Molecular epidemiology of fluoroquinolone resistance in invasive clinical isolates of Streptococcus pneumoniae in Seville

Abstract

Introduction: Due to the emergence of drug-resistant pneumococcal isolates, new fluoroquinolones have been recommended for the treatment of pneumococcal infections. The purpose of this study was to establish surveillance, and to conduct molecular characterization, of fluoroquinolone-resistant Streptococcus pneumoniae in Seville.

Method: Norfloxacin-resistant S. pneumoniae isolates were characterized by quinolone resistance-determining region (QRDR) substitutions, reserpine-sensitive efflux, serotype and by pulsed-field gel electrophoresis (PFGE) patterns.

Results: Fourteen isolates (5.1%) showed an MIC>16 μg/ml to norfloxacin. Eight of 10 adult isolates were susceptible to levofloxacin. The 4 infant isolates with norfloxacin MIC>16 μg/ml were susceptible to levofloxacin. Seven of these 12 low-level-resistant isolates had mutations in ParC, while mutations both in ParC and GyrA genes were only detected in one of the two high-level-resistant isolates. All the isolates without QRDR substitutions that remained norfloxacin-resistant were positive for reserpine-inhibited efflux. The serotyping and PFGE revealed significant heterogeneity. We obtained 9 different profiles, 3 of which had two isolates each. Two of the isolates with the same pulsotype were from the same patient. The first isolate showed a mutation in the QRDR of ParC, and the second one had an additional GyrA mutation.

Conclusion: In our study a levofloxacin resistance rate of 0.7% was found among invasive isolates. Although resistance level is low, surveillance is necessary, especially to prevent cases of in vivo resistance development as reported.