Detection of extended-spectrum β-lactamase (ESBL) and plasmid-borne blaCTX-M and blaTEM genes among clinical strains of Escherichia coli isolated from patients in the north of Iran.

Escherichia coli is an important cause of hospital-acquired infections worldwide. Antimicrobial resistance leads to treatment failure of hospital infections caused by E. coli. Production of extended-spectrum β-lactamases (ESBLs) is one of the major causes of antibiotic resistance in these bacteria. This study aimed to investigate the frequency of blaTEM and blaCTX-M genes in ESBL-producing E. coli strains isolated from clinical specimens of patients admitted to six hospitals in the north of Iran. A total of 160 E. coli strains were isolated from various clinical samples of hospitalised patients. Antibiotic resistance patterns were determined by the Kirby-Bauer disk diffusion method. The double-disk phenotypic confirmatory test was carried out amongst β-lactam-resistant isolates to detect ESBL-producing strains. Plasmid DNA of ESBL-producing strains was extracted and subjected to PCR for detection of the blaTEM and blaCTX-M genes, and isolates were extensively verified by sequencing. The highest resistance rate was to amoxicillin; all E. coli isolates (100%) were susceptible to imipenem. Amongst the 160 clinical E. coli isolates, 83 (51.9%) were ESBL-positive, of which 27 (32.5%) and 72 (86.7%) were positive for blaTEM and blaCTX-M, respectively. This study is the first report of an ESBL phenotype disseminated in hospitals in the north of Iran. These findings showed that there was a direct relationship between the development of resistance to β-lactam antibiotics and production of TEM and CTX-M enzymes.