Tetracycline resistance genes of ureaplasmas

Abstract

In the medical setting, limited information is available on antimicrobial susceptibilities and resistance development in ureaplasmas. This study addresses tetracycline and doxycycline resistance in clinical isolates of Ureaplasma parvum and Ureaplasma urealyticum. Culture, with species polymerase chain reaction (PCR) confrmatory techniques, was applied to 191 endocervical specimens, collected during the period January-March 2006. Minimum inhibitory concentration (MIC) determinations were performed by microbroth dilution, with tetracycline resistance (tetM), and int-Tn genes were characterised by PCR and sequencing. Sixty-six ureaplasma cultures (35 U. parvum, 9 U. urealyticum, 22 U. parvum and U. urealyticum) were obtained. On screening the ureaplasma cultures, tetM gene regions were demonstrated from tetracycline-susceptible and -resistant ureaplasmas. Seven isolates (six U. parvum and one U. urealyticum) were resistant to tetracycline, with dual doxycycline resistance observed in three strains. Int-Tn gene characterisation of the seven tetracycline-resistant strains revealed that three types were present, indicating that transposons from different origins had integrated into ureaplasma genomes. TetM sequences of fve tetracycline-resistant strains were seen to be highly mosaic in structure. The fnding of transposon and/or tetM regions in all ureaplasma cultures investigated, with, or without, full expression of tetracycline resistance, in conjunction with tetM and int-Tn gene mosaic or diversity, verifes that ureaplasmas undergo extensive genetic exchange of transposon or resistance genes, with concomitant genomic remodelling.