A molecular epidemiological investigation of group B streptococcus
A multilocus sequence typing (MLST) system for group B streptococcus (GBS)
has been developed and validated on a global collection of human GBS strains
isolated from carriage and invasive disease.
A carriage study was performed, over a 3-year period, to establish the
rate of carriage ofGBS in pregnant women in Oxford, UK. Invasive isolates
were collected, prospectively and retrospectively over a similar time period.
Twenty-one percent of women studied were asymptomatic carriers of
GBS. The incidence of invasive GBS was 0.9/1000 live births in neonates and
6.11100,000 population >60 years.
The population structure of GBS is best depicted. using MLST. as a
network of related clusters indicating the presence of recomb inationa I events
occurring in the population that interfere with a tree like branching structure of
A single hypervirulent clone ofGBS (ST-17 complex) is responsible for
an excess of neonatal disease in Oxford (odds ratio 3.4). The possibility that a
factor other than capsular type IIImay be responsible for virulence of this clonal
complex in neonates is raised. Intriguingly this clonal complex was unique
among human lineages in that it has emerged from bovine GBS. It was not
however associated with increased invasiveness amongst adult (> 60 years).
Further study ofthis hypervirulent clone of GBS is likely to contribute to
the understanding of the pathogenesis of neonatal GBS disease.