Incompatibility and bacteriophage inhibition properties of N-1, a plasmid belonging to the H2 incompatibility group.

N-1, a plasmid isolated from a strain of Shigella flexneri in Japan more than 10 years ago, mediates the phage inhibition phenotype which has recently been found to be characteristic of plasmids of the H2 incompatibility group. Using the criteria of phage inhibition, surface exclusion and incompatibility, the N-1 plasmid is shown to be closely related to H2 plasmids isolated from non-typhoid salmonella and distantly related to H1 plasmids isolated from Salmonella typhi. Plasmids of other incompatibility groups did not show the H2 type of phage inhibition.