Of 108 strains of beta-lactamase producing Neisseria gonorrhoeae (PPNG) isolated from urethral discharges, 91 strains contained three plasmids with molecular mass of 2.6, 4.6 and 25 megadalton, while 17 strains had only two plasmids, missing the plasmid of 25 megadalton.
Transformation tests with isolated plasmid DNA from PPNG to E. coli strain revealed that ampicillin resistance was due to the presence of a 4.6 megadalton (7.4 kilobase) plasmid.
Restriction tests with various endonucleases for recognition sites localized in the 4.6 megadalton plasmid, pNG-3A, showed a single site for each of Pst I, Hind III, Ava I, Pvu I, and Bg1 I, and two sites for BamH I. Performing multiple digestion followed by sizing their fragments, restriction map of the plasmid was constructed.
Plasmids from PPNG or other strains isolated and reported in different countries were compared. The beta-lactamase specifying plasmids were vary in size, but restriction endonuclease maps showed marked structural similarities. Restriction endonuclease map of the pNG-3A showed great structural homologies to the portion of the plasmid pMR 0360 which was known to posses the TnA fragment of Tn3.
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