Clarification of the structure of the ampicillin-resistance plasmid RSF0885 from Haemophilus influenzae HR-885 serotype b

The nonconjugative ampicillin-resistance plasmid RSF0885 has been reported to be as small as 2.9 MDa and as large as 4.1 MDa with at least two restriction enzyme maps reported. In addition, the source of the original plasmid has been reported to be Haemophilus influenzae and Haemophilus parainfluenzae. Characterization of the source strains and sequencing data of the plasmids revealed that H. influenzae serotype b was the original source strain and that IS1-K in the larger plasmid was presumably acquired when the smaller plasmid was maintained in Escherichia coli in S. Falkow's laboratory during the late 1970s.