Emergence of multidrug-resistant clones in levofloxacin-nonsusceptible Streptococcus pneumoniae isolates in Korea

The use of fluoroquinolones to treat respiratory tract infections and pneumonia due to Streptococcus pneumoniae has affected the emergence of resistance to this class of drugs. Increasing pneumococcal resistance to levofloxacin has become a major public health concern. We investigated the prevalence and genetic characteristics of levofloxacin-nonsusceptible S. pneumoniae (LNSP) clinical isolates in Korea. A total of 43 LNSP isolates collected from a national surveillance study at 13 tertiary hospitals between 2008 and 2014 were analyzed for serotype and antimicrobial susceptibilities to 19 antimicrobial agents as well as the quinolone resistance-determining region mutation. Multilocus sequence typing was performed to investigate the genetic relatedness among LNSP isolates. All LNSP isolates (MIC, ≥4 μg/mL) exhibited multidrug-resistant or even extensively drug-resistant (XDR) phenotypes (8 isolates, 18.6%). Most LNSP isolates belonged to sequence type (ST) 8279 and its variants (16 isolates, 37.2%). ST8279 is a double-locus variant of ST156, which is identical to the pneumococcal Spain9V-3 international clone. The high prevalence of nonvaccine types in LNSP isolates could pose significant therapeutic challenges. A limited number of clones dominated the population of LNSP XDR isolates, and homogeneous antimicrobial resistance profiles support the possibility of clonal dissemination of LNSP. More information on the emergence and spread of these LNSP isolates is necessary in order to prevent its spread.