High prevalence of multiresistance in levofloxacin-nonsusceptible Streptococcus pneumoniae isolates in Korea.

Korea exhibits the highest rates of multidrug resistance among Streptococcus pneumoniae. The increasing use of levofloxacin has raised concern about the dissemination of levofloxacin resistance in dominant multidrug-resistant (MDR) clones of our pneumococcal population. A total of 50 levofloxacin-nonsusceptible S. pneumoniae (MIC, ≥4 μg/mL) collected from a multihospital network from 1996 to 2006 were analyzed for serotype, antibiotic resistance profile, quinolone resistance-determining region mutation, and multilocus sequence type. Most levofloxacin-nonsusceptible S. pneumoniae (94.0%) exhibited an MDR phenotype. This phenotype was closely associated with a limited number of epidemic MDR clones that are well-known key agents of the global spread of antimicrobial resistance in S. pneumoniae. However, the clonal dissemination of levofloxacin-nonsusceptible S. pneumoniae was rare. Levofloxacin-nonsusceptible clones with nonvaccine serotypes increased during the post-vaccine era in this study. This result suggests that Korean clinicians must be aware of the levofloxacin resistance trend and need to be more prudent for the first choice of fluoroquinolone for empiric treatment of respiratory tract infections in clinical setting. Moreover, the emergence of new clones and their variations may be more frequently associated with resistance under this selective pressure, such as the introduction of a 7-valent pneumococcal conjugate vaccine into our community.