Prevalence and Clonal Characterization of Streptococcus pyogenes Clinical Isolates with Reduced Fluoroquinolone Susceptibility in Spain

Abstract

The aim of this study was to determine the prevalence and characteristics of non-fluoroquinolone (FQ)-susceptible Streptococcus pyogenes isolates and to study their mechanisms of resistance. We performed a prospective prevalence study with 468 isolates collected from 2005 to 2007 and a retrospective study that was based on the examination of existing data collected from 1999 to 2008. The retrospective study included data for isolates with high-level resistance (HR) to ciprofloxacin (MIC ≥ 32 μg/ml) (HR isolates) and isolates with the same emm types as those reported in the literature with low-level resistance (LR) to ciprofloxacin (MICs, 2 to 8 μg/ml) (LR isolates, n = 205). Genetic characterization of the isolates was performed by means of emm typing and multilocus sequence typing. The prevalence of LR ranged from 1.9% in 2005 to 30.8% in 2007. This increase was mainly due to the circulation of an emm 6 subtype ( emm 6.4) that represented 77.1% of the LR isolates in 2007. Notably, another emm 6 subtype, also detected in 2007 ( emm 6.37), showed coresistance to 14- and 15-membered macrolides mediated by the mefA gene. Only three HR isolates were detected (isolates emm 68.1/ST247/T3,13,B3264, emm 77/ST399/T28, and emm 28/ST52/T28), and all were identified in the retrospective study. Overall, the 673 isolates represented 25 emm types. All LR isolates were clustered into two emm types: emm 6 (six emm 6 subtypes) and emm 75. All the 156 emm 6 isolates had LR, harbored the Ser79/Ala mutation in the parC gene product, and had the same sequence type (ST), ST382. Most (21/33) of the emm 75 isolates had LR, showed the Ser79/Phe plus Asp91/Asn double mutation in the parC gene product, and were ST150. The Asp91/Asn mutation by itself did not confer resistance to FQs.