Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 8 1-2 2019 02 19 51 57 EN Fataneh Moein Jahromi Department of Microbiology, Islamic Azad University, Jahrom Branch, Jahrom, Iran. Mohammad Kargar Department of Microbiology, Islamic Azad University, Jahrom Branch, Jahrom, Iran Abbas Doosti Biotechnology Research Center, Islamic Azad University, Shahrekord Branch, Shahrekord, Iran Somayeh Handali Nanotechnology Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. 2016 06 04 2016 06 13 Background: Streptococcus pneumoniae is an important cause of respiratory tract infections.  Due to the recent incidence of antibiotic resistance to commonly used antibiotics, the use of quinolones in the treatment of S. pneumoniae has been taken into consideration. The aim of this study was to evaluate the molecular mechanisms of quinolone resistance in isolated strains. Methods:This study was carried out on 45 strains of S. pneumoniae isolates from clinical samples. Initially, using biochemical tests, S. pneumoniae strains were determined and using lytA gene specific primers, these strains were accomplished. Antibiotic resistance was assessed by Clinical & Laboratory Standards Institute (CLSI) criteria and eventually, and then adopting Polymerase Chain Reaction- Restriction Fragment Length polymorphism (PCR-RFLP) techniques were studied with Sau3A andMspI enzymes. Also, point mutations associated with antibiotic resistance was evaluated in parC and parE genes. Results: In 45 strains isolated, resistance to nalidixic acid, ciprofloxacin, ofloxacin, norfloxacin and levofloxacin was; 82.22%, 73.43%, 53.33%, 48.88%, and 42.22%, respectively. In clinical samples,34 (75.55%) strains with mutations in the parC genes and 14 (31.11%) strains with mutations in parE gene were detected. Using statistical analysis, it was found that there was a significant relationship between mutations in the parC genes and resistance to nalidixic acid, ciprofloxacin, norfloxacin and levofloxacin.  However,  mutations  in  parE  genes  only  showed  the  significant  correlation  with resistance to norfloxacin exclusively. On the contrary, unlike other studies, we demonstrated that a mutation in the parE gene could be involved in low-level resistance to quinolones. Conclusion: Due to the considerable resistance to quinolones, evaluation of these mutations isnecessary in other parts of the country.   https://jmb.tums.ac.ir/index.php/jmb/article/view/144 https://jmb.tums.ac.ir/index.php/jmb/article/download/144/283