In vitro exchange of fluoroquinolone resistance determinants between Streptococcus pneumoniae and viridans streptococci and genomic organization of the parE-parC region in S-mitis

Transfer of fluoroquinolone (FQ) resistance determinants between Streptococ cus pneumoniae and viridans streptococci was explored by transformation in vitro, One-step FQ-resistant parC mutants were selected, and resistance cou ld be transferred from DNA from S. oralis, S. mitis, S. sanguis, and S. con stellatus to S. pneumoniae, with frequencies of 10(-3) to <10(-7) in correl ation with the homologies of their quinolone resistance determining region sequences (95%, 91%, 85%, and 81%, respectively). Reciprocal transfers of m utated parC from DNA from S. pneumoniae to S. mitis and S. oralis were also observed, Simultaneous transfer of mutated parC and gyrA genes from S. mit is to S. pneumoniae yielded high-level-resistant pneumococcal transformants in one step at low frequencies, The parE-parC region of the type strain S. mitis 103335(T) had >90% homology with that of S, pneumoniae. The efficien t interspecific transfer of quinolone resistance determinants in vitro lead s us to anticipate their dissemination in the clinical setting.