Taxonomy and epidemiology of gram-negative bacterial plasmids studied by DNA-DNA filter hybridization in formamide.

Phylogenetic and epidemiological relatedness among transferable plasmids belonging to the IncC, IncM and IncH incompatibility groups has been studied by DNA-DNA filter hydridization. Hybridization was carried out on nitrocellulose microfilters, at low temperature, in formamide and under paraffin oil. The degree of hybridization among plasmids belonging to the IncC and IncM groups supported the conclusions drawn from genetic classification. Studies on relatedness among plasmids belonging to the IncH group allowed their classification into three phylogenetic sub-groups. Comparison of DNA sequences of three plasmids sharing the same genetic properties and isolated from different bacterial species suggested an epidemiological spread of the same plasmid.