Variations in the prevalence of strains expressing an extended-spectrum beta-lactamase phenotype and characterization of isolates from Europe, the Americas and the Western Pacific region

To evaluate the prevalence of extended-spectrum beta -lactamase (ESBL)-prod ucing strains among species of Enterobacteriaceae, a microdilution suscepti bility test was performed with strains of Klebsiella pneumoniae, Escherichi a coli, Proteus mirabilis, and Salmonella species that were isolated as par t of the SENTRY project. The highest percentage of ESBL phenotype (defined as a minimum inhibitory concentration [MIC] greater than or equal to2 mug/m L for ceftazidime, ceftriaxone, or aztreonam) was detected among K. pneumon iae strains from Latin America (45%), followed by those from the Western Pa cific region (25%), Europe (23%), the United States (8%), and Canada (5%). P. mirabilis and E. coli strains for which MICs of extended-spectrum cephal osporins or monobactams were elevated also were more prominent in Latin Ame rica. Testing with ceftazidime revealed more isolates with elevated MICs th an did testing with ceftriaxone or aztreonam. ESBL strains showed high leve ls of co-resistance to aminoglycosides, tetracycline, trimethoprim-sulfamet hoxazole, and ciprofloxacin. Imipenem remains highly effective against ESBL strains. Organisms expressing an ESBL are widely distributed worldwide, al though prevalence rates are significantly higher in certain geographic regi ons.