Clonal replacement among 19A Streptococcus pneumoniae in Massachusetts, prior to 13 valent conjugate vaccination

Abstract

As part of an ongoing study of the response of the Streptococcus pneumoniae population to conjugate vaccination, we applied multi-locus sequence typing (MLST) to 291 isolates sampled from nasopharyngeal carriage in Massachusetts children. We found 94 distinct sequence types (STs), including 19 that had not been previously recorded, and a xpt allele containing a large insertion. Comparison with a similar sample collected in 2007 revealed no significant overall difference in the ST composition (p=0.51) suggesting that the population has reached a new equilibrium following the introduction of 7 valent vaccination in 2000. Within serotypes, a large and statistically significant increase (p=0.014 Fisher’s Exact test) was noted in the prevalence of the major multiresistant clone ST 320, which is apparently outcompeting ST 199 among serotype 19A strains. This sample will be used as a baseline to study the future evolution of the pneumococcal population in Massachusetts following introduction of vaccines with higher valency.

Population genomics of post-vaccine changes in pneumococcal epidemiology

“…This reduction in disease incidence, while carriage remained nearly unchanged, suggests that the NVT that dominated carriage post-PCV7 were, on average, less invasive than those VT that they replaced 11,12 . Patterns of antibiotic resistance were also observed to change 13,14 ; for instance, several of the epidemic multidrug-resistant clones identified by the Pneumococcal Molecular Epidemiology Network 15 (PMEN) predominately express VT and have consequently declined in frequency since in the introduction of the vaccine.…”

Genetic Analyses of Penicillin Binding Protein Determinants in Multidrug-Resistant Streptococcus pneumoniae Serogroup 19 CC320/271 Clone with High-Level Resistance to Third-Generation Cephalosporins

“…In the United States and other western countries, serotype 19A-ST320, a multidrug-resistant (MDR) clone, has been highly successful after the introduction of the seven-valent pneumococcal conjugate vaccine (PCV7) (4). ST320 is a double-locus variant (DLV) of the originally described Taiwan 19F -14 (Pneumococcal Molecular Epidemiology Network; PMEN14) clone, ST236, from isolates from a Taiwanese hospital in 1997 (5) and has undergone a capsular switch to nonvaccine serotype 19A, likely through recombination that altered the wzy polymerase gene.…”

Mechanisms of genome evolution of Streptococcus

“…In the United States, prevalence of PCV7 serotypes in all age groups decreased from 64% of invasive and 50% of noninvasive isolates in 1999–2000 to 3.8% and 4.2%, respectively, in 2010–2011 (Richter et al, 2013). After the initial PCV7 immunization, the diversity and population structure of carriage pneumococci was also altered (Hanage et al, 2010), even though the overall carriage prevalence has remained constant (Hanage et al, 2011; Wroe et al, 2012). Similar outcomes have been reported in Asia (Kim et al, 2012; Song et al, 2009), Australia (Lehmann et al, 2010), Africa (Nzenze et al, 2013) and Europe (Hanquet et al, 2010; Pichon et al, 2013).…”