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

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>16μg/ml to norfloxacin. Eight of 10 adult isolates were susceptible to levofloxacin. The 4 infant isolates with norfloxacin MIC>16μg/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 (AU)

Introducción: En los últimos años se ha detectado un aumento de resistencias a fluorquinolonas entre las cepas de Streptococcus pneumoniae. El objetivo de este estudio es realizar la caracterización molecular y vigilancia de la resistencia a fluorquinolonas en aislamientos de Streptococcus pneumoniae en Sevilla. Métodos: La caracterización de las cepas resistentes a norfloxacina se realizó mediante el estudio de las mutaciones en los genes QRDR, estudio de bombas de reflujo con reserpina, serotipado y patrones de electroforesis en campo pulsante (ECP). Resultados: Catorce (5,1%) aislamientos mostraron una CMI a norfloxacino > 16 g/ml. De los 10 aislamientos de adultos, 8 fueron sensibles a levofloxacina. Los 4 aislamientos pediátricos resistentes anorfloxacina fueron sensibles a levofloxacina. Siete de los 12 aislamientos con bajo nivel de resistencia mostraron una mutación en parC, mientras que sólo en una de las dos cepas con resistencia de alto nivel encontramos mutaciones en los genes ParC y GyrA. Los aislamientos que no mostraron tener mutaciones, pero eran resistentes a la norfloxacina, fueron positivos para la reserpina. El serotipado y los patrones de ECP revelaron una considerable heterogeneidad. Obtuvimos 9 perfiles diferentes, 3 de los cuales contenían2 aislamientos cada uno. Dos de los aislamientos con el mismo pulso tipo resultaron ser del mismo paciente. El primer aislamiento mostró una mutación en el parC y el segundo, una mutación adicional en el gyrA. Conclusiones: Aunque la tasa de resistencia a levofloxacina obtenida fue baja (0,7%), es necesaria una vigilancia para prevenir el desarrollo de resistencias in vivo como la que detectamos (AU)

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

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.