Nonpneumococcal Strains Recently Recovered from Carriage Specimens and Expressing Capsular Serotypes Highly Related or Identical to Pneumococcal Serotypes 2, 4, 9A, 13, and 23A

Abstract

The polysaccharide capsule is a key virulence factor of Streptococcus pneumoniae. There are numerous epidemiologically important pneumococcal capsular serotypes, and recent findings have demonstrated that several of them are commonly found among nonpathogenic commensal species. Here, we describe 9 nonpneumococcal strains carrying close homologs of pneumococcal capsular biosynthetic (cps) loci that were discovered during recent pneumococcal carriage studies of adults in the United States and Kenya. Two distinct Streptococcus infantis strains cross-reactive with pneumococcal serotype 4 and carrying cps4-like capsular biosynthetic (cps) loci were recovered. Opsonophagocytic killing assays employing rabbit antisera raised against S. infantis US67cps4 revealed serotype 4-specific killing of both pneumococcal and nonpneumococcal strains. An S. infantis strain and two Streptococcus oralis strains, all carrying cps9A-like loci, were cross-reactive with pneumococcal serogroup 9 strains in immunodiffusion assays. Antiserum raised against S. infantis US64cps9A specifically promoted killing of serotype 9A and 9V pneumococcal strains as well as S. oralis serotype 9A strains. Serotype-specific PCR of oropharyngeal specimens from a recent adult carriage study in the United States indicated that such nonpneumococcal strains were much more common in this population than serotype 4 and serogroup 9 pneumococci. We also describe S. oralis and S. infantis strains expressing serotypes identical or highly related to serotypes 2, 13, and 23A. This study has expanded the known overlap of pneumococcal capsular serotypes with related commensal species. The frequent occurrence of nonpneumococcal strains in the upper respiratory tract that share vaccine and nonvaccine capsular serotypes with pneumococci could affect population immunity to circulating pneumococcal strains. IMPORTANCE The distributions and frequencies of individual pneumococcal capsular serotypes among nonpneumococcal strains in the upper respiratory tract are unknown and potentially affect pneumococcal serotype distributions among the population and immunity to circulating pneumococcal strains. Repeated demonstration that these nonpneumococcal strains expressing so-called pneumococcal serotypes are readily recovered from current carriage specimens is likely to be relevant to pneumococcal epidemiology, niche biology, and even to potential strategies of employing commensal live vaccines. Here, we describe multiple distinct nonpneumococcal counterparts for each of the pneumococcal conjugate vaccine (PCV) serotypes 4 and 9V. Additional data from contemporary commensal isolates expressing serotypes 2, 13, and 23A further demonstrate the ubiquity of such strains. Increased focus upon this serological overlap between S. pneumoniae and its close relatives may eventually prove that most, or possibly all, pneumococcal serotypes have counterparts expressed by the common upper respiratory tract commensal species Streptococcus mitis, Streptococcus oralis, and Streptococcus infantis.

Pneumococcal carriage in unvaccinated children at the time of vaccine implementation into the national immunization program in Poland

“…It concerns both sample types, but due to very rich bacterial growth, including many non-pneumococcal α-hemolytic colonies, it was particularly difficult to culture S. pneumoniae from saliva. With large numbers of serotype-carriage events detected exclusively with qPCR, and in the light of reports on non-pneumococcal streptococci expressing the pneumococcal capsular polysaccharides 7 , 49 , we paid particular attention to the specificity of assays. We addressed it by testing for serotype samples negative for S. pneumoniae and excluding the results of assays that generated a positive result (serotype 4 and serotype 5 specific qPCRs) .…”

Naturally acquired antibodies against 7 Streptococcus pneumoniae serotypes in Indigenous and non-Indigenous adults

“…infantis are able to carry capsular polysaccharides cross-reactive to S . pneumoniae and may then contribute to acquisition of natural pneumococcal antibodies [ 57 ]. As prevalence, distribution, and exposure to cross-reactive antigens depends on the environment, lifestyle, and hygienic practices, their role in the development of natural immunity may be more prominent in Indigenous than non-Indigenous communities.…”

Streptococcus pneumoniae carriage studies in adults: Importance, challenges, and key issues to consider when using quantitative PCR-based approaches

“…Direct effects of vaccine Kandasamy et al (2019) and Félix et al Cited studies, whenever possible, included adult populations. Miellet et al 10.3389/fmicb.2023.1122276 Frontiers in Microbiology 03 frontiersin.org 2021,2022), isolation of viable pneumococci from oropharyngeal and saliva samples is often very difficult, if not nearly impossible (Carvalho Mda et al, 2013;Wyllie et al, 2014;Krone et al, 2015;Simões et al, 2016;Wyllie et al, 2016). By contrast in the nasopharynx, particularly in children, pneumococci tend to be present at high density and isolation of viable pneumococci is straightforward (Levine et al, 2012;Arguedas et al, 2020;Almeida et al, 2021).…”