Nucleotide sequence alignment depicting identical sequence variations in two regions (a and b) of the chromosomal and plasmid-borne oqxAB operon recoverable from K. pneumoniae and Salmonella/E. coli strains, respectively. MGH 78578, KCTC 2242, and CG43: control K. pneumoniae strains. 137-FL, 319-FL, 321-FL, and 324-FL: clinical K. pneumoniae strains isolated in or before the year 1984. pOLA52, pSDB58, pHXY, and E16: plasmids harboring the oqxAB operon, recoverable from Salmonella/E. coli strains. The nucleotide sequence of strain MGH 78578 was used as the reference sequence. Sequence data of the four clinical K. pneumoniae strains were generated in this study. All other data are retrievable from GenBank.