en Anti-microbial agents, resistance and treatment protocols Anti-microbial agents, resistance and treatment protocols Original article Original article <strong>Introduction: </strong>Dental caries is a significant public health problem which destroys the calcified tissues of the teeth. The frequency of<em> lactobacilli </em>in dental caries is usually high. The objective of this study was to evaluate the incidence of these bacteria in dental caries and to identify the antibiotic resistance patterns of them. <strong>Methods: </strong>Specimens from dental plaque were collected from 30 patients. Phenotypic (Gram staining, cell morphology, and biochemical tests) and molecular (PCR) methods were used for identification of <em>Lactobacillus</em> bacteria. The antimicrobial sensitivity test was performed by standard Kirby-Bauer disk diffusion method to determine their resistance to chloramphenicol, penicillin, vancomycin, nitrofurantoin, cefixime, cefazolin, amoxicillin-clavulanic acid, and tetracycline. Antibiotic resistance genes were detected using multiplex PCR method as well. <strong>Results: </strong>Fourteen out of 30 (46/6%) samples were <em>Lactobacillus</em> positive. The <em>mecA</em> was the essential gene responsible for penicillin resistance. Also, the <em>bla_TEM</em> and bla<em>_OXA-</em>₁genes had more significant role in cefazolin and cefixime resistance than <em>bla_SHV</em>, and <em>these </em>two genes had the similar role in the amoxicillin-clavulanic acid resistance. Also, tetracycline resistance was caused by both <em>tetK</em> and <em>tetM</em> genes identically. <strong>Conclusion: </strong>In conclusion, <em>Lactobacillus </em>bacteria had an essential role in the formation of dental plaque and showed multidrug-resistant patterns to commonly used antibiotics. Dental plaque, Lactobacillus, Multiplex PCR, resistance genes 51 55 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-116-2&slc_lang=en&sid=1 Sahar Nouri Gharajalar saharnouri@yahoo.com Yes Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran Masoumeh Firouzamandi No Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran