Abstract
Propyl-propane thiosulfinate (PTS) and propyl-propane thiosulfonate (PTSO) are two volatile compounds derived from Allium cepa with a widely documented antimicrobial activity. The aim of this study was to evaluate their anti-candidiasis activity and the ability of its gaseous phase to inhibit bacterial and yeast growth in vitro. The minimum inhibitory concentration of various antifungal products (including PTS and PTSO) was determined versus 203 clinical isolates of Candida spp. through broth microdilution assay. Additionally, the antimicrobial activity through aerial diffusion of PTS and PTSO was evaluated over the growth of a collection of bacteria and yeasts cultivated in agar plates. All yeasts were susceptible to the antifungals tested, except C. glabrata and C. krusei, that showed azole resistance. PTSO (MIC50 and MIC90 ranged from 4 to 16 mg/L and 8 to 32 mg/L, respectively) was significantly more active against yeasts than PTS (MIC50 and MIC90 ranged from 16 to 64 mg/L and 32 to 64 mg/L). Values were higher than those obtained for antifungal drugs. Gaseous phases of PTS and PTSO generated growth inhibition zones whose diameters were directly related to the substances concentration and inversely related to the microbial inoculum. The quantification of PTS and PTSO levels reached in the growth media through aerial diffusion displayed a concentration gradient from the central zone to the periphery. Only P. aeruginosa ATCC 27853 showed resistance, while yeasts (C. albicans ATCC 200955 and C. krusei ATCC 6258) presented the higher susceptibility to both compounds. These results suggest that PTS and PTSO display antibacterial and anti-candidiasis activity in vitro through aerial diffusion, having potential use in human therapy.
Highlights
The antioxidative, hypolipidemic, hypocholesterolemia, antihypertensive, heart-protective, antithrombotic, anticancer, anti-inflammatory, immunomodulatory, and antimicrobial activities of different organosulfur products, such as thiosulfinates and thiosulfonates obtained from garlic (Allium sativum) and onion (Allium cepa), especially allicin, have been thoroughly studied [1,2,3]
They can react with thiols, such as glutathione, increasing the oxidized glutathione rate into a range that induces oxidative stress and cellular apoptosis [7]; they can interact with enzymes taking part of the microbial system of acetyl-CoA blocking the incorporation of acetate into fatty acids and inhibiting the development of a phospholipid bilayer of the membranes [5]; and they can inhibit RNA polymerase and, block the total synthesis of microbial RNA [8]
The aim of this study was to evaluate anti-candidiasis activity of propane thiosulfinate (PTS) and propane thiosulfonate (PTSO) in vitro and the capacity of its gaseous phase to inhibit the growth of different bacteria and yeasts
Summary
While the precise mechanism of action has not yet been discovered, the main antimicrobial effect of these Allium-derived compounds has been reported to be due to its chemical reaction with thiol groups present in the main enzymes of the microbial metabolism, such as succinate dehydrogenase, alcohol dehydrogenase, thioredoxin reductase and ureases among others, via thiol-disulfide exchange reaction [4,5,6]. It is more stable than allicin, PTS is a labile compound that, through dismutation or disproportionation reactions, changes into dipropyl disulfide and propyl-propane thiosulfonate (PTSO) [10]
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