Phenotypic and genotypic characterization of extended-spectrum β-lactamases producing Escherichia coli and Klebsiella pneumoniae in a tertiary care hospital in Riyadh, Saudi Arabia

BACKGROUND AND OBJECTIVES: Extended-spectrum beta-lactamase (ESBL)-producing pathogens remain a public health concern, with limited data on the molecular characterization of isolates. We aimed to determine the molecular characterization of ESBL-producers circulating in our setting and correlate the molecular types with the minimal inhibitory concentration (MIC) to third-generation cephalosporins. DESIGN AND SETTING: Retrospective study conducted during the period from January to June 2013 at King Khalid University hospital, a tertiary-care hospital in Riyadh, Saudi Arabia. MATERIALS AND METHODS: All Escherichia coli and Klebsiella pneumoniae confirmed to be ESBL producers were included. The MICs of ceftriaxone and ceftazidime were determined by the E-test. Molecular characterization of ESBL-genes was performed using the Check-MDR-CT102 DNA microarray. RESULT: Of 77 isolates comprising 50 (65%) E coli and 27 (35%) K pneumoniae, the majority (n=63; 81%) were from urine. Most isolates were bla(CTX-M) gene positive (n=72/77; 93.5%) comprising bla(CTX-M1) (n=62), bla(CTX-M9) (n=9) and bla(CTX-M25) (n=1). Two or more ESBL genes were present in 45% of isolates with bla(SHV) predominating in K pneumoniae and bla(TEM) in E coli. Two isolates were positive for blaOXA-48 carried in combination with bla(CTX-M9) and bla(TEM) in E coli and bla(CTX-M1)/(CTX-M9) in K pneumoniae. Ceftriaxone MIC50 and MIC90 of ≥256 μg/mL were seen in E coli and K pneumoniae harboring bla(CTX-M) alone or in combination with bla(SHV) or bla(TEM). For ceftazidime the highest MIC50 and MIC90 was seen in K pneumoniae harboring bla(CTX-M)+bla(SHV) and E coli with bla(CTX-M)+bla(TEM) combinations. CONCLUSION: A preponderance of bla(CTX-M) suggests dissemination of the gene in our setting. The MIC for ceftriaxone and ceftazidime correlate well with molecular characterization of ESBL-producing Enterobacteriaceae.