High prevalence of sequence type 131 isolates producing CTX-M-15 among extended-spectrum β-lactamase-producing Escherichia coli strains in northeast Iran.

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.