Hyperinvasive Neonatal Group B Streptococcus Has Arisen from a Bovine Ancestor

Abstract

The genetic relatedness and evolutionary relationships between group B streptococcus (GBS) isolates from humans and those from bovines were investigated by phylogenetic analysis of multilocus sequence typing data. The collection of isolates consisted of 111 GBS isolates from cows with mastitis and a diverse global collection of GBS isolates from patients with invasive disease (n ‫؍‬ 83) and carriers (n ‫؍‬ 69). Cluster analysis showed that the majority of the bovine isolates (93%) grouped into one phylogenetic cluster. The human isolates showed greater diversity and clustered separately from the bovine population. However, the homogeneous human sequence type 17 (ST-17) complex, known to be significantly associated with invasive neonatal disease, was the only human lineage found to be clustered within the bovine population and was distinct from all the other human lineages. Split decomposition analysis revealed that the human isolate ST-17 complex, the major hyperinvasive neonatal clone, has recently arisen from a bovine lineage.

Shaping a bacterial genome by large chromosomal replacements, the evolutionary history of Streptococcus agalactiae

“…4). Interestingly, these regions were more diverse in CC67 and singletons ST246 and ST260 that are specific to animal strains (15,17). Because these regions are highly conserved only in human isolates, they may be linked to selective advantages in this host that led to the emergence of the dominant clone.…”

“…Several studies (15)(16)(17) have suggested a role of recombinational replacements in the genome evolution of S. agalactiae, although such exchanges never have been reported under laboratory conditions. To test whether chromosomal fragments could be transferred and exchanged between different S. agalactiae isolates, we assessed the transfer of an erythromycin marker (Erm R ) inserted at 30 different locations (I-1 to I-30) in the chromosome of strain NEM316 belonging to CC23.…”

“…Analyses of MLST data from different geographic regions showed that isolates infecting and colonizing neonates cluster mainly in five clonal complexes (CCs), of which CC17 is a major hyperinvasive neonatal clone (14). A marked diversity observed within CCs suggested the importance of recombinational exchanges (15)(16)(17). Accordingly, it was proposed that the horizontal transfer of genes involved in the synthesis of the capsular polysaccharide, a major virulence factor, occurs under natural conditions (18).…”

HumanStreptococcus agalactiaeIsolate in Nile Tilapia (Oreochromis niloticus)

“…Many researchers believe that GBS serotype does not correlate with evolutionary relationships. Strains of different serotypes and sequence types often share more genes than strains of the same serotype and contain carried and invasive strains, traits suggestive of opportunistic pathogenicity (9,11,12).…”

“…Acquisition of bovine GBS by humans has been proposed as 1 plausible explanation (9). Human and bovine GBS isolates have been considered genetically distinct populations (10) and as related populations arising from a common ancestor, presumably bovine (1,9).…”