Changing Epidemiology of Group B Streptococcus Susceptibility to Fluoroquinolones and Aminoglycosides in France

Abstract

Group B Streptococcus (GBS) is the leading cause of neonatal invasive infections and an emerging pathogen in the elderly. Our objectives were to describe the evolution of GBS resistance to antibiotics in France and to investigate the emergence of fluoroquinolone (FQ)-resistant isolates. A total of 8,757 unrelated GBS isolates were collected and tested for antibiotic susceptibility from 2007 to 2014 according to EUCAST recommendations. All isolates were susceptible to penicillin G, amoxicillin, and vancomycin. Resistance to macrolides decreased from 47.0% to 30.0%, whereas high-level resistance to aminoglycosides, especially amikacin, increased from 6.4% to 8.8% and 24 isolates (0.3%) were highly resistant to gentamicin. FQ resistance gradually increased from 0.2% in 2007 (n = 1) to 1.5% in 2014 (n = 18, P < 0.01). Capsular polysaccharide (CPS) genotyping, multilocus sequence typing, and sequencing of the quinolone resistance-determining region (QRDR) showed that GBS isolates of sequence type 19 (ST-19) CPS type V were largely overrepresented in FQ-resistant isolates (n = 30, 45.5%). All 30 strains displayed the same QRDR mutations and were often associated with cross-resistance to macrolides (93.3%) and gentamicin (30%). In conclusion, we report the rise of FQ- and aminoglycoside-resistant GBS in France over an 8-year study period, an evolution likely linked to the clonal expansion of ST-19 CPS V-resistant isolates. This study emphasizes the need for a continuous surveillance of GBS epidemiology and antibiotic susceptibility.

FIG 1

GBS antibiotic resistance over the 8-year study period. Resistance to erythromycin, amikacin, levofloxacin and gentamicin of the 5,302 GBS colonizing isolates (solid line) and the 3,455 GBS isolates responsible for infection (dashed line) collected and routinely tested from 2007 to 2014 is shown. Filled triangles, erythromycin; filled squares, amikacin; filled diamonds: levofloxacin; filled circles: gentamicin.

FIG 2

Molecular typing of FQ-nonsusceptible GBS isolates over the 8-year study period. CPS genotyping and MLST were performed on the 66 FQ-nonsusceptible GBS isolates.