en Anti-microbial agents, resistance and treatment protocols Anti-microbial agents, resistance and treatment protocols Original article Original article <span style="font-size:11pt"><span style="line-height:normal"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">Introduction: </span></span></b><span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">Mutans Streptococci are significant pathogens isolated from dental plaques. Due to the increasing frequency of antimicrobial resistance among pathogens causing dental caries, more studies have focused on using natural agents against them. This study aimed to evaluate the antibacterial effects of <i>Trachyspermum ammi</i></span></span><b><i> </i></b><span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">essential oil against <i>Streptococcus mutans </i>isolated from dental plaques. <b>Methods:</b> Twenty human dental plaque samples were collected, and eight <i>S. mutans</i> isolates were detected using biochemical and molecular tests. The antibiotic susceptibility patterns of the isolates were determined <span style="background:white">by the disc diffusion method</span>. Also, <i>T. ammi</i> essential oil antibacterial activity was investigated using the disc diffusion method and determining minimum inhibitory concentration (MIC50) and minimum bactericidal concentration (MBC) values. <b>Results:</b><i> </i>Phenotypic and genotypic characterization identified <i>S. mutans</i> in 40% of the samples. The antibiotic susceptibility assay revealed the highest resistance patterns against cefotaxime (100%), ceftriaxone (100%), and penicillin (87.5%). The <i>T. ammi </i>essential oil demonstrated 20</span></span> <span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">&micro;g/ml MIC and 80&micro;g/ml MBC against</span></span> <i><span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">S. mutans</span></span></i><span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">. <b>Conclusion:</b> The present study revealed a potent antibacterial activity for <i>T. ammi </i>essential oil against <i>S. mutans </i>isolates.&nbsp; </span></span></span></span></span><br> &nbsp; Dental plaque, Streptococcus mutans, Trachyspermum ammi, Essential oil 192 198 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-116-4&slc_lang=en&sid=1 Sahar Nouri Gharajalar saharnouri@yahoo.com 0000-0002-5123-5227 Yes Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran. Mohsen Hassanzadeh moh3enemail@yahoo.com No DVM student, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran. Razzagh Mahmoudi r.mahmodi@yahoo.com 0000-0002-6280-0404 No Medical Microbiology Research Center, Qazvin University of Medical sciences, Qazvin, Iran Paria Emamverdizadeh emamiparya@yahoo.com 0000-0002-4406-9558 No Oral and Maxillofacial Pathology Department, Dentistry Faculty, Tabriz University of Medical Sciences, Tabriz, Iran