Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 10 4 2018 10 06 254 257 EN Leila Rahimvand Faculty of Dentistry, Shahed University, Tehran, Iran Mohammad Niakan Department of Microbiology, Faculty of Medicine, Shahed University, Tehran, Iran Noushin Jalayer Naderi Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, Shahed University, Tehran, Iran 2017 10 27 2018 08 02 Background and Objectives: Anaerobic Gram negative bacteria are the main cause of periodontal destruction. It has been shown that Myrtus communis have anti-bacterial activity on Gram positive and Gram negative bacteria. The aim of this study was to determine the antibacterial effect of aquatic and methanolic extract of Myrtus communis on some of the oral Gram-negative bacteria. Materials and Methods: The antibacterial effect of aquatic and methanolic extracts of Myrtus communis was determined using disk diffusion method at different concentrations from 10 to 500 mg/ml. The diameter of inhibition zones were determined. The MIC was defined using the standard broth macrodilution method. The results of the study were reported descriptively. Results: The aquatic extract of Myrtus communis from 20 to 500 mg/ml had antibacterial effect on Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis and Prevotella intermedia. The methanolic extract from 10 to 500 mg/ml had antibacterial effect on A. actinomycetemcomitans, P. gingivalis and P. intermediate. The MIC was achieved at 10 mg/ml, 10 mg/ml and 10 mg/ml for aquatic and methanolic extracts of Myrtus communis on A. Actinomycetemcomitans, P. Gingivalis and P. Intermediate, respectively. Conclusion: Aquatic and methanolic extracts of Myrtus communis had antibacterial effect on P. gingivalis, A. actinomycetemcomitans and P. intermediate. Most concentrations of aqueous extract were effective on bacteria, so, providing an alcoholic extract, that is a time consuming and costly method, does not seem necessary. https://ijm.tums.ac.ir/index.php/ijm/article/view/1529 https://ijm.tums.ac.ir/index.php/ijm/article/download/1529/1063