Expansion and Evolution of Streptococcus pneumoniae Serotype 19A ST320 Clone as Compared to Its Ancestral Clone, Taiwan19F-14 (ST236)

Abstract

Background. The Streptococcus pneumoniae serotype 19A sequence type (ST) 320 clone, derived from an international Taiwan19F-14 (ST236) clone, has become prevalent in many countries.Methods. The dynamics of invasive pneumococcal disease (IPD) were determined using the database of the National Notifiable Disease Surveillance System in Taiwan. The virulence of 19A ST320 and Taiwan19F-14 (ST236) were assessed in mice. By constructing an isogenic serotype 19F variant of the 19A ST320 strain (19F ST320), we analyzed the role of capsular type and genetic background on the difference in virulence between 19A ST320 and Taiwan19F-14 (ST236).Results. Between 2008 and 2011, IPD due to serotype 19A increased from 2.1 to 10.2 cases per 100 000 population (P