DELETIONS OF TN916-LIKE TRANSPOSONS ARE IMPLICATED IN TETM-MEDIATED RESISTANCE IN PATHOGENIC NEISSERIA

Using the tetM-containing conjugative transposon Tn916 as a mutagenesi s tool, we identified two distinct classes of transposon insertions in the meningococcal chromosome. Class I insertions have an intact copy of Tn916 that appears to have transposed by a novel recombinational me chanism, similar to the transposition of conjugative transposons in Gr am-positive bacteria. Class II insertions were characterized by deleti ons of Tn916 but preservation of the tetM determinant. In addition, we identified Class II Tn916-like insertions in the naturally occurring 25.2MDa tetacontaining plasmids of both Neisseria meningitidis and Nei sseria gonorrhoeae. The truncated Tn916-like insertions appeared to be present in the same site in these two plasmids; however, the deletion s of the transposon were different. Plasmid sequence adjacent to the t runcated transposon in the 25.2 MDa plasmids was found in a tetracycli ne-sensitive N. gonorrhoeae 24.5 MDa conjugative plasmid. These data s uggest that the 25.2 MDa plasmids are the result of one or a series of Class II Tn916-like insertions into 24.5 MDa conjugative plasmids. Cl ass II insertions of Tn916-like transposons are implicated in the diss emination of tetM resistance in pathogenic Neisseria.