Plasmids in Actinobacillus actinomycetemcomitans strains isolated from periodontal lesions of patients with rapidly destructive periodontitis

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Abstract
Several strains of Actinobacillus actinomycetemcomitans newly isolated from periodontal lesions of patients with rapidly destructive periodontitis were all shown to posses identical plasmid profiles consisting of 4 plasmids. The largest plasmid, 20 MegaDalton (MDa), was also found in reference strains. Two different methods were used for isolation of the plasmids; the large 20 MDa plasmid (pHRPl) was found using the Kado and Liu method only. The 3 small plasmids of 7.0, 5.2 and 4.0 MDa (pHRP2, pHRP3, pHRP4), respectively, were seen using the Birnboim and Doly method. These plasmids are so far to be regarded as cryptic; no phenotypical characters have been linked to their presence. The large 20 MDa plasmid was found in all strains examined, and may be a genotypical marker for the A. actinomycetemcomitans species.