Emerging fluoroquinolone-non-susceptible group A streptococci in two different paediatric populations

Clonal emergence of group A streptococci (GAS) with reduced susceptibility to fluoroquinolones (FQs) has been increasingly reported. Non-susceptibility is associated with various point mutations in the target-encoding genes and has only been described in a few emm types. We used a well-characterised GAS clinical paediatric collection from Brussels (Belgium) and Brasília (Brazil) to analyse the molecular basis of FQ non-susceptibility. GAS strains were tested for ciprofloxacin susceptibility and were screened for mutations in DNA gyrase- and topoisomerase IV-encoding genes. Genetic relationships between the different emm types were assessed by phylogenetic analysis of the whole surface-exposed part of the M protein. A high proportion (22.5%) of ciprofloxacin-non-susceptible isolates (minimal inhibitory concentration > or = 2mg/L) was found among the Belgian strains. They belonged mostly to emm type 6 (87%). In Brazil, 6% of the isolates, belonging to seven distantly related emm types, were non-susceptible. Our phylogenetic analysis showed that non-susceptibility may arise in various genetic backgrounds. Sequence comparison of the quinolone resistance-determining regions (QRDRs) of the ParC- and ParE-encoding genes from susceptible and non-susceptible isolates revealed that most of the mutations were found in both classes of isolates, indicating an emm type-linked polymorphism. In conclusion, we observed a clonal spreading of non-susceptible emm type 6 GAS strains in Brussels and a polyclonal distribution of non-susceptible isolates in Brazil. All the Brazilian and Belgian emm type 6 strains displayed a S79A/F mutation in parC that convincingly explains the non-susceptible phenotype.