Molecular characterization of the β-lactamases in Escherichia coli and Klebsiella pneumoniae from a tertiary care hospital in Riyadh, Saudi Arabia.

The widespread use of antimicrobials has increased the occurrence of multidrug resistant microbes. The commonest mechanism of antimicrobial resistance in Enterobacteriaceae is production of β-lactamases such as metallo-β-lactamases (MBL) and extended spectrum β-lactamases (ESBL). Few studies have used a molecular approach to characterize the prevalence of β-lactamases. Here, the prevalence of different β-lactamases was characterized by performing three multiplex PCRs targeting genes similar to those described in earlier publications. Antimicrobial susceptibility tests for all isolates were performed using the agar dilution method. β-lactamase was detected in 72% of the isolates, the detection rate being 64% in 2011 and 75% in 2012. The isolates were highly resistant to carbapenems such as meropenem and imipenem and susceptible to colistin and tigecycline. In this study, 22% of isolates contained both MBL and ESBL. ESBL was detected more frequently in Escherichia coli isolates, whereas carbapenemase was detected more frequently in Klebsiella pneumoniae isolates. These findings suggest the spread of multi-resistant ESBL and MBL producers in the community. Our results have implications for patient treatment and also indicate the need for increased surveillance and molecular characterization of isolates.