The use of molecular hybridization to evaluate the divergence of some altered Rickettsia prowazekii strains.

Molecular DNA/DNA hybridization was used to investigate the degree of divergence of different Rickettsia prowazekii strains, namely strain Breinl, the vaccine strain E, its spontaneous erythromycin-resistant mutant, nitrosoguanidine-induced rifampicin-resistant mutant and a variant of strain E with increased virulence upon mouse lung passaging. Hybridization of highly polymerised rickettsial DNAs was carried out on nitrocellulose filters with in vitro labelled fragments of reference DNA of the Breinl strain. Nucleotide composition of the strains was also studied. The results obtained suggest the high degree of homology of nucleotide sequences in DNAs of R. prowazekii strains under study; the existing differences found are within the intraspecies range.