Comparison of the sensitivity for detection of extended spectrum beta lactamase by three methods

Objective To compare the sensitivity of three methods for the detection of extended spectrum beta lactamases(ESBLs) produced by E. coli and K. pneumoniae.Methods Fourteen strains of E. coli and 6 strains of K. pneumoniae suspiciously produced ESBLs detected by a disc diffusion screen test among 73 E. coli and K.pneumoniae clinical isolates. A disc diffusion confirmatory test, Etest, and a double disc synergy test detected these 20 strains.Results All of the 20 strains were ESBLs producing strains by cefotaxime and cefotaxime clavulanic acid of the disc diffusion confirmatory test, but there were 12 ESBLs positive strains among 13 suspicious ESBLs producing strains tested by ceftazidime and ceftazidime clavulanic acid. Among the 20 strains, 12 ESBLs producing strains were detected by Etest with ceftazidime and ceftazidime clavulanic acid. All of the 20 strains were ESBLs positive by double disc synergy test with cefotaxime, but only 14 were the ESBLs positive with ceftazidime.Conclusion Among the three methods, the sensitivity of cefotaxime was higher than that of ceftazidime.