INVESTIGATION OF THE MINIMUM INHIBITORY CONCENTRATION (MIC) AND MINIMUM BACTERICIDAL CONCENTRATION (MBC) OF THE AQUEOUS AND ETHANOLIC AVICENNIA MARINA EXTRACTS ON GRAM POSITIVE AND GRAM NEGATIVE BACTERIA “IN VITRO”

Background: Medicinal plants which are used for treating diseases have very few side effects compared to synthetic drugs. Avicennia marina plant extracts have been used for centuries as a popular method for treating several health disorders. The present study aimed to determine the antimicrobial effect of the aqueous and ethanolic extracts of Avicennia marina on Listeria monocytogenes PTCC 1297, Bacillus cereus PTCC 1154, Enterobacter aerogenes PTCC 1221, Enterococcus faecalis PTCC 1237, and Salmonella typhi PTCC 1609 “in vitro”. Methods: In this study, the antimicrobial effect of the extracts was evaluated by two methods, “Collins method” (spreading the extract on medium surface) and “disk agar diffusion method”. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) for both species were determined by using dilution method. Finally, the data were entered into the SPSS statistical software (version 18) and analyzed by t-test and Duncan’s test. Results: The results showed that in disk agar diffusion test, ethanolic extract had inhibition effects on Bacillus cereus and Enterococcus faecalis. MIC of Avicenna marina leaves of the aqueous and ethanolic extracts for Enterobacter aerogenes was 128 and 32 mg/ml, respectively. Besides, the MBC of aqueous and ethanolic extracts of Avicenna marina leaves for Enterobacter aerogenes was 256 and 64 mg/ml, respectively. Moreover, Enterobacter aerogenes was most resistant to the aqueous and ethanolic Avicenna marina extracts. Conclusions: The ethanolic extract of Avicenna marina leaves “in vitro” has a significant antimicrobial effect on Enterobacter aerogenes and Salmonella typhi (gram-negative bacteria) and Listeria monocytogenes, Bacillus cereus, and Enterococcus faecalis (gram-positive bacteria).