Genomic and phenotypic characterisation of invasive neonatal and colonising group B Streptococcus isolates from Slovenia, 2001-2018

Objectives: Group B Streptococcus (GBS) is the leading cause of invasive neonatal infection in industrialized world . We aimed to genomically and phenotypically characterise invasive GBS isolates in Slovenia from 2001-2018 and compare them with contemporary colonising GBS isolates.Methods: One-hundred-and-fourteen invasive GBS isolates from 101 patients and 71 colonising isolates from 70 pregnant women were analysed for basic clinical characteristics, antimicrobial susceptibility and capsular serotype. Whole-genome sequencing was performed to assign multilocus sequence type (ST) and clonal complex (CC), pathogenicity/virulence factors and genome-based phylogeny. Clustered regularly interspaced short palindromic repeat (CRISPR) analysis was performed for epidemiological typing. Diagnostically important cfb region was analysed for deletions.Results: Among invasive isolates, 41.6% and 58.4% were responsible for early-onset (EOD) and late-onset (LOD) including very late-onset disease (vLOD), respectively. All isolates were susceptible to benzylpenicillin. Overall, 7 serotypes were identified (Ia, Ib, II-V and VIII), serotype III being the predominant (59.6%). Twenty-nine MLST STs were detected that grouped into 6 CCs. Clonal complex-17 was the predominant CC overall (53.2%) and among invasive (67.3%) and non-invasive (32.9%) isolates (p<0.001). It was also more common among LOD (81.4%) compared to EOD (47.6%) (p<0.001). A CRISPR analysis revealed that CC-17 contained the shortest CRISPR loci with the lowest number of spacers. Finally, no deletions were detected in the cfb region.Conclusions: This is the first genomic characterisation of GBS isolates in Slovenia and provides a valuable means for influencing policy changes with regards to implementing universal screening for GBS colonisation in pregnancy.