire storage than control. Sensory evaluation indicated significantly higher overall acceptability score for microwave treated sample (2.5 min) than control. From the present findings it is conclude that microwave treatment could be employed to extend the shelf life and preserve the organoleptic attributes of carrot pickle.
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This study evaluates the effect of microwave treatment in grape maceration at laboratory scale on the content of free and glycosidically bound varietal compounds of must and wines and on the overall aroma of wines produced with and without SO2. The volatile compounds were extracted by solid phase extraction and analyzed by gas chromatography–mass spectrometry, carrying out a sensory evaluation of wines by quantitative descriptive analysis. Microwave treatment significantly increased the free and bound fraction of most varietal compounds in the must. Wines from microwave maceration showed faster fermentation kinetics and shorter lag phase, resulting in an increase in some volatile compounds of sensory relevance. The absence of SO2 caused a decrease in concentration of some volatile compounds, mainly fatty acids and esters. The sensory assessment of wines from microwave treatment was higher than the control wine, especially in wines without SO2, which had higher scores in the “red berry” and “floral” odor attributes and a more intense aroma. This indicates that the pre-fermentative treatment of grapes with microwaves could be used to increase the wine aroma and to reduce the occurrence of SO2.
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To investigate putative biological damage caused by GSM mobile phone frequencies by assessing electromagnetic fields during mobile phone working. Neuron-like cells, obtained by retinoic-acid-induced differentiation of human neuroblastoma SH-SY5Y cells, were exposed for 2 h and 4 h to microwaves at 1800 MHz frequency bands. Cell stress response was evaluated by MTT assay as well as changes in the heat shock protein expression (Hsp20, Hsp27 and Hsp70) and caspase-3 activity levels, as biomarkers of apoptotic pathway. Under our experimental conditions, neither cell viability nor Hsp27 expression nor caspase-3 activity was significantly changed. Interestingly, a significant decrease in Hsp20 expression was observed at both times of exposure, whereas Hsp70 levels were significantly increased only after 4 h exposure. The modulation of the expression of Hsps in neuronal cells can be an early response to radiofrequency microwaves.
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To determine the most effective method to kill Streptococcus mutans on contaminated toothbrushes. Seven toothbrushes (one for each treatment and the control) were contaminated with S. mutans. Toothbrushes were then rinsed in phosphate buffered saline (PBS) and treated as follows: (1) control without treatment; (2) air dry for 4 hours; (3) Crest Pro-Health mouthwash for 20 minutes; (4) Listerine mouthwash for 20 minutes; (5) normal cleaning cycle in a dishwasher; (6) microwave on high power for 5 minutes; and (7) ultraviolet light using the DenTek Toothbrush Sanitizer for 10 minutes. All toothbrushes were rinsed again with PBS. The bristles were cut and vortexed in PBS. Serial dilutions were performed and the number of colonies enumerated after incubation. The experiment was independently repeated seven times. The Crest Pro-Health mouthwash and the dishwasher almost completely eliminated S. mutans. The second most effective treatment was the microwave. The Listerine mouthwash and the air dry groups were not significantly different from each other and ranked third. Although UV light significantly decreased the number of bacteria compared to the control, reduction in the number of S. mutans CFU was significantly lower than that of all the other treatments evaluated. Crest Pro-Health mouthwash for 20 minutes and a normal dishwasher cycle are the most effective methods to eradicate S. mutans from contaminated toothbrushes. Dent
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Skin protects itself against infection through a variety of mechanisms. Antimicrobial peptides (AMPs) are major contributors to cutaneous innate immunity, and this system, combined with the unique ionic, lipid, and physical barrier of the epidermis, is the first-line defense against invading pathogens. However, recent studies have revealed that our skin's innate immune system is not solely of human origin. Staphylococcus epidermidis, a major constituent of the normal microflora on healthy human skin, acts as a barrier against colonization of potentially pathogenic microbes and against overgrowth of already present opportunistic pathogens. Our resident commensal microbes produce their own AMPs, act to enhance the normal production of AMPs by keratinocytes, and are beneficial to maintaining inflammatory homeostasis by suppressing excess cytokine release after minor epidermal injury. These observations indicate that the normal human skin microflora protects skin by various modes of action, a conclusion supported by many lines of evidence associating diseases such as acne, atopic dermatitis, psoriasis, and rosacea with an imbalance of the microflora even in the absence of classical infection. This review highlights recent observations on the importance of innate immune systems and the relationship with the normal skin microflora to maintain healthy skin.
Aims: To investigate the sporicidal mechanisms of microwave irradiation on Bacillus licheniformis spores. Methods and Results: We measured spore viability and the release of DNA and proteins, and performed transmission electron microscopy (TEM). A microwave oven (0·5 kW) was modified to output power at 2·0 kW, which allowed a shorter sterilization cycle. A 2·0 kW microwave treatment at the boiling temperature for 1 min did not kill all spores, but killed most spores. The spore inactivation rate was faster than that of boiling and 0·5 kW microwave oven. In contrast to boiling and 0·5 kW microwave treatments, the 2·0 kW microwave resulted in significant leakage of proteins and DNA from spores due to injury to the spore structure. TEM revealed that 2·0 kW microwave irradiation affected spore cortex hydrolysis and swelling, and ruptured the spore coat and inner membrane. Conclusions: These results suggest that 2·0 kW microwave irradiation ruptures the spore coat and inner membrane, and is significantly different from boiling. Significance and Impact of the Study: This study provides information on the sporicidal mechanisms of microwave irradiation on B. licheniformis spores.
Purpose: This study evaluated the effectiveness of different exposure times of microwave irradiation on the disinfection of a hard chairside reline resin. Materials and methods: Sterile specimens were individually inoculated with one of the tested microorganisms (Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and Bacillus subtilis) and incubated for 24 hours at 37 degrees C. For each microorganism, 10 specimens were not microwaved (control), and 50 specimens were microwaved. Control specimens were individually immersed in sterile saline, and replicate aliquots of serial dilutions were plated on selective media appropriate for each organism. Irradiated specimens were immersed in water and microwaved at 650 W for 1, 2, 3, 4, or 5 minutes before serial dilutions and platings. After 48 hours of incubation, colonies on plates were counted. Irradiated specimens were also incubated for 7 days. Some specimens were prepared for scanning electron microscopic (SEM) analysis. Results: Specimens irradiated for 3, 4, and 5 minutes showed sterilization. After 2 minutes of irradiation, specimens inoculated with C. albicans were sterilized, whereas those inoculated with bacteria were disinfected. One minute of irradiation resulted in growth of all microorganisms. SEM examination indicated alteration in cell morphology of sterilized specimens. The effectiveness of microwave irradiation was improved as the exposure time increased. Conclusion: This study suggests that 3 minutes of microwave irradiation can be used for acrylic resin sterilization, thus preventing cross-contamination.
Cryptosporidium parvum oocysts have been found on the surface of vegetables in both developed and developing countries. C. parvum can contaminate vegetables via various routes, including irrigation water. This study investigated the effect of individual treatments of chlorine, blanching, blast freezing, and microwave heating, as well as combined treatments of chlorine and freezing, and chlorine and microwave heating on the viability of C. parvum oocysts inoculated on green peppers. The viability of the oocysts after the treatments was assessed using propidium iodide and a flow cytometer. Based on the propidium iodide staining, the chlorine treatments did not affect the viability of the oocysts. Blast freezing significantly inactivated 20% of the oocysts. Microwave heating and blanching significantly inactivated 93% of oocysts. Treatment with chlorine followed by blast freezing did not affect the viability of the oocysts significantly. Treatment with chlorine and microwave heating was significantly more effective than microwave heating alone and inactivated 98% of the oocysts. The study indicates that C. parvum oocysts are sensitive to heat and, to some extent, to blast freezing, but are resistant to chlorine. Therefore, the use of chlorine during vegetable processing is not a critical control point for C. parvum oocysts, and the consumption of raw or minimally processed vegetables may constitute a health risk as C. parvum oocysts can still be found viable on ready-to-eat, minimally processed vegetables.
Microwave has nonthermal effects on enzymatic reactions, mainly caused by the polarities of the solvents and substrates. In this experiment, a model reaction with caprylic acid and butanol that was catalyzed by lipase from Mucor miehei in alkanes or arenes was employed to investigate the nonthermal effect in nonaqueous enzymatic esterification. With the comparison of the esterification carried by conventional heating and consecutive microwave irradiation, the positive nonthermal effect on the initial reaction rates was found substrate concentration-dependent and could be vanished ostensibly when the substrate concentration was over 2.0 mol L(-1). The polar parameter log P well correlates the solvent polarity with the microwave effect, comparing to dielectric constant and assayed solvatochromic solvent polarity parameters. The log P rule presented in conventional heating-enzymatic esterification still fits in the microwaved enzymatic esterification. Alkanes or arenes with higher log P provided positive nonthermal effect in the range of 2 ≤ log P ≤ 4, but yielded a dramatic decrement after log P = 4. Isomers of same log P with higher dielectric constant received stronger positive nonthermal effect. With lower substrate concentration, the total log P of the reaction mixture has no obvious functional relation with the microwave effect.
A standardized and smooth protocol for solid-phase glycopeptides synthesis under microwave irradiation was developed. Double activation system was proved to allow for highly efficient coupling of Tn-Ser/Thr and bulky core 2-Ser/Thr derivatives. Versatility and robustness of the present strategy was demonstrated by constructing a Mucine-1 (MUC1) fragment and glycosylated fragments of tau protein. The success of this approach relies on the combination of microwave energy, a resin consisting totally of polyethylene glycol, a low excess of sugar amino acid and the "double activation" method.
Although there are many product claims that address the issue of denture sanitization, controlled scientific studies on previously worn dentures have not been performed. The purpose of this study was to evaluate procedures directed at sanitizing previously worn contaminated dentures from two regions of the United States. This study examined 51 previously worn dentures from two regions. An established method of denture retrieval, sectioning, and culturing was used, including isolation of anaerobes. Evaluation of microbial contamination posttreatment was used to determine the effects of soaking dentures in Polident (US and European formulations) for varying periods of times/temperatures, microwaving dentures with varying temperatures, sonicating dentures, and immersing the dentures while using a vacuum. A combination of analysis of variance (ANOVA) and general linear model (GLM) of the SPSS was used to analyze the data with P < .05 being considered statistically significant when using a two-tailed test. While all Polident treatments were found to significantly reduce microorganism loads in dentures, extended soaking (8 hours) and 65 degrees C (5 minutes) were the most effective. Microwaving was slightly more effective than either sonication or vacuum. Regardless the treatment, dentures underwent sanitization rather than sterilization. Denture-borne microorganisms can be significantly reduced by using a Polident solution for 8 hours at room temperature or for 5 minutes at 65 degrees C. Microwaving, sonication, and use of a vacuum were less effective. ClLINICAL IMPLICATIONS The importance of daily use of Polident solution for 8 hours or for 5 minutes at 65 degrees C to sanitize worn prostheses must be stressed.