Enhanced invasiveness of bovine-derived neonatal sequence type 17 group B Streptococcus is independent of capsular serotype

Background. A defined geographical area (Oxford, United Kingdom) was investigated for the role of group B Streptococcus (GBS) as a human pathogen. Methods. GBS carriage in pregnant women and invasive disease in neonates and adults 160 years of age was studied over a 3-year period. Multilocus sequence typing and capsular serotyping were used to study 369 isolates of GBS from carriage in pregnant women (n = 190) and invasive disease in neonates (n = 109) and adults > 60 years of age (n=70) Results. A total of 20.3% of pregnant women carried GBS. Invasive GBS disease occurred at a rate of 0.9 cases per 1000 live births and 11 cases per 100,000 population 160 years of age per annum. Four sequence types (STs) (ST-17, ST-19, ST-23, and ST-1) that were identified with use of multilocus sequence typing accounted for 150% of carried and invasive strains. A single sequence type (ST-17), previously shown to be phylogenetically of bovine origin, was significantly associated with increased invasiveness in neonates (P = .00002), and this was independent of capsular serotype III. In contrast, among adults 160 years of age, no STs exhibited increased invasiveness, compared with STs carried in pregnant women. Conclusions. Enhanced invasiveness associated with ST-17 is specific to neonates and is independent of capsular serotype.