Characterization of Group B Streptococcus strains isolated from neonatal invasive diseases in Belgium, 2015.

Introduction
Despite advances in preventive strategies, Group B Streptococcal (GBS) disease is still a leading cause of severe neonatal infections. The Belgian National Reference Centre (NRC) routinely performs surveillances of GBS invasive strains. We here provide an overview of bacteriological characteristics of GBS causing invasive diseases in infants during the year 2015.
Methods
All GBS strains isolated from neonatal invasive diseases sent to the NRC during the year 2015 by any laboratory located in Belgium were characterized: capsular polysaccharide (CPS)-typing by agglutination and/or with PCR, pili-typing with PCR, antimicrobial susceptibility testing, and detection of resistance genes with PCR.
Results
A total of 44 GBS strains isolated from neonatal invasive diseases were available: 21 from Early Onset Diseases (EOD), 23 from Late Onset Diseases (LOD). Considering the incidence of GBS infections in Belgium, this collection represents for 2015 about 40% of GBS invasive diseases. Overall, CPS-type III was predominant (54.6%) followed by Ia, Ib, II, V, IV and VI (15.9%, 11.4%, 9.1%, 4.5%, 2.3%, 2.3%). All strains were susceptible to penicillin. Resistance to macrolides and lincosamides was showed in 22.7% of the strains and mainly linked to the presence of Erm genes: ErmB gene alone was expressed in 70% of the strains (n=7), one strain harboured the combination ErmB with MefA genes and another the ErmB with LsaC genes. One resistant strain did not express any of these four genes. About pili-typing, all strains harboured one of the PI-2 variants alone or in combination: the predominant type was PI1, PI2b (36.3%) followed by PI1, PI2a (27.7%), PI2a (25%) and PI2b (11.4%).
Conclusion
The ratio of EOD/LOD described in Belgium in 2015 remains quite stable since a few years. CPS-type and pili-type distributions, and resistance rate to macrolides/lincosamides are quite similar to European and North American observations done during the last decade.