Effect of garlic (Allium sativum L.) essential oil on growth of E. coli O157:H7 and shiga toxin 2 production

Increase of people’s awareness about side effects of chemical food preservatives has raised public interest to consume products with natural preservatives such as essential oils. Garlic (Allium Sativum L.) is one of the medicinal plants in traditional medicine of Iran and it is necessary to evaluate its antimicrobial effects on some food borne bacteria such as E.coli O157:H7. This bacteria has low infectious dose and causes hemorrhagic colitis and hemolytic-uremic syndrome.
The purpose of this study is to evaluate inhibitory effect of garlic essential oil (Allium Sativum L.) on growth of E. coli O157:H7 and shiga-toxin 2 (Stx2) production.
The minimum inhibitory concentration (MIC) of garlic essential oil was evaluated by broth microdilution method and minimum bactericidal concentration (MBC) methods. Effect of subinhibitory concentrations (subMICs) of garlic essential oil on bacterial growth over 72 h (at 35 °C) evaluated by surface plate counting and production of Stx2 were evaluated by kit (VTEC-RPLA).
MIC and MBC of garlic essential oil were estimated 0/02% and 0/04%, respectively. Concentrations of 0.005%, 0/01% and 0.015% of garlic essential oil reduced the bacterial growth. Concentration 0/015% after 72 h reduced 2 log10 (cfu/ml) growth rate and was the most effective concentration. Concentration 0/005% reduced Stx2 production and higher concentrations inhibited Stx2 production. It was found that the effect of different concentrations of essential oil on growth and production of Stx2 by E. coli O157:H7 were statistically significant (p≤0.05).
Garlic essential oil showed to be effective against bacterial growth and production of Stx2. This study indicated that garlic essential oil can be used as natural preservative in food system.