Phenotypic and genotypic identification of extended spectrum β-lactamases (ESBLs) among clinical isolates of Escherichia coli

Extended spectrum β-lactamases (ESBLs) are emerging, diverse group of plasmid - associated antibiotic resistant enzymes that are presenting a public health concern. ESBLs were detected in Escherichia coli by performing phenotypic tests on 18 out of 35 E. coli isolates recovered from urine samples of patients with urinary tract infections in three Eygpt hospitals and identified as positive ESBLs according to CLSI screening criteria. Results of phenotypic confirmatory tests revealed that, broth microdilution test, combination disc test and double disc synergy test confirmed 14(78%), 16(89%) and 16(89 %), respectively of E. coli isolates as positive ESBLs. Genotypic screening using PCR was performed by testing for blaCTX-M, blaTEM and blaSHV enzymes. Sixteen phenotypic ESBL isolates were positive for β-lactamase genes. Ten isolates produced both blaCTX-M and blaTEM, and 6 isolates produced blaCTX-M only, while blaSHV was not detected in any isolate. The sensitivity and specificity of combination disc and broth microdilution tests compared to PCR were 100%, while double disc synergy test showed sensitivity and specificity of 87.5 and 100% respectively. ESBL isolates were found to have multi-drug resistance pattern. No correlation could be made between type of ESBL and antimicrobial susceptibility profile of the isolate. Key words: Extended spectrum β-lactamase, bla (TEM), bla (CTX-M), urinary tract infection