RESUMO
Pneumococcal resistance to tetracycline, chloramphenicol, erythromycin and clindamycin is often attributed to carriage of conjugative transposons of the Tn916 family. The less well studied conjugative transposon Tn5253 is a composite transposon consisting of a Tn916-like element inserted within the unrelated Tn5252 element, which has also been associated with chloramphenicol and tetracycline resistance. Here, carriage of the Tn5252 integrase (int(5252)), Tn5252-encoded umuC and umuD homologues and Tn916 integrase (int(916)) was examined among 55 clinical isolates of Streptococcus pneumoniae resistant to one or more of the above mentioned antibiotics. Tn5253-associated genes were common among the antibiotic-resistant S. pneumoniae examined, including members of international clones, although the spectrum of genes and resistances carried was diverse. Analysis of five isolates demonstrated insertion of a Tn5253-related element at the same chromosomal locus but sequence and restriction site diversity. This study shows for the first time a high degree of variability of Tn5253-related elements within clinical isolates of pneumococci. The fact that these elements are prevalent among internationally recognised pandemic clones warrants a more intensive investigation.
