Evaluation of antibacterial activity of ethanol extracts of some medicinal plants against Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen capable of causing outbreak or sporadic episodes in human. Most of the outbreak or sporadic episodes were in the last two decades and due to high rate of mortality, caused a great concern in food industries. There are various medicinal plants with the high performance of antibacterial activity in Iran. The present study investigated the anti-listerial activity of some of these palnts against two serotypes of foodborne L. monocytogenes. The plants were used included: Thymus vulgaris L., Eucalyptus globulus Labill. Matricaria recutita L, Rosmarinus officinalis L and Saliva officinalis L. The plants were selected and identified by Pharmacognosy Department of Isfahan Faculty of Pharmacy. Extracts of the selected plants were prepared. Then antibacterial activity of these extracts was determined by disc diffusion method. The Minimal Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were also determined by the serial dilution method. Ampicillin (10 µg/disc) used in the test as standard. Only ethanolic extract of Eucalyptus showed antibacterial effects against L. monocytogenes in both disc diffusion and serial dilution method. MIC and MBC of this extract were 31. 25 µg/ml and 500 µg/ml, respectively. There was no significant difference between the sensitivity of the two serotypes. Extract of other plants did not show any antibacterial effects against L. monocytogenes. Based on our results, only the extract of Eucalyptus showed antibacterial effects on both serotypes. Using other extraction methods and higher concentration of extracts may cause stronger antibacterial effect on L. monocytogenes.