Abstract
Garlic (Allium sativum) has potent antimicrobial activity due to allicin (diallylthiosulfinate) synthesized by enzyme catalysis in damaged garlic tissues. Allicin gives crushed garlic its characteristic odor and its volatility makes it potentially useful for combating lung infections. Allicin was synthesized (>98% pure) by oxidation of diallyl disulfide by H2O2 using formic acid as a catalyst and the growth inhibitory effect of allicin vapor and allicin in solution to clinical isolates of lung pathogenic bacteria from the genera Pseudomonas, Streptococcus, and Staphylococcus, including multi-drug resistant (MDR) strains, was demonstrated. Minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) were determined and compared to clinical antibiotics using standard European Committee on Antimicrobial Susceptibility Testing (EUCAST) procedures. The cytotoxicity of allicin to human lung and colon epithelial and murine fibroblast cells was tested in vitro and shown to be ameliorated by glutathione (GSH). Similarly, the sensitivity of rat precision-cut lung slices (PCLS) to allicin was decreased by raising the [GSH] to the approximate blood plasma level of 1 mM. Because allicin inhibited bacterial growth as a vapor, it could be used to combat bacterial lung infections via direct inhalation. Since there are no volatile antibiotics available to treat pulmonary infections, allicin, particularly at sublethal doses in combination with oral antibiotics, could make a valuable addition to currently available treatments.
Highlights
The antibacterial activity associated with garlic (Allium sativum L.) was identified by Cavallito in 1944 as being due to diallylthiosulfinate which was given the trivial name allicin [1,2]
Allicin vapor inhibited the growth of lung pathogenic bacteria over a range of concentrations
We have previously shown in agar diffusion assays that allicin compared well on a mol-for-mol basis with ampicillin and kanamycin against E. coli [35], and there have been numerous individual reports that allicin, often in garlic juice rather than the pure substance, was effective against human pathogens, including multi-drug resistant (MDR) strains and MRSE [9,22,36]
Summary
The antibacterial activity associated with garlic (Allium sativum L.) was identified by Cavallito in 1944 as being due to diallylthiosulfinate which was given the trivial name allicin [1,2]. In vivo allicin is formed by the catalytic action of alliin-lyase (E.C.4.4.1.4) on alliin (S-allyl-L-cysteine sulfoxide). Enzyme and substrate are compartmentalized separately in cells and become mixed after mechanical damage. Allicin is the first major sulfur-containing volatile to be produced and gives freshly crushed garlic its typical odor. Allicin has a broad spectrum of cellular targets and it is effective against bacteria, fungi, oomycetes, and protozoa [3,4,5,6,7,8]. Allicin’s mode of action is still not fully understood [9]
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