Detection of extended spectrum beta-lactamases in Escherichia coli and Klebsiella pneumoniae.

The presence of extended spectrum beta-lactamases (ESbetaLs) in 129 Escherichia coli and 128 Klebsiella pneumoniae strains was determined with the E test. beta-lactamases were detected in 66 (51.2%) of E.coli and 107 (83.6%) of K. pneumoniae by the nitrocefin disk method. Putative ESbetaL production was observed in 15.5% of E. coli and 55.5% of K. pneumoniae with the E test. Among the putative ESbetaL-producer strains 11 were found to be susceptible to ceftizoxime, 6 to ceftazidime, 2 to ceftriaxone, cefotaxime and aztreonam, and one to cefoperazone according to the disk diffusion test. All putative ESbetaL-producers were resistant to cefodizime, thus it may be a good indicator of the presence of mainly TEM-type ESbetaL. The E test was also found to be practicable for the detection of ESbetaLs in clinical laboratory. Further studies are needed to clarify whether ESbetaL can be identified reliably in species that, in addition to plasmid mediated ESbetaL production, chromosomally encoded AmpC beta-lactamases and other class A ESbetaLs by disk diffusion test.