First Report of Streptococcus agalactiae Meningitis in a Non-Pregnant Adult in Italy

Abstract

This study, for the first time in Italy, analyses by WGS a Streptococcus agalactiae strain isolated from a non-pregnant adult affected by Meningitis and without common risk factors. The S. agalactiae strain was classified as a serotype II (SS2), sequence type ST569. Molecular characterization evidenced the presence of resistance genes to tetracycline and macrolide (tet(M) and mre(A)) and several virulence genes coding for adhesion and immune evasion factors (bca, cps family, neu family, scpB, gbs family, pil family and hylB), toxins (cfa/cfb, cyl family), pro-inflammatory factors (lepA), and two homologous genes that contributed to bacterial escape from the host immune system (lmb, luxS). SNP analysis showed 18 different alleles, with 9 missense SNP mutations related to genes involved in cellular metabolism (dhaS, ftsE, ligA, nrdD and secA), virulence (bgrR and galE) and antimicrobial resistance (glpK and mutL). SNPs in glpK and mutL genes might reduce susceptibility to drugs. The SNP analysis highlighted the presence of mutations conferring pathogenicity to the strain. The evidence in this study could explain the development of Meningitis in a healthy patient. This case highlights the importance of using molecular methods to characterize the complete genome of a bacterial species that could seriously affect human health.

Keywords: Streptococcus agalactiae; meningitis; pathogenicity; risk factors; whole genome sequencing.

Figure 1

Minimum spanning of all Streptococcus agalactiae isolates. Phylogenetic tree based on the cgMLST data from publicly available Streptococcus agalactiae serotype II isolates (n  =  1056) of human, animal and environmental origin. Colours represent the different distributions of the sequence types. Each circle indicates an allele profile with lines connecting closely related isolates forming clusters (A). The ST569 (red circle) cluster was composed of four strains, including the one presented in this study. The lines indicate allelic differences (B).