Short Communication High prevalence of sequence type 131 isolates producing CTX-M-15 among extended-spectrum β-lactamase-producing Escherichia coli strains in northeast Iran Marzie Moghanni a , Kiarash Ghazvini a , Hadi Farsiani a , Mohammad Hasan Namaei b , Mohammad Derakhshan a , Masoud Yousefi a , Alimohammad Maragheh c , Saeid Amel Jamehdar a, * a Antimicrobial Resistance Research Center, Mashhad University of Medical Sciences, Azadi Square, Medical Campus, Mashhad 9177948564, Iran b Infectious Diseases Research Centre, Birjand University of Medical Sciences, Birjand, Iran c Medical Laboratory Basic Sciences, 17 Shahrivar Hospital, Iranian Social Security Organization, Mashhad, Iran A R T I C L E I N F O Article history: Received 22 August 2017 Received in revised form 8 May 2018 Accepted 19 May 2018 Available online 25 May 2018 Keywords: Escherichia coli Sequence type 131 ST131 ESBL CTX-M-15 Iran A B S T R A C T Objectives: The recent expansion of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is a worldwide problem. The purpose of this study was to investigate the molecular characteristics of ESBL- producing E. coli strains in Mashhad, located in the northeast of Iran. Methods: A total of 455 clinical E. coli isolates were collected at three hospitals in Mashhad between April–September 2015. Antimicrobial susceptibility was determined by the Kirby–Bauer disk diffusion test. The combination disk test was performed for phenotypic detection of ESBLs. PCR was used to screen isolates for ESBL typing. Phylogenetic groups and sequence type 131 (ST131) were determined by multiplex PCR. Results: The prevalence of ESBL-producing E. coli among the collected strains was 51.6% (235/455). Among the 235 ESBL-producing strains, 222 (94.5%) tested positive for CTX-M type, whilst 115 (48.9%), 92 (39.1%) and 21 (8.9%) were positive for TEM, OXA and SHV, respectively. Moreover, CTX-M-15 (94.1%; 209/222) was the most common ESBL among E. coli. Based on multiplex PCR, phylogenetic group B2 was predominant (169/235; 71.9%), followed by D (32/235; 13.6%), A (21/235; 8.9%) and B1 (13/235; 5.5%). ST131 was the predominant clonal group among the phylogenetic group B2 isolates (151/169; 89.3%). Conclusion: The results revealed that an urgent investigation of the source and transmission pathways of the CTX-M-15-B2-ST131 E. coli clone is needed to mitigate this emergent public-health problem. © 2018 International Society for Chemotherapy of Infection and Cancer. Published by Elsevier Ltd. All rights reserved. 1. Introduction Escherichia coli is a normal gut bacterium, but at the same time it is an important opportunistic pathogen causing infections in hospitals and serves as a common cause of urinary tract infections (UTI), bacteraemia, meningitis and gastrointestinal tract infections in humans. Antimicrobial agents used to treat E. coli infections include β-lactams, fluoroquinolones and aminoglycosides [1]. However, in recent years infections caused by extended-spectrum β-lactamase (ESBL)-producing E. coli have been observed worldwide. The majority of ESBLs can be divided into nine distinct families, including TEM, SHV, CTX-M, PER, VEB, GES, BES, TLA and OXA. Until the late 1990s, TEM and SHV were the predominant ESBL types. However, over the past decade, CTX-M enzymes have emerged around the world and have become the most prevalent ESBLs in E. coli strains [2]. Unlike TEM and SHV, the CTX-M enzymes have been observed in nosocomial and community settings. CTX-M enzymes are characterised by their ability to confer resistance to cefotaxime but not ceftazidime. A notable exception to this is CTX-M-15, the most common CTX-M variant, which can also confer resistance to ceftazidime in addition to cefotaxime. CTX-M-15 is now the predominant CTX-M genotype in many parts of the world [3]. ESBL-producing E. coli have recently been reported to have acquired emerging resistance determinants, * Corresponding author. E-mail address: ameljs@mums.ac.ir (S.A. Jamehdar). https://doi.org/10.1016/j.jgar.2018.05.016 2213-7165/© 2018 International Society for Chemotherapy of Infection and Cancer. Published by Elsevier Ltd. All rights reserved. Journal of Global Antimicrobial Resistance 15 (2018) 74–78 Contents lists available at ScienceDirect Journal of Global Antimicrobial Resistance journal home page : www.e lsevier.com/loca te/jgar