Detection of extended-spectrum beta-lactamases in klebsiellae with the Oxoid combination disk method.

The Oxoid combination disk method for detecting extended-spectrum beta-lactamases (ESBLs) depends on comparing the inhibition zones of cefpodoxime (10-microg) and cefpodoxime-plus-clavulanate (10- plus 1-microg) disks. The presence of clavulanate enlarged the zones for all of 180 ESBL-producing klebsiellae by >/=5 mm, whereas zones for cefpodoxime-susceptible isolates and cefpodoxime-resistant isolates with AmpC and K1 beta-lactamases were enlarged by </=1 mm. Good discrimination was achieved with either the NCCLS or the British disk method.