 Resistance to broad-spectrum cephalosporins through the acquisition and expression of Extended-Spectrum β-lactamase ESBL among Enterobacteriacea is increasing. The clinical implications of ESBLs are extremely serious and sensitive diagnostic methods are urgently needed to guide therapy, monitor resistance development and implement intervention strategies. Conventionally, detection of expression of ESBLs was based on reduction of ceftazidime of cefotaxime MICs by 3 two fold dilutions in the presence of clavulanic acid. However, the use of the above method was limited to cover only some of the bacterial species, including predominantly E. coli and Klebsiella spp., or tested strains which were all transconjugants generated in vitro. ESBLs are now reported in a growing number of genera other than E. coli or Klebsiella spp., and Serratia marcescens. 