Close evolutionary relationship between the chromosomally encoded β lactamase gene of Klebsiella pneumoniae and the TEM β‐lactamase gene mediated by R plasmids

Sixty‐three percent homology of nucleotide sequence and 67% homology of deduced amino acid sequence were found between the chromosomally encoded β‐lactamase gene of Klebsiella pneumoniae and the TEM β‐lactamase of transposon Tn3. Moreover, 22 out of 24 amino acid residues are identical around the predicted active site. It is therefore suggested that these two kinds β‐lactamases share a common evolutionary origin. The 0.5 kb DNA fragment of the cloned gene hybridized specifically with the chromosomal DNA of all the K. pneumoniae strains tested which had been isolated in Japan, USA and Europe.