Differentiation of Enterobacter aerogenes from Klebsiellae by Deoxyribonucleic Acid Reassociation

Abstract

Polynucleotide sequence relatedness tests were carried out t o determine the extent of deoxyribonucleic acid (DNA) divergence among species of Klebsiella and Enterobacter aerogenes strains. Labeled, denatured D N A fragments from K. pneumoniae type 2 and E. aerogenes 1627-66 were each incubated with an excess of unlabeled D N A fragments from Klebsielia species and strains of E. aerogenes. Reassociated D N A duplexes were separated from unreacted D N A o n hydroxyapatite. The stability of reassociated D N A duplexes was determined in a series of thermal elutions from hydroxyapatite. Relative reassociation of D N A from 5 Klebsiella strains to K. pneumoniae type 2 was 80 to 91%. In no case did the related D N A duplexes exhibit evidence of greater than 1.2% unpaired bases. Similarly, D N A from 10 strains of E. aerogenes exhibited 8 3 to 100% relative reassociation with D N A from E. aerogenes 1627-66. In this case, 2.2% was the largest amount of unpaired bases within a reassociated D N A duplex. Conversely, only 56% relative relatedness was observed in 18 reactions between klebsiellae and E. aerogenes. In these reactions, related D N A duplexes exhibited an average of 9% unpaired bases. We conclude that klebsiellae and E. aerogenes each are highly related groups of strains Bnd that these two groups have diverged significantly from .one another. An E. cloacae strain exhibited some 40% relative relatedness with some 12% unpaired bases in reactions with K. pneumoniae and E. aerogenes.