Prevalence of Extended-Spectrum Beta-Lactamases in Enterobacteriaceae, Pseudomonas and Stenotrophomonas as Determined by the VITEK 2 and E Test Systems in a Kuwait Teaching Hospital

Objective: To determine the prevalence of extended-spectrum β-lactamase (ESBL)-producing members of the Enterobacteriaceae using VITEK 2 and E test systems. Materials and Methods: A total of 3,592 consecutive gram-negative isolates (single isolate per patient) of the family of Enterobacteriaceae and Pseudomonas adjudged to be clinically relevant to the patient’s infection were studied for ESBL production over a period of 1 year at Mubarak Al-Kabeer Hospital, Kuwait. Two methods were used: the automated VITEK 2 system and E test ESBL, a manually manipulated plastic strip containing various gradients of β-lactam antibiotics. These tests and interpretative criteria for the results were performed according to the manufacturer’s instructions. Results: Of the 3,592 bacterial isolates, 264 (7.5%) and 185 (5.2%) were positive for ESBL production by the VITEK 2 and E test, respectively. All the ESBL-producing Pseudomonas aeruginosa identified by VITEK 2 gave indeterminate results by E test. Prevalent ESBL producers, identified by the VITEK 2 versus E test, respectively, were: Citrobacter spp. (15 vs. 3.2%), K. pneumoniae (12.2 vs. 11.4%), Enterobacter spp. (12 vs. 3%), E. coli (6.5 vs. 5.6%), P. aeruginosa (6.5 vs. 0%) and Morganella spp. (2 vs. 1%). The most common infection associated with ESBL-producing pathogens was urinary tract infection (68.2%), followed by wound infection (14.4%) and bloodstream infection (6.1%). Conclusion: The result of this study showed a relatively high prevalence of clinically significant ESBL producers among the Enterobacteriaceae and Pseudomonas spp. at our teaching hospital. The VITEK 2 identified a higher prevalence of ESBL strains than the E test.