Abstract
Streptococcus agalactiae (Group B Streptococcus, GBS) causes life-threatening infections in newborns and adults with chronic medical conditions. Serotype IV strains are emerging both among carriers and as cause of invasive disease and recent studies revealed two main Sequence Types (STs), ST-452 and ST-459 assigned to Clonal Complexes CC23 and CC1, respectively. Whole genome sequencing of 70 type IV GBS and subsequent phylogenetic analysis elucidated the localization of type IV isolates in a SNP-based phylogenetic tree and suggested that ST-452 could have originated through genetic recombination. SNPs density analysis of the core genome confirmed that the founder strain of this lineage originated from a single large horizontal gene transfer event between CC23 and the hypervirulent CC17. Indeed, ST-452 genomes are composed by two parts that are nearly identical to corresponding regions in ST-24 (CC23) and ST-291 (CC17). Chromosome mapping of the major GBS virulence factors showed that ST-452 strains have an intermediate yet unique profile among CC23 and CC17 strains. We described unreported large recombination events, involving the cps IV operon and resulting in the expansion of serotype IV to CC23. This work sheds further light on the evolution of GBS providing new insights on the recent emergence of serotype IV.
Highlights
Streptococcus agalactiae (Group B Streptococcus, GBS) causes life-threatening infections in newborns and adults with chronic medical conditions
As serotype IV is uncommon among circulating GBS human isolates, we constructed our strain collection selecting type IV GBS from different epidemiological studies and geographical areas to obtain a large collection of serotype IV GBS
The available genome sequences first underwent an in silico typing process to confirm the presence of a canonical serotype IV-specific cps operon, to assign an Sequence Types (STs) and the relative CC to each strain, and to study the distribution of the Pilus Islands (PI)
Summary
Streptococcus agalactiae (Group B Streptococcus, GBS) causes life-threatening infections in newborns and adults with chronic medical conditions. Serotype IV strains are emerging both among carriers and as cause of invasive disease and recent studies revealed two main Sequence Types (STs), ST-452 and ST459 assigned to Clonal Complexes CC23 and CC1, respectively. The human pathogen Streptococcus agalactiae ( referred to as Group B Streptococcus or GBS) is a common cause of life-threatening bacterial infections in neonates and infants[1]. It can cause disease in adults, among older adults (≥65 years) and those with underlying medical conditions such as diabetes, cancer, cirrhosis and HIV infection[2]. GBS is a commensal organism and rectal and vaginal colonization, affecting about 30% of healthy women, is the main risk factor for early onset neonatal infection, occurring between days 0 and 61
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