How does garlic kill bacteria

At the time they learned that garlic extract is able to inhibit bacteria, and in they showed that the sulphurous compound ajoene found in garlic is responsible for the effect. The new study, which has been published in the scientific journal Scientific Reports , takes an even closer look and documents ajoene's ability to inhibit small regulatory RNA molecules in two types of bacteria. They are called Staphylococcus aureus and Pseudomonas aeruginosa. They actually belong to two very different bacteria families and are normally fought using different methods.

But the garlic compound is able to fight both at once and therefore may prove an effective drug when used together with antibiotics', says Tim Holm Jakobsen. Previous studies have shown that garlic appears to offer the most powerful, naturally occurring resistance to bacteria. In addition to inhibiting the bacteria's RNA molecules, the active garlic compound also damages the protective slimy matrix surrounding the bacteria, the so-called biofilm. Allicin was identified as the principal ingredient of garlic that is responsible for the antibacterial activity of a wide variety of bacteria Cavallito and Bailey, a.

Allicin was found to exhibit activity against M. Vancomycin-sensitive and -resistant clinical isolates and standard strains of Enterococci species were sensitive to allicin Jonkers et al. Allicin exhibited the best anti- H. A meta-analysis of clinical data indicated that adding allicin to conventional therapy improves the eradication of H.

Allicin along with related thoisulfinates, allyl methyl, and methyl allyl thiosulfinate were found and purified from acetone garlic extract. Allicin along with allyl methyl and methyl allyl mixture exhibited activity against H. In a recent report, allicin was found to be active against C. The same group reported that allicin did not affect spore germination, but significantly inhibited spore outgrowth of C.

In vitro assay found that allicin was effective against 30 strains of Staphylococcus epidermidis including methicillin-resistant strains Perez-Giraldo et al. A stable aqueous extract of allicin was found to be effective against 30 clinical MRSA isolates, some of which were mupirocin resistant. Similarly, aqueous allicin extract and cream demonstrated anti-Lancefield group B streptococci clinical isolate using in vitro assays Cutler et al.

A comparative in vitro study of antibacterial activity against S. The results of the study indicated that fresh garlic was more potent against S. The administration of allicin to rainbow trout through its diet almost eliminated mortality when infected with Aeromonas hydrophila , a fish pathogen. In addition, in vitro studies also indicated that this bacterium was sensitive to allicin Nya et al.

It was found that A. Although an in vitro assay found that C. The possible explanation for this could be that the presence of mucus inhibited the activity of allicin in vitro Robyn et al. In an interesting study, allicin vapors were able to exhibit bactericidal activity against MDR lung pathogenic bacteria such as P.

Allicin is the most potent antibacterial organosulfur compound found in garlic. The higher activity is thought to be due to the highly reactive sulfoxide group of allicin. However, the stability and solubility of allicin are the challenges in its clinical use. Animal studies highlight the reduced bioavailability and toxicity associated with allicin administration Amagase et al. Bacterial biofilms are aggregations of bacterial cells in a matrix of extracellular polymeric substances EPS that include proteins, nucleic acids, polysaccharides, and lipids that are secreted by the bacteria.

The formation of biofilm is a complex process that involves quorum sensing QS signaling. QS is also associated with the expression and release of various virulence factors that play a major role in pathogenesis. The formation of biofilm has been strongly associated with bacterial pathogenesis and antibiotic resistance. Therefore, developing strategies to inhibit biofilm formation has been a major area of research for many years.

In addition to using synthetic antibiofilm agents, the use of many phytochemicals including garlic and its organosulfur compounds has gained a lot of interest. Table 3 lists the antibiofilm and anti-QS studies that have been performed using garlic and its compounds. AGE was found to inhibit the coagulase activity of S. GO was found to inhibit toxin production by Clostridium botulinum type A Jc et al.

Garlic ointment made by mixing GP with petroleum jelly not only prevented the formation of biofilm but also disrupted the already formed biofilm of bacteria that were isolated from burn wounds Nidadavolu et al. DAS was found to kill both planktonic and sessile C. A genetic screening system was utilized to screen many herbal and pure compounds for their QS inhibition activity, and it was found that garlic exhibited significant inhibition of QS.

Microarray transcriptome analysis indicated that the water extract of toluene extract of garlic affected the expression of virulence genes that were controlled by QS. In addition, garlic altered the in vitro biofilm to increase the penetration and killing of P.

It was also found that pretreatment of P. Bioactivity-guided fractionation of garlic extract identified ajoene as quorum sensing inhibition QSI and microarray studies revealed that it reduced the expression of few QS-controlled virulence genes of P. Similar to previous observations, pretreatment of biofilms with ajoene increased the antibacterial activity of tobramycin on biofilm-associated P.

The QSI activity of ajoene encouraged the screening of a library of compounds to identify a couple of sulfur-containing compounds that were similar to ajoene with QSI activity. Twenty-five disulfide bond-containing compounds were synthesized based on a quantitative structure—activity relationship QSAR study. These compounds could reduce the production of virulence factors, which included elastase, rhamnolipid, and pyocyanin.

Besides, they were also able to inhibit the infection of P. The motility and biofilm formation of P. Ajoene alone and in combination with ciprofloxacin significantly increased the serum sensitivity, phagocytic uptake, and killing of P. Furthermore, in the P. In addition to inhibiting production of long-chain acyl homoserine lactones, ajoene was also found to inhibit Pseudomonas quinolone signal PQS Vadekeetil et al.

Table 3. Antibiofilm, antitoxin, and anti-QS activity of garlic and its compounds. Allicin was also found to not only reduce biofilm formation of P. Relative gene expression studies indicated that it reduced the expression of many important QS and virulent genes Li et al. An interesting follow-up study performed an RNA transcriptome and proteome analysis on P.

In vitro studies found that allicin and aqueous garlic fresh and aged extract inhibited production of streptolysin O, a cytolytic toxin by all strains of group A streptococci GAS Arzanlou and Bohlooli, The transcription regulator HilA plays a crucial role in regulating the complex mechanism of Salmonella invasion, and it was found that dimethyl sulfide DMS downregulates the expression of the hilA gene and multiple virulent genes Antunes et al. The protease activity of SpeB was inhibited by allicin in vitro , and it is due to inhibition of truncation of SpeBm, the precursor protein of SpeB Arzanlou, The reduction in the production of alpha-toxin by methicillin-susceptible and -resistant S.

In addition, hla and agrA genes that regulate the production of alpha-toxin were downregulated by allicin Leng et al. Administration of allicin alone or with vancomycin significantly reduced biofilm formation by S. In vitro studies indicate that allicin exhibits antibiofilm property against S. Allicin, water, and ethanolic extract of garlic exhibited antibacterial activity on biofilm-associated bacteria.

Allicin decreased the thickness of the biofilm in a concentration-dependent manner. Gene expression studies indicated that allicin treatment of biofilm-associated bacteria resulted in downregulation of app and icaA genes that are associated with bacterial adhesion whereas only icaA was downregulated in planktonic cells Wu X. In vitro biofilm formation of S. However, allicin and chlorhexidine were cytotoxic individually, but the cytotoxicity was significantly reduced when cells were treated with the combination of both Perez-Kohler et al.

To evaluate the effect of presoaking polypropylene mesh in allicin with chlorhexidine on biofilm formation in vivo , rabbit hernia model was infected with S. In vitro assay indicated that FGE not only inhibited the formation of biofilm but also eradicated biofilms by these isolates on various surfaces. In vivo mice infection studies with P. The major organosulfur compounds of garlic, namely, allicin, ajoene, and aliphatic sulfides, pose QSI and antibiofilm activity.

These activities are most explored in P. It is evident from the data that garlic compounds downregulate QS and biofilm-associated genes. However, the precise mechanism in terms of whether the compounds bind and modify the transcription factor or interact with promoters of these genes is yet to be investigated.

In vivo studies are encouraging to test the use of these compounds in clinical testing. The combination therapy sometimes leads to a synergistic effect, which effectively lowers the dose of individual drugs. Similarly, synergistic antibacterial effects were noticed when garlic and its compounds were used in combination with other phytochemicals and antibiotics. Both garlic crude extract and pure allicin exhibited strong synergy with vancomycin against 11 VRE clinical isolates with bacteriostatic action Jonkers et al.

Raw garlic extract and commercial garlic tablets displayed synergistic effects against H. In a clinical study, administration of allicin along with standard treatment lansoprazole, clarithromycin, and amoxicillin improved the percentage of H. The combination of DATS and DATTS was either additive or synergistic when tested in combination with ceftazidime, gentamicin, imipenem, and meropenem except for DAT when used in combination with ceftazidime and gentamicin against ceftazidime and gentamicin-resistant K.

Gentamicin administration induces nephrotoxicity and few reports have indicated that co-administration of aged garlic extract, garlic, S-allyl cysteine, DAS, and DADS ameliorates this nephrotoxicity.

It was demonstrated that none of these agents decreased the activity of gentamicin; moreover, SAC, DAS, and DADS have enhanced the antibacterial activity of gentamicin, which makes them safe to use along with gentamicin to protect from nephrotoxicity Maldonado et al. The results indicate that allicin in combination with beta-lactam antibiotics results in synergy Cai et al.

The synergy of allicin with cefoperazone was confirmed against P. In the case of tobramycin, certain synergy was observed against P. It is reported that serum of patients that were administered garlic extract with standard antituberculosis had increased antitubercular activity compared to the control group, suggesting a synergistic effect when garlic is given in combination with antituberculosis drugs Gupta et al. In the P. The clearance of bacteria with ajoene alone was also significantly better compared to placebo.

In case of long-term infection, the clearing of bacterial cells was significantly improved with ajoene and tobramycin treatment compared to control. However, there was no advantage of combining ajoene to tobramycin in clearing the bacteria Christensen et al. Disk diffusion assay results indicated that the crude extract of garlic showed a synergistic effect when used in combination with gentamicin against E.

In a similar study, antibiotic-resistant P. Another study reported that the ethyl acetate extract of garlic was antagonistic to the activity of chloramphenicol Mahomoodally et al. MDR E. The zone of inhibitions of Tazma honey and garlic crude extract combination were higher than when these were used individually against common pathogenic bacteria Andualem, Garlic essential oil in combination with essential oils from several other species did not result in any synergy against tested pathogenic bacteria Bag and Chattopadhyay, The in vitro interaction studies of a combination of AGE and Manuka honey against extended-spectrum beta-lactamase-producing E.

Mechanistic studies to understand the synergistic effects of garlic with antibiotics or other chemicals are lacking. Such studies are required for encouraging the use of garlic compounds to complement conventional medicine. The principal active ingredient responsible for the antibacterial activity of garlic was identified to be allicin Cavallito and Bailey, a.

This finding was immediately followed by the observation that cysteine and other sulfhydryl-containing compounds inhibited the antibacterial activity of allicin, leading to the hypothesis that allicin might exert its antibacterial effect by reacting with sulfhydryl groups of the bacterial proteins Cavallito and Bailey, b ; Cavallito et al. Allicin would react to sulfhydryl groups of cysteines irreversibly and will not be available to react with the sulfhydryl groups of the enzymes.

The ability of allicin to inhibit various sulfhydryl enzymes indicates that the mechanism of antibacterial action of allicin is by reacting with the sulfhydryl groups of the many metabolically important bacterial enzymes Wills, The action of allicin is mostly non-specific as it is found to inhibit urease, papain, amylase, and alcohol dehydrogenase.

NMR experiments identified S -allylmercaptocysteine, confirming the reaction between allicin and sulfhydryl group of cysteine Rabinkov et al. The rapid permeability of allicin through lipid bilayers supports the idea of allicin able to reach and react with sulfhydryl groups of bacterial proteins Miron et al.

Mass spectrometry and Raman spectrum analysis confirm that allicin enters the cell rapidly and reacts with cysteine and glutathione sulfhydryl groups Fujisawa et al. The enzymatic activity of bacterioferritin comigratory protein BCP from B.

The inhibition of trypsin-like protease and general protease activity of P. Streptolysin O and mature Streptococcal pyrogenic exotoxin B of Streptococci that contain functionally important cysteines were inhibited by allicin and the addition of DTT reversed the inhibition Arzanlou and Bohlooli, ; Arzanlou, Mass spectrometric proteomic analysis of cytoplasm of E.

It was shown that allicin reacts with low-molecular-weight cellular thiols such as glutathione GSH causing oxidative stress Muller et al. Overall, these studies establish that the mechanism of antibacterial activity of allicin is by reacting with the sulfhydryl attaching allythio group through a disulfide bond.

However, it should be noted that the mechanism of action of allicin is non-specific, which could make it cytotoxic. In vivo study revealed that allicin modulates immunological parameters such as increased phagocytic and serum lysozyme activity to protect rainbow trout fish from A. Allicin is highly unstable and is degraded into various organosulfide compounds Figure 1B. The organosulfides also have been reported to show activity against a wide range of bacteria.

Different studies have shown that organosulfides constitute a majority of GO. The mechanism of action of organosulfides, like allicin, is to react with free sulfhydryl groups of enzymes. However, organosulfides are not as reactive as allicin due to the absence of oxygen that is bound to sulfur in allicin. The activity of H.

Like allicin, addition of cysteine has reduced the antibacterial activity of GO against E. A recent study established that the antibacterial activity of diallyl polysulfides is due to their ability to react with sulfhydryl groups of various enzymes of B.

These observations were consistent with the electron microscopy data that showed damage to cell wall and membrane Lu et al. Treatment of C. A global proteomic analysis was performed to determine the mechanism of the anti- H. The results of 2D gel electrophoresis of proteins showed that upon treatment with DATS, proteins involved in metabolism, biosynthesis, bacterial virulence, and redox reactions were downregulated while stress response chaperon proteins were upregulated.

A study performed RNA sequencing to study the changes in the global transcriptome of C. Although there were a large number of genes that were up- and downregulated by the DAS treatment, clusters of genes that are related to cell shape and wall maintenance and lipopolysaccharide synthesis were upregulated while RNA and amino acid biosynthetic genes were downregulated. This indicates that DAS causes injury to the cell wall and membrane and decreases general metabolism Feng et al.

The anti- C. The transcriptome analysis of C. In addition, flagellum and bacterial motility genes were downregulated, suggesting that ajoene negatively impacts biofilm formation Feng et al. Besides, some work also suggests that garlic compounds could also have a global effect on DNA, RNA, and protein synthesis.

These mechanisms are observed in both Gram-positive and Gram-negative bacteria, suggesting that garlic and its compounds use similar antibacterial mechanisms for both groups of bacteria.

However, the activity of the compounds is not specific, which could restrict their clinical application. The mechanism of action of garlic and its compound has been summarized in Figure 2. Figure 2. Illustration of the mechanism of action of garlic organosulfur compounds. Garlic organosulfur compounds exert their antibacterial activity mainly through two mechanisms: i The organosulfur compounds are highly reactive with sulfur having the capability to form disulfide bonds with the free sulfhydryl groups of proteins including enzymes.

The formation of disulfide bonds renders the enzyme inactive, resulting in the death of bacteria. This interaction compromises the integrity of the cell membranes of the bacteria leading to leakage of cell content leading to death. In addition, it is also thought that garlic organosulfur compounds interfere with protein production, DNA replication, and alter gene expression.

The emergence of various technologies such as nanotechnology, refined organic synthesis methods, and specialized drug delivery methods provide ample opportunities to use garlic organosulfur compounds as novel antibacterial agents. Green nanoparticle synthesis in recent times has emerged as a powerful tool to use phytochemicals to not only synthesize nanoparticles but also improve the antibacterial functions of these chemicals and particles Wang and Vermerris, Garlic extract has been used for the green synthesis and stabilization of silver nanoparticles.

Eco-friendly garlic-silver nanoparticles synthesized using garlic clove extract displayed a greater antibacterial and antibiofilm activity on clinically important pathogens such as MRSA and P. TSDB displayed a robust inhibitory effect against S. The increase in the levels of protein and no change in the levels of alkaline phosphate in culture upon treatment with TSDB and DATS compared to control suggest damage to the cell membrane but not so much to the cell wall Wu et al.

GO microspheres were monodispersed in water by microemulsion technique to overcome its volatile characteristics and poor aqueous solubility. The study specified that the water-dilutable microemulsion that is formed by GO encapsulated in a nanoparticle vector is effective in preventing S. In another study, wild garlic Allium ursinum L. The encapsulation led to an enhancement of the extract dissolution performance as well as an improvement in the solubility of more than fold compared to the pure extract.

Microparticles were stable over a 3-month period, showing only a minor decrease in the content of active compounds allicin and S -methyl methane thiosulfonate and upholding a good antimicrobial activity. The study suggests that such spray congealing technology can be used to improve the solubility, bioavailability, and stability of the garlic active ingredients including allicin without affecting their antibacterial properties Tomsik et al.

The stability of phytochemicals present in GO, mainly allicin, was improved when biogenic nanoscale mesoporous silicon derived from the silicon-accumulator plant Tabasheer Bambuseae was used as a potential carrier as the antibacterial activity of this material was better than GO only control Le et al.

More research should be focused to make similar nanoparticles, emulsions, and novel formulations using pure garlic compounds, mainly allicin, to improve their stability. In vitro studies with allicin aerosol and vapors using a lung model demonstrated the antibacterial efficacy of allicin with a correlation between aerosol deposition pattern and bacterial growth inhibition.

Interesting synergy was observed with allicin that was administered with ethanol against E. It was interesting to note that DAS is not a strong antibacterial compound, but when given in combination with zinc oxide nanorods as an emulsion, it displayed a synergistic effect against S. In a study, SAC, which is not antibacterial by itself, exhibited antibacterial activity when in complex with palladium II against E.

Organosulfides were converted into nano-iron sulfides with fold superior antibacterial activity against pathogenic and drug-resistant bacteria compared to compounds themselves. The nano-iron sulfides released hydrogen polysulfanes and topical application in animal models resulted in reduced biofilm formation and accelerated wound healing Xu et al.

Leontiev et al. Here, dimethyl-, diethyl-, diallyl- allicin , dipropyl-, and dibenzyl-thiosulfinates form a series of molecules with increasing molecular mass and hydrophobicity, which would be anticipated to affect physical characteristics such as rate of diffusion, volatility, and membrane permeability, all of which are expected to affect the antibacterial properties of the molecules. In this study, the more volatile compounds showed noteworthy antimicrobial properties via the gas phase.

Thiosulfinates differed in their effectivity against specific organisms, and some were thermally more stable than allicin. These results encourage the application of garlic-based compounds in medicine and agriculture either singly or in combination with other antimicrobials Leontiev et al. Attaching N -propylthiol similar chemistry to allicin to ciprofloxacin increased the sensitivity of MRSA toward ciprofloxacin, suggesting that combination chemistry with garlic organosulfur could potentiate existing antibiotics Sheppard and Long, Another study screened a chemical library composed of 19 synthesized pyridyl disulfides that emulate the chemical reactivity of allicin for antimicrobial activity against Gram-positive species including VRSA.

The study identified pyridyl disulfides as stable alternatives to allicin with a similar narrow-spectrum profile and are thought to function as pro-oxidants like that of allicin Sheppard et al. As garlic is consumed regularly all over the world, it is considered non-toxic without any side effects.

However, there are limited reports of toxic side effects of garlic and its constituents. In some individuals, contact with garlic and its constituents especially oil-soluble sulfur compounds leads to skin irritation and dermatitis Jappe et al. In vivo studies administering garlic juice resulted in stomach damage. Garlic juice rich in allicin and allicin itself cause damage to the intestinal epithelial mucosa Kodera, Allicin was also reported to immobilize sperms in vitro Qian et al.

In vitro cytotoxicity studies showed that DAS did not affect the cell growth or viability, whereas both DAS and allicin changed the morphology of cells. Allicin also significantly decreased the metabolic activity of cells Velliyagounder et al. The concentration at which these effects are noticed are relatively high and more studies need to be done to evaluate the toxicity of garlic and its compounds at concentrations that exhibit antibacterial effects.

The extensive research strongly indicates that garlic organosulfur compounds exhibit strong antibacterial activity against a wide range of bacteria including MDR strains. Although garlic organosulfur compounds have been known to be excellent antibacterial compounds, not much progress has been made in the direction of utilizing them clinically to tackle the problem of antibiotic resistance.

The toxicity data of garlic and its compounds from animal studies are inconsistent with some studies reporting no toxic effect, whereas some report inflammation and toxic effects.

The lower stability, solubility, and bioavailability of these compounds have hindered their use in the clinical setting. However, the organosulfur compounds are attractive because their bactericidal activity is exerted through multiple mechanisms, making it difficult for bacteria to develop resistance. Another concern that should be addressed for the use of garlic compounds is their toxicity and specificity to use them as antibacterial agents. Although a great deal of research has been done on the antibacterial potential of garlic and its compounds, there are recent gaps that need to be filled to utilize them as antibacterial agents in clinical settings.

The first major area where more research should be focused is to develop robust and economical extraction or synthesis procedures that would yield pure garlic compounds.

Besides, most of the organosulfur compounds of garlic are not water soluble and are unstable. Thus, formulations using advanced nanoparticle or emulsion techniques should be developed with improved solubility and self-life. A database should be created to curate the antibacterial data of garlic compounds by themselves and in combination with other antibiotics, which should be performed under pre-established guidelines.

Such a database can be used by artificial intelligence tools to predict the most effective combinations for testing or treatment. Most of the research reports the in vitro antibacterial activity of garlic compounds that are important but not necessarily translate to in vivo conditions.

Therefore, future research should be focused on validating the antibacterial activity of garlic compounds in animal infection models. Furthermore, elaborate toxicology and pharmacokinetic studies with respect to different pure organosulfur compounds, administered amount, and route should be performed. Clinical studies of garlic compounds except for anti- H. All these gaps in the research have been summarized in a cartoon Figure 3.

Recent advances in science and technology such as combinatorial and refined chemical synthesis techniques, nanotechnology, bioinformatics, computation tools, and advanced formulation can effectively overcome the challenges to develop the garlic organosulfur-based novel antibiotics. In the light of rapid emergence of antibiotic resistance, it is warranted that more research should be focused to understand the precise mechanism of action at a molecular level of organosulfur compounds.

The organosulfur compounds have the potential to make a huge impact on human health by decreasing the mortality associated with bacterial infections. Figure 3. Research in these areas will ensure the use of garlic-based novel antibacterials in the clinical setting.

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Antunes, L. Inhibition of Salmonella host cell invasion by dimethyl sulfide. Arora, D. Antimicrobial activity of spices. Agents 12, — Arreola, R. Immunomodulation and anti-inflammatory effects of garlic compounds. Arzanlou, M. Inhibition of streptococcal pyrogenic exotoxin B using allicin from garlic. Inhibition of streptolysin O by allicin - an active component of garlic. Avato, P. Allylsulfide constituents of garlic volatile oil as antimicrobial agents. Phytomedicine 7, — Aydin, A. Garlic oil and Helicobacter pylori infection.

Bag, A. Evaluation of synergistic antibacterial and antioxidant efficacy of essential oils of spices and herbs in combination. PLoS One e Bakri, I. Inhibitory effect of garlic extract on oral bacteria. Their prayers and incantations cared for the emotional state of their patients, while their poultices and tinctures worked to heal the physical ailment. Over time, coinciding with the Indo-European invasion of the Middle East and North Africa, men claimed the prestige and and medical standing women once held.

These were the women in a community called upon when the head of a poor household fell ill, or a woman began childbirth.

Unlike doctors and other medical professionals, the expertise from these women was rarely compensated. Additionally, garlic-like bulbs were used in teas to treat flu-like symptoms by indigenous North Americans.

Notably, these practices were in place long before the birth of the modern university and the associated Western medicine standards. These independent discoveries of garlic-based treatments are prime examples of robust scientific research that were reproduced by multiple cultures across the globe.

The scientific literature today, however, adds important resolution to the discovery made by anonymous scientists millennia ago. For instance, how does garlic work as an antimicrobial? Garlic has many active antimicrobial components, but allicin is the most researched.

Allicin originates from the sulfur-containing amino acid alliin in a conversion facilitated by the enzyme alliinase. Alliin and alliinase are contained in separate compartments of the garlic clove. When garlic is crushed, the 2 ingredients come together to generate allicin, a highly volatile compound that provides the lovely smell of fresh garlic.

Allicin contains sulfur amino acid groups that enable it to target thiol-containing enzymes, particularly those in non-mammalian cells. Thiol is another term for sulfhydryl groups SH , and if 2 of them are close enough when a protein is folded, they become deprotonated and form disulfide bonds.

Allicin interferes with thiols by forming disulfide bonds with protonated sulfhydryl groups, a temporary and reversible reaction that inactivates the proteins in key microbial processes such as RNA synthesis and acetyl-CoA formation.

Mammalian cells are less affected by allicin because they contain much more glutathione, a sulfhydryl antioxidant, than microbial cells. The large amounts of glutathione presumably rapidly re-protonate the affected sulfhydryl groups, putting the proteins back in action and drastically reducing allicin toxicity for mammalian cells.