Background
Group B Streptococcus (GBS) is a major cause of invasive disease in infants. Recent study reported that recurrent iGBS might be more common than initially thought, especially in prematurely born babies or multiples, rendering the need to investigate these cases of recurrent iGBS further.
Methods
We whole-genome sequenced a collection of 119 GBS isolates from suspected recurrent iGBS infections affecting 56 babies (<1yrs) in the UK between 2004 and 2018. Genomic characterisation included identification of serotype, multi-locus sequence type (MLST), antimicrobial resistance genes and SNPs to infer relationships between the strains.
Results
Four serotypes were identified in the dataset: III (71%), Ia (19,8%), V (6,3%) and Ib (2,7%). A total of 11 STs were identified, with 56,8% of the isolates belonging to ST17 (n=63). All iGBS isolates were carrying tetracycline resistance genes, tetM or tetO. Macrolide resistance genes (mefA, msrD, ermB or ermT ) were detected in 27% of the isolates (n=30). 12 isolates also carried the ant(6)-Ia and aph(3')-III genes. In 38 cases, at least two isolates from the same infant were within <7 SNPs difference, indicating persistence of the infecting strain or re-infection from a common source. Comparative analysis with other publicly available data has shown that recurrent iGBS isolates originate from the same genetic pool as other iGBS and GBS colonizing isolates.
Conclusion
In our dataset serotype III ST17 strains were dominant among recurrent iGBS cases. The integration of clinical data, detailed antibiotic treatment information as well as information on maternal GBS carriage would also provide more insight into the reasons why infection recurrence was observed.