Mini Review - Journal of Food Technology and Preservation (2021) Volume 5, Issue 4
Garlic: A natural shield against detrimental effect of microorganisms.
- Corresponding Author:
- Atif Liaqat
Department of Food Science and Technology
Khwaja Freed University of Engineering and Technology
Rahim Yar Khan 64200
E-mail: [email protected]
Accepted date: 12 April, 2021
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):3-6.
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.
Garlic, Allicin, Antimicrobial, Biofilm, Quorum sensing.
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 . 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) .
Garlic: A Natural Therapeutic Herb
In the past few years, treatment of infectious diseases has become an alarming global concern due to proliferation of 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 . 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 . 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 .
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 . In addition to it, allicin exhibits anti-parasitic, antiviral, and anti-fungal potential . 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 . Vaporized allicin exhibited strong antimicrobial activity against pathogenic bacteria responsible for lungs infection . 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 . 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 . 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 .
According to a study  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 . 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 . 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 .
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 . 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 . In addition to regulate Quorum Sensing allicin halts the release of virulence factors . Similarly, ajoene blocks virulence factors production induced by Quorum Sensing, resulting in inhibition of biofilm formation . Diallyl disulfide inhibits the 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 . 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 .
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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