Relationship between bla_SHV-12 and bla_SHV-2a in Korea

In contrast to the USA and Europe, where SHV-2, SHV-4 and SHV-5 are the prevalent extended-spectrum SHV enzymes, in Korea SHV-2a and SHV-12 are the most frequently identified extended-spectrum SHV enzymes. A 6.6 kb BamHI fragment containing the bla_SHV-12 gene of strain K7746 isolated from one university hospital in Korea was cloned into the pCRScript-CAM vector. Sequencing of the constructed recombinant plasmid pK7746-C1 revealed that the immediate upstream sequence of the bla_SHV-12 gene showed little similarity to the part of the prototype bla_SHV-1 gene due to the insertion of an IS26 element next to the -10 region. Instead, the upstream sequences of bla_SHV-12 retained 100% DNA identity with the part of plasmid pMPA2a from Klebsiella pneumoniae KPZU-3 carrying bla_SHV-2a. The restriction map of the inserted 6.6 kb DNA fragment of plasmid pK7746-C1 was also homologous to that of plasmid pMPA2a, suggesting a common lineage of bla_SHV-12 and bla_SHV-2a. We also studied, using PCR, the upstream non-coding region of several SHV β-lactamase genes for the presence of IS26 sequence. The flanking IS26 sequence in the immediate upstream region of the bla_SHV gene was not detected in five standard strains producing SHV-1, SHV-2, SHV-3, SHV-4 or SHV-5. However, IS26 was detected in all 69 clinical strains producing SHV-2a or SHV-12 isolated from three university hospitals in Korea during 1993-1999. The above findings suggest a direct evolution of SHV-12 from SHV-2a, not from SHV-2 to -5, and it is considered to be one of the reasons for the absolute predominance of SHV-2a and SHV-12 in Korea.