Mohammad Taha Ebrahimi - Department of Microbiology, School of Medicine, Tehran University of Medical Sciences
Mohsen Nazari - Department of Bacteriology, Pasteur Institute of Iran, Tehran, Iran
Niloofar Mobarezpour - PPD Tuberculin Department, Razi Vaccine & Serum Research Institute, Karaj, Iran
Hamed Afkhami - Department of Medical Microbiology, Faculty of Medicine, Shahed University of Medical Science, Tehran, Iran
Sepideh Fereshteh - Department of Bacteriology, Pasteur Institute of Iran, Tehran, Iran

Introduction: Heteroresistance is the phenomenon wherein subpopulations of microbes exhibit a range of resistance to an antibiotic and are prevalent in a broad range of microorganisms. Not much data on carbapenem and β-lactams heteroresistance among extra-intestinal pathogenic Escherichia coli (ExPEC) in blood infections is available. This study aimed to investigate the frequency of heteroresistance to β-lactams and carbapenems in ExPEC strains isolated from patients' blood in Tehran, Iran. Methods: Identification of E. coli isolates was performed using standard biochemical tests, and PFGE was employed to determine the E. coli isolates genotypes. Antibiotic resistance pattern to carbapenems (ertapenem, meropenem, and imipenem), cefotaxime, and cefepime was determined by measuring minimum inhibitory concentration (MIC). The results were used to assess β-lactam and carbapenem heteroresistance in E. coli isolates. Results: In this study, for the first time, heteroresistance to the antibiotics carbapenem (ertapenem, meropenem, and imipenem), cefotaxime, and cefepime was observed in E. coli isolates from blood samples. Sixteen samples had heteroresistance to antibiotics. Three and two isolates showed heteroresistance to imipenem and ertapenem, respectively. Simultaneous heteroresistance to two carbapenem family antibiotics in three isolates was detected. Also, three isolates showed heteroresistance to cefepime and five to cefotaxime. The imipenem-resistant isolates exhibited a higher level of heteroresistance than those resistant to other carbapenem antibiotics. Conclusions: The present study shows that heteroresistance is increasing in Iran. Furthermore, this study demonstrated increasing resistance to the carbapenem family.

Extraintestinal Pathogenic Escherichia coli, Heteroresistance, Broth microdilution, Agar dilution