Emergence and Global Dissemination of Host-Specific Streptococcus agalactiae Clones

Abstract

To examine the global diversity of Streptococcus agalactiae (group B streptococci [GBS]) and to elucidate the evolutionary processes that determine its population genetics structure and the reported changes in host tropism and infection epidemiology, we examined a collection of 238 bovine and human isolates from nine countries on five continents. Phylogenetic analysis based on the sequences of 15 housekeeping genes combined with patterns of virulence-associated traits identified a genetically heterogeneous core population from which virulent lineages occasionally emerge as a result of recombination affecting major segments of the genome. Such lineages, like clonal complex 17 (CC17) and two distinct clusters of CC23, are exclusively adapted to either humans or cattle and successfully spread globally. The recent emergence and expansion of the human-associated and highly virulent sequence type 17 (ST17) could conceivably account, in part, for the increased prevalence of neonatal GBS infections after 1960. The composite structure of the S. agalactiae genome invalidates phylogenetic inferences exclusively based on multilocus sequence typing (MLST) data and thereby the previously reported conclusion that the human-associated CC17 emerged from the bovine-associated CC67.

Epidemiological surveillance of colonising group B Streptococcus epidemiology in the Lisbon and Tagus Valley regions, Portugal (2005 to 2012): emergence of a new epidemic type IV/clonal complex 17 clone

“…In conclusion, a novel epidemic GBS type IV/CC17 clone seems to be emerging through a putative clonal expansion among neonates and adults, as might have occurred since the 1960s with type III/ST17, an 'epidemic clone' with a rapid global dissemination and adaptation to human neonates [30].…”

“…It is worth noting that ST17 lineage was long considered as a homogeneous epidemic clone, almost exclusively composed by serotype III isolates, and characterised by its rapid global dissemination and successful adaptation to human neonates [30]. The origin of the novel association of CC17 with serotype IV can be due to an exchange of a 35.5 kb DNA segment containing the entire capsule operon, culminating in a type III to type IV capsular switch, as described by Bellais et al [10].…”

Intrapartum GBS screening and antibiotic prophylaxis: a European consensus conference

“…Further molecular characterization of GBS isolates has enhanced epidemiological studies even further. Multilocus sequence typing has clearly revealed the strong association of a homogenous clone with neonatal meningitis: the clonal complex CC-17 classified as Sequence-Type 17 (ST-17), defined as the ''highly virulent'' clone amongst GBS of serotype III [49][50][51][52]. A rapid detection of this ''highly virulent'' clone ST-17 in vaginal specimens in pregnant women would allow the identification of a population of neonates at high risk for GBS disease and may suggest a rigorous follow-up of these infants.…”

On the origin of Group B Streptococcus from disease outbreaks in wild marine fish in Australia

“…Unlike the piscine isolates, the population structure of the other S. agalactiae strains used in this study displays a greater diversity as represented by the multiple distinct clonal complexes identified (CC 1, CC 17, CC 23 and CC 67) (Skov Sorensen et al, 2010;. Contrary to the piscine isolates, the crocodile strain, QMA0336, isolated on a farm in the Northern Territory (Darwin) from a case of necrotizing fasciitis in a captive juvenile Crocodylus porosus (Bishop et al, 2007) is unrelated to the ST-261 group.…”

“…3.1). ST-23 is one of the major successful clones identified worldwide, the serotype Ia is associated in humans (Brochet et al, 2006), serotype III in dairy cattle (Brochet et al, 2006;Skov Sorensen et al, 2010), and it has been isolated from Scottish pinniped also serotype Ia, suggesting a possible transmission from human to grey seals via contaminated surface water (Delannoy et al, 2013). Establishing an unambiguous human origin of the Australian ST-23 serotype Ia in juvenile crocodiles remains to be confirmed (Bishop et al, 2007).…”