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en Serotype Distribution and Multi Locus Sequence Type (MLST) of Erythromycin-Resistant Streptococcus Pneumoniae Isolates in Tehran, Iran زیست شناسی ملکولی Molecular Biology مقالات اصلی Original Article <div style="text-align: justify;">Background: The number of erythromycin-resistant Streptococcus pneumoniae has significantly increased around the world. The present study aimed to determine the serotype distribution and molecular epidemiology of the erythromycin-resistant Streptococcus pneumoniae (ERSP) isolated from patients with invasive disease. Methods: A total of 44 Streptococcus pneumoniae isolates were tested for susceptibility to several antimicrobial agents. Additionally, the polymerase chain reaction (PCR) was applied to evaluate ERSP isolates in terms of the presence of erythromycin resistance genes (e.g., ermB and mefA). The isolates were serotyped using the sequential multiplex-PCR method, and molecular epidemiology was assessed through the multilocus sequence typing (MLST) analysis. Results: The results represented multidrug resistance (MDR) in approximately half of the pneumococcal isolates. Among 22 ERSP isolates, 20 (90.9%) and 12 (56%) ones contained ermB and mefA, respectively. Further, 14 (31.8%), 3 (22.7%), and 19A (18.1%) were the common serotypes among the isolates. No significant correlation was observed between serotypes and erythromycin resistance genes. Furthermore, the MLST results revealed 18 different sequence types (STs), the top ones of which were ST3130 (3 isolates) and ST166 (3 isolates). Population genetic analysis disclosed that CC63 (32%), CC156 (18%), and CC320 (18%) were identified as the predominant clonal complexes. Conclusions: The ERSP isolates exhibited high genetic diversity. The large frequency of MDR isolates suggests the emergence of high resistant strains, as well as the need to implement vaccination in the immunization schedule of Iran. These accumulating evidences indicate that 13-valent pneumococcal conjugate vaccines provided higher serotype coverage in the ERSP isolates.  </div> Erythromycin Resistance, Genotyping Techniques, Multilocus Sequence Typing, Serotyping, Pneumococcal Vaccines. 259 268 http://rbmb.net/browse.php?a_code=A-10-431-2&slc_lang=en&sid=1 Mohammad Azarsa 100319475328460017936 100319475328460017936 No Department of Microbiology, Khoy University of Medical Sciences, Khoy, Iran. Mehrdad Mosadegh 100319475328460017937 100319475328460017937 No Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Soheila Habibi Ghahfarokhi 100319475328460017938 100319475328460017938 No Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Reza Pourmand mpourmand@tums.ac.ir 100319475328460017939 100319475328460017939 Yes Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.