The infections risk related to pathogenic germs increases at the present time considering the increased resistance which certain microbes acquire, whose usual antibiotics are ineffective to treat the infectious disease. The aim of this study was to determine antimicrobial effect of the aqueous and ethanolic extracts of Lavandula stoechas L. and Rosmarinus officinalis L. on Listeria monocytogenes PTCC 1297 ،Bacillus cereus PTCC 1154، Enterobacter aerogenes PTCC 1221، Enterococcus faecalis PTCC 1237 and Salmonella typhi PTCC 1609 ”in vitro”. In this experimental study, after collecting plants from of Razavi Khorasan province, the extraction was carried out by the maceration method, after antimicrobial effect of the extracts evaluated by two methods, “Collins method” (spreading of the extract on medium surface) and “disk agar diffusion method”. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) for both species determined by using a dilution method. Statistical analysis was carried out by analysis of variance (ANOVA).The results show that aqueous and ethanolic Lavandula stoechas L. extracts were quite effective in 2000 μg/ml concentration on Listeria monocytogenes ،Bacillus cereus and Enterococcus faecalis. The results indicate that ethanolic extracts of Lavandula stoechas L. have the greatest effect on gram-positive bacterium. The result shows that MIC of Lavandula stoechas L. leaves of the aqueous and ethanolic extracts for Enterobacter aerogenes was 32 and 16 mg/ml respectively. The result shows that MIC of Rosmarinus officinalis L. leaves of the aqueous and ethanolic extracts for Enterobacter aerogenes was 128 and 64 mg/ml respectively.The Lavandula stoechas L. and Rosmarinus officinalis L. extracts presented the more effective impact on the growth of gram-positive bacteria than gram-negative bacteria (p<0.05).

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