Phylogenetic Diversity of Extended Spectrum beta-lactamase Producing Escherichia coli in Fecal Isolates of Healthy People in Tehran

Background and Objectives: Association of fecal Escherichia coli (E. coli) phylogroups with human diseases and role of these strains in dissemination of resistance genes are one of major health concerns. In new Clermont phylogenetic group, isolates of E.coli were divided into seven phylogroups termed A, B1, B2, C, D, E and F. Studies have shown that these phylogroups differ in the presence of virulence factors, ecological niches and life history. Strains from phylogroups B2 and D have more virulence factors than those from the phylogroups A and B1. The aim of this study was to investigate the phylogroups diversity among fecal E. coli, isolated from healthy young people in Tehran.Materials and Methods: A total of 233 ESBL- positive E.coli isolated from fecal samples of healthy young people in 2018 in Tehran, were included in this study. Antimicrobial susceptibility test for 13 antibiotics from different classes according to the last CLSI guideline was performed using Kirby-Bauer disk diffusion test. Then, the presence of an ESBL was confirmed by a phenotypic confirmatory disk diffusion test using ceftazidime and ceftazidime-clavulanic acid disks. The blaCTX-M gene also was detected by PCR. Diversity of phylogroups A, B1, B2, C, D, E and F was analyzed among ESBLs positive isolates by PCR. Results: The blaCTX-M gene was detected in 91.8% of ESBL positive isolates. In this study, frequencies of phylogroups were as follows: A =117(49.8%), D =57(24.3%), B2 =30 (12.8%), B1= 9 (3.8%), C and F each equal to 7 (3%) and E =1 (0.4%). High level resistance was observed for ampicillin (98.3%), trimethoprim/sulfomethoxazole (80.4%) and nalidixic acid (67.2%), mostly belonged to phylogroup D. Conclusion: Contrary to another study which showed A and B1 phylogroups are dominant in commensal isolates, in our study a high percent of commensal fecal E.coli isolates was clustered in phylogroup A, followed by group D with high antibiotic resistance pattern. Geography, climate, diet, gut morphology, body mass, sex, age, hygiene level may be associated with the distribution of phylogroups. The colonization of the intestine with E. coli strains related to phylogroups D, as a source of extra intestinal pathogenic E. coli strains responsible for human diseases, and carriage of -lactamase genes in these strains proposed them as a source of pathogenic strains in human.