Background
Fluoroquinolone-resistant (FR) group B Streptococcus (GBS) are rarely reported, although antibiotic resistance has been increasingly highlighted as a concerning threat in GBS.
Methods
Here, we analyzed the genomes of 19 FR GBS isolates using the GBS typer pipeline v1.0.11. FR GBS were isolated in Brazil from 2009 to 2023, from anovaginal samples (AV; 6), semen (10) and invasive disease (3). FR GBS represented 1.8% of all AV isolates, 11.8% of all semen isolates and 7.7% of all invasive isolates.
Results
Most FR GBS (11; 57.9%) were serotype V-ST19, including 9 from semen and 2 from AV. These isolates showed high levofloxacin MIC levels (≥32g/l), had multiple resistance genes (catQ, mefA, tetM), and differed from fluoroquinolone-susceptible ST19-V isolates by harboring exclusive virulence genes (Alp1) and forming a distinct clade in the phylogenetic tree, suggesting they represent a separate sublineage. Other two FR GBS were serotype Ib-ST10 (one from semen and one from AV), while the remaining four represented single serotype-ST combinations (Ia-103, Ia-144, Ib-26, II-28, II-817, III-23, V-2111). Sixteen FR GBS (80%) contained the GyrA S81L substitution combined with the ParC S79F, including all serotype V-ST19 isolates; while the remaining 3 (Ib-26, II-28, III-23) had different substitutions only in parC.
Conclusion
Our results indicate the predominance of a multidrug-resistant sublineage of serotype V-ST19 among FR GBS isolates in Brazil. Besides harboring unique resistance and virulence markers, this sublineage has been successfully circulating during the last decade among pregnant women and, in a higher frequency, among men in our setting.