Detection of Tn 917 -Like Sequences within a Tn 916 -like Conjugative Transposon (Tn 3872 ) in Erythromycin-Resistant Isolates of Streptococcus pneumoniae

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Abstract
A series of macrolide-lincosamide-streptogramin B (MLS)-resistant pneumococcal isolates of a variety of serotypes was examined and was found to contain Tn 917 -like elements by DNA-DNA hybridization. Like Tn 1545 , Tn 917 also encodes an ermAM gene but does not mediate resistance to other antimicrobial agents. Furthermore, nucleotide sequence analyses of the DNAs flanking three of the Tn 917 -like elements revealed that they were inserted into orf9 of a Tn 916 -like element in a composite transposon-like structure (Tn 3872 ). Other MLS-resistant strains appeared to contain Tn 1545 -like elements that had suffered a deletion of sequences including the aphA-3 sequences responsible for kanamycin resistance. Thus, the MLS resistance phenotype in pneumococci appears to be mediated by the ermAM present on a much wider variety of genetic elements than was previously appreciated.