Characterisation of in vitro-selected mutants of Ureaplasma parvum resistant to macrolides and related antibiotics.

Resistant mutants of Ureaplasma parvum were selected by serial passages of a susceptible strain in subinhibitory concentrations of different macrolides and related antibiotics (erythromycin, azithromycin, josamycin, quinupristin, quinupristin/dalfopristin, pristinamycin and telithromycin). Mechanisms of resistance were characterised by sequencing portions of genes encoding 23S rRNA and ribosomal proteins L4 and L22. Mutants with significantly increased minimum inhibitory concentrations could be selected with all the selector antibiotics, except quinupristin and pristinamycin. Mutants harboured mutations in domain V of the 23S rRNA gene at nucleotides G2056, G2057 or A2058 (Escherichia coli numbering) and in conserved portions of ribosomal proteins L4 and L22. Most of the mutations were associated with complete loss of macrolide and ketolide activity, whereas streptogramin combinations were less affected.