Abstract
To demonstrate different effects of garlic extracts and their main antibiotic substance allicin, as a template for investigations on the antibacterial activity of food ingredients. Staphylococcus epidermidis ATCC 12228 and the isogenic biofilm-forming strain ATCC 35984 were used to compare the activity of allicin against planktonic bacteria and bacterial biofilms. The minimal inhibitory concentration (MIC) and the minimum biofilm inhibitory concentration (MBIC) for pure allicin were identical and reached at a concentration of 12.5 μg/mL. MBICs for standardized garlic extracts were significantly lower, with 1.56 and 0.78 μg/mL allicin for garlic water and ethanol extract, respectively. Biofilm density was impaired significantly at a concentration of 0.78 μg/mL allicin. Viability staining followed by confocal laser scanning microscopy showed, however, a 100% bactericidal effect on biofilm-embedded bacteria at a concentration of 3.13 μg/mL allicin. qRT-PCR analysis provided no convincing evidence for specific effects of allicin on biofilm-associated genes. Extracts of fresh garlic are more potent inhibitors of Staphylococcus epidermidis biofilms than pure allicin, but allicin exerts a unique bactericidal effect on biofilm-embedded bacteria. The current experimental protocol has proven to be a valid approach to characterize the antimicrobial activity of traditional food ingredients.
Highlights
Garlic (Allium sativum) is recognized as a medicinal herb for more than 5000 years and truly deserves to be described as functional food
The antimicrobial activity of garlic extract, the water-soluble ingredients such as allicin, have gained recently increasing attention as they are active against emerging pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) (Cutler and Wilson 2004) and plaque-forming organisms in the oral cavity, which may be associated with garlic consumption (Bachrach et al 2011)
Ria treated with gWE containing 1.56 lg/mL allicin, rendered ~70% and 60% of nonviable bacteria, and a 100% loss of viability was observed at a concentration of 3.13 lg/mL of allicin in the extract (Fig. 4A3 and B3)
Summary
Garlic (Allium sativum) is recognized as a medicinal herb for more than 5000 years and truly deserves to be described as functional food. Due to its antioxidant capacity garlic prevents rancidity and exerts antimicrobial activity prolonging the shelf life of meat products and increasing food safety due to its effect against zoonotic pathogens such as Staphylococci, Salmonella spp., and Escherichia coli (Ankri and Mirelman 1999). The antimicrobial activity of garlic extract, the water-soluble ingredients such as allicin, have gained recently increasing attention as they are active against emerging pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) (Cutler and Wilson 2004) and plaque-forming organisms in the oral cavity, which may be associated with garlic consumption (Bachrach et al 2011).
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