Background: Group B streptococci (GBS) is a leading cause of neonatal invasive disease in most countries. We characterized GBS neonatal infection isolates in Portugal with the aim of identifying antimicrobial resistance among circulating lineages.
Methods: 83 isolates from invasive infections in newborns in Portugal in 2016-2019 were sequenced (Illumina) and relevant information extracted from the draft genomes. Antimicrobial susceptibility was evaluated by disk diffusion.
Results: Serotypes III (61%), Ib (18%) and Ia (14%) accounted for >90% of all isolates. CC17 included 52% of all isolates and was associated with late-onset disease (LOD)(P=0.02). Serotype Ib/CC1 increased in frequency and was associated with early-onset disease (EOD)(P=0.03).
Macrolide resistance (28.9%) increased (P<0.05) associated with the cMLSB phenotype, being overrepresented among serotype Ib/CC1 isolates (P<0.001). We identified a recently emerged sub-lineage of CC17 characterized by the loss of PI-1 (CC17/PI-2b), and simultaneously cMLSB and exhibiting high-level resistance to aminoglycosides.
Conclusions: Although most of the lineages causing neonatal invasive disease are widely disseminated worldwide, we also identified seemingly regionally successful lineages, namely the Ib/CC1 lineage, raising the possibility of an ongoing selection and expansion of GBS lineages.
The emergence and expansion of the Ib/CC1 lineage was documented in invasive infections and carriage in non-pregnant adults, being associated with an increase in macrolide resistance. The expansion of this lineage among neonates may indicate a shift in EOD possibly reflecting maternal colonization. The increase in Ib/CC1 and the emergence of a macrolide resistant CC17 lineage are puzzling given the decrease in overall macrolide consumption in Portugal.