Agarose gel electrophoresis (1.2% agarose for 60-90 minutes) of amplified PCR products of blaSHV-12 gene (Genomic DNA) Lane L: 1500 bp DNA ladder Lanes 1-31: Amplified blaSHV-12 of phenotypic ESBL positive isolates SHV-1 found in the plasmid DNA of (21) 28% of the isolates. Figure (2) shows the results of PCR amplification of blaSHV-1 in plasmid DNA of the isolates. After running of PCR products inagarose gel, the isolates which gave positive result in PCR produced a band of 463 bp, which indicated the presence of blaSHV-11 gene. The blaSHV-11 has been described most often in K. pneumoniae(Nuesch-Inderbinenet al., 1997) and may be the ancestor of blaSHV2a and blaSHV-12 (Ford and Avison, 2004). The non-ESBL phenotype conferred by SHV11 shows that the Leu35Gln substitution between SHV-11 and SHV-1 has little or no significance with respect to hydrolysis of expanded-spectrum cephalosporins, therefore, its appearance is likely to be due to drift rather than antibiotic selection (Howard, et al. 2002).