Prevalence and characteristics of ST131-O16 and ST131-O25b clones among extended-spectrum β-lactamase-producing Escherichia coli isolates causing bloodstream infection in Iran.

Background: The multidrug-resistant clone identified as Escherichia coli sequence type 131 (E. coli ST131) has spread worldwide. The current study is one of the first comprehensive investigations to ascertain the prevalence of ST131 and molecularly characterize the ST131-O25b and ST131-O16 subgroups causing bloodstream infections in Iran.

Methods and results: To this end, 119 consecutive, non-repetitive E. coli clinical strains were isolated from blood samples of patients with septicemia in different hospital wards for one year in Tehran. The isolates were provided by the laboratories of tertiary hospitals affiliated with Tehran University of Medical Sciences. The disk diffusion method was used to investigate the sensitivity of bacteria to antibiotics. All phylogroup B2 isolates were screened for E. coli ST131 status using a triplex PCR assay that combines the identification of ST131-O25b and -O16 clades. The seven putative virulence factor genes (kpmstII, fimH, afa A, iroN, Sat, ibeA, and ompT) and resistance genes (bla_CTX-M-15, bla_OXA-48, and bla_CMY) were detected by PCR in E. coli ST131 isolates.

Conclusions: The highest incidence of antibiotic resistance among 74/119 (62.18%) extended-spectrum β-lactamases-producing E. coli isolates was observed, respectively, against Nalidixic acid (82%), and Aztreonam (75%), followed by Ciprofloxacin (70%). Twenty out of 74 ESBL-producing E. coli isolates were found to be ST131 (27%), with 13 (65%) ST131-O25b and 7 (35%) ST131-O16 clades, respectively. The ST131-O16 isolates had a higher prevalence of resistance to Ceftriaxone, Amikacin, Aztreonam, and Cefepime than the -O25b ones. Concerning virulence capacity, our findings demonstrated that kpmstII, fimH, and ompT genes were found in 85%, 65%, and 30% of ST131 isolates, respectively. Our results reinforce the surveillance of E. coli ST131 clone dissemination as a major drug-resistant pathogen and an important new public health threat in Iran. Accumulation of multiple virulence factors, ESBL carriage, and identified antimicrobial resistance patterns of ST131-O25b and ST131-O16 clones indicate a necessity to develop strategies to control the spread of these isolates in both community and hospital settings.