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Keywords: Garlic, Allicin, Antimicrobial, Biofilm, Quorum sensing.
Accepted on 12 April, 2021
Introduction
History revealed that Central Asian soil is the origin of garlic.
Afterwards, it has been expanded to west, south, and then
finally in east. The mother land of garlic is said to be as Middle
and West Asia. Garlic, a vegetable used for seasoning, contains
a diverse range of phytochemicals having strong curative and
antimicrobial characteristics. It is of great therapeutic
importance and finds its place in numerous foods particularly
meat ones because of its sharp odor, bitter taste, appetizer
property and gives flavor to them. Bioactive compounds like
allian, diallyl sulfide, alliin, ajonene render garlic their
miraculous properties [1]. Polyphenols is a diverse group of
complex chemical compounds with unique and extraordinary
potential to act as antioxidant chain-breaker. These biologically
active entities have the ability to shield against the damages
caused by free radicals to DNA, cellular membrane and internal
cell components. Further they exhibit antibacterial,
antiallergenic, antithromobotic and anti-arthrogenic effects.
These compounds have been found effective against pathogenic
microorganisms like Escherichia coli, Staphylococcus aureus,
Salmonella typhi, Listeria monocytogenes, Candida albicans,
Torulopsis glabrata, Vesicular stomatitis virus responsible for
numerous ailments in human body. In addition to it, these
bioactive compounds reduce oxidative stress in body,
preventing tumor formation, stimulate vasodilation and
improve insulin secretion (Figure 1) [2].
Figure 1.
Graphical Abstract-The effects of these bioactive
compounds on pathogenic microorganism.
Garlic: A Natural Therapeutic Herb
In the past few years, treatment of infectious diseases has
become an alarming global concern due to proliferation of
Mini Review https://www.alliedacademies.org/food-technology-and-preservation/
J Food Technol Pres 2021 Volume 5 Issue 4
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Figure 1.
Garlic: A natural shield against detrimental effect of microorganisms.
1Department of Food Science and Technology, Khwaja Freed University of Engineering and Technology, Rahim Yar
Khan 64200, Pakistan
2Department of Food Science and Technology, Government College Women University, Faisalabad 38000, Pakistan
Abstract
Garlic has a greater antimicrobial potential than other members of its family, due to its diverse profile
of antimicrobial compounds, among which the most renowned are allicin, diallyl polysulfides and ajoenes. A unique
Sulphur based compound allicin, found most abundantly in raw garlic. Exhibits antimicrobial potential and has been
found equally effective against both gram-positive as well as,
gram-negative bacteria. Allicin has the potential to hinder the bacterial biofilm formation, which is the leading cause of
microbial resistance against antibiotic treatment leading chronic infections. Allicin eradicate biofilms by disrupting
quorum sensing in microorganisms. Other bioactive compounds also exhibit similar inhibitory effects on
microorganisms. These biological characteristics of garlic and
garlic derived bioactive compounds can be used to intensify the effects of existing drugs and can also
be used for the treatment of infections. In this review, we will summarize the effects of these bioactive compounds on
pathogenic microorganism.
Atif Liaqat*1, Muhammad Farhan Jahangir Chughtai1, Kanza Saeed1, Adnan Khaliq1, Tariq Mehmood1, Samreen Ahsan1,
Rabia Iqbal2
drug-resistant bacteria. In order to treat infectious diseases new
generation antibiotics are continuously being developed, and
are part of infectious diseases treatment strategies; however,
the increased microbial adaptability with extensive and
uncontrolled use of such antibiotics has led to resistance in
bacteria, leading to escalated drug-resistant ability attained
through drug-target molecules mutations, cell membrane
compositional changes, the efflux pumps overexpression,
metabolizing enzymes production and biofilm formation [3].
Among all the above mention mechanisms, the biofilm
comprises a large aggregated community of microbial cells
protected by complex matrix, enabling the microbial cells to
resist the detrimental effects of soldiers attack in our body
(natural immunity) and antibiotics.
Allium sativum has long been used as a natural remedy against
infectious maladies. Commonly known as garlic, has long been
used as a natural remedy against infectious maladies [4].
Allicin is a chemically unstable compound and quickly
vanishes once it comes into direct contact with human body
plasma. Thus, making it troublesome for allicin to reach the
target infected sites of the body in an active and effective form.
Recent studies have proved that garlic derived sulfur-
containing compounds, like Diallyl Disulfide (DAS2) and
ajoene, restrict biofilm formation by restraining microbial
communication signals (Quorum Sensing). Although, there are
few studies which show that antimicrobial potential of these
bioactive compounds is not as effective in comparison to the
medical antibiotics utilized in clinical settings [5,6]. Numerous
studies support the fact that herbs and their derivative bioactive
compounds not only exert inhibitory effect on biofilm
generation, but also have antibiotic activity [7].
Allicin
In raw garlic, allicin is the most profound characteristic sulfur-
containing compound. It is an alliin derived compound. There
are numerous research references that support that allicin is a
broad-spectrum antimicrobial that has been found to be
effective against Gram-positive and negative bacteria. It also
has deadly impact against multidrug-resistant bacteria [8]. In
addition to it, allicin exhibits anti-parasitic, antiviral, and anti-
fungal potential [9]. Allicin exhibits antimicrobial activity
through the mechanism of S-allylmercapto recasting of thiol-
containing proteins, which ultimately leads to the initiation of
lethal events, like glutathione level drop, the induction of
protein aggregation and crucial enzymes inactivation [10].
Vaporized allicin exhibited strong antimicrobial activity against
pathogenic bacteria responsible for lungs infection [11].
Additionally, topical application of allicin has proved to
effectively kill methicillin-resistant S. aureus stains (MRSA)
leading to improved treatment of skin infection.
Mode of Action and Antimicrobial Properties
A broad-spectrum biocide, allicin has been found effective in
killing microbial as well as malfunctioned human cells. It is
highly reactive thiosulfinate with the ability to oxidise thiol
groups, the nature of the reaction is similar to the thiol-
disulfide exchange mechanism. The oxidation of thiol group
results in the formation of adduct S-thioallyl and the entire
procedure is regardsed as S-thioallylation [12]. In stage 2, the
adduct reacts with a second thiol group of protein resulting in
the formation of disulfide bridge. Residual S-thioallyl
transforms into allylmercaptane. High molecular weight
protein thiols and low molecular weight glutathione both are
targeted by S-thioallylation. S-mercaptoglutathione
(thioallylated glutathione) a substrate for the enzyme
glutathione reductase is unable to act as an oxidation-reduction
buffer, but it recycles S-mercaptoglutathione to
allylmercaptane and glutathione through an NADPH mediated
reaction [13]. Consequently, the shunt pathway which is a key
source of NAPDH in cellular metabolism is pivotal to resist
against allicin, rendering it the ability to control cellular growth
[14].
According to a study [15] regarding antibacterial potential of
solo garlic to evaluate it against E. coli, S. aureus, solo black
garlic was found to be effective particularly when it is
fermented for about a month prior use. In another 8 days
storage study of ground pork, activity of garlic against
coliforms and Pseudomonas spp. was evaluated and positive
results of fresh garlic, dehydrated garlic and garlic essential oil
were recorded [16]. In a study regarding development of
polylactic acid active film containing extracts of wild garlic
and its antimicrobial potential against E. coli and S. aureus,
results proved that polylactic acid film with natural extracts
retards the growth of foodborne pathogenic bacteria [17]. Gao
et al. (2019) used traditional Chinese laba garlic and isolated
three antimicrobial fractions from it. Activity was tested
against E. coli and S. aureus growth and the results proved that
peptides isolated from Laba garlic possess promising
antimicrobial potential comparable to antibiotics [18].
Effects on Quorum Sensing (QS) and Biofilm
Formation
Bacteria have a barricade system also known as biofilm
formation, which restrain the entry of disinfectants, host
immune molecules and antibiotics into the bacterial cell
membrane. This is a leading cause of induced drug-resistance
of microbial cells [19]. Additionally, Quorum Sensing
molecules, like N-Acyl homoserine lactone mediate
intercellular communication for biofilm formation by bacterial
population. In order to inhibit biofilm formation, we need to
understand the underlying mechanism of microbial Quorum
Sensing. Various studies have been conducted about
exploration of natural products that could be an effective
remedy against biofilm formation. Omid et al., have screened
few components from garlic extract to identify Qs Inhibitors
(QSIs) that effectively inhibited biofilm formation. Mechanism
involved in the process comprises prevention of biofilm
formation by hindering initial bacterial adhesion and secretion
of extracellular polymeric substances [20]. In addition to
regulate Quorum Sensing allicin halts the release of virulence
factors [21]. Similarly, ajoene blocks virulence factors
production induced by Quorum Sensing, resulting in inhibition
of biofilm formation [22]. Diallyl disulfide inhibits the
Citation: Liaqat A,Chughtai M F J,Iqbal R et al.Garlic, a natural shield against detrimental effect of microorganisms.J Food Technol Pres
2021;5(4):1-7.
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J Food Technol Pres 2021 Volume 5 Issue 4
Pseudomonas spp. biofilm formation by preventing the
virulence factor production through QS regulation when used
in a concentration of 0.16-1.28 mg/ml. In addition to it, diallyl
disulfide hamper the formation of biofilm by stifling the QS-
related genes expression [19]. Moreover, in case of S. aureus
biofilm formation QS system, a thioester group containing
peptidic compound acts as an autoinducer of process. Diallyl
disulfide may also inhibit microbial communication network
through reacting with the autoinducer thioester group. These
bioactive compounds contribute to mitigate the detrimental
impacts of these resistant microorganisms on human health and
food systems, these natural compounds can be expected to
transcend the problem of drug resistance development
primarily caused by biofilm formation [23].
Conclusion
Various bioactive compounds derived from garlic proved to
have broad spectrum antimicrobial potential. In particular,
allicin and its derivative compounds have been profoundly
studied for their antimicrobial activity, which have shown the
inhibitory activity against microorganisms as well as their
biofilm formation via inhibiting Quorum Sensing.
Development of stable allicin derivatives will lead to the
development of exclusive compounds with distinguished
antimicrobial activity, more potent impeding potential against
biofilm formation and eradication of drug-resistant bacteria.
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*Correspondence to
Atif Liaqat
Department of Food Science and Technology,
Khwaja Freed University of Engineering and Technology,
Rahim Yar Khan 64200, Pakistan.
E-mail: atif.liaqat@kfueit.edu.pk
Citation: Liaqat A,Chughtai M F J,Iqbal R et al.Garlic, a natural shield against detrimental effect of microorganisms.J Food Technol Pres
2021;5(4):1-7.
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