A molecular analysis of Greek and UK Haemophilus influenzae conjugative resistance plasmids.

Antibiotic resistance in Haemophilus influenzae has been associated with the presence of large, chromosomally integrated, conjugative plasmids. The plasmids of 10 beta-lactamase-positive, ampicillin-resistant strains, two from the UK and eight from Greece, were investigated. Plasmids were detected and isolated after transfer to a rec-deficient recipient. Purified whole plasmid was used as probe. In addition a 12 kb PstI fragment containing the putative point of recircularization in one plasmid, p1056, was cloned and used as a probe. All plasmids shared a high degree of sequence homology suggesting that plasmids of diverse geographical origin are highly related. All plasmids also shared sequence homology with the 12 kb PstI fragment containing the point of recircularization, suggesting that the sequences involved in excision and recircularization are conserved.