Mucosal Infections and Invasive Potential of Nonencapsulated Streptococcus pneumoniae Are Enhanced by Oligopeptide Binding Proteins AliC and AliD

Abstract

Nonencapsulated Streptococcus pneumoniae (NESp) is an emerging human pathogen that colonizes the nasopharynx and is associated with noninvasive diseases such as otitis media (OM), conjunctivitis, and nonbacteremic pneumonia. Since capsule expression was previously thought to be necessary for establishment of invasive pneumococcal disease (IPD), serotype-specific polysaccharide capsules are targeted by currently licensed pneumococcal vaccines. Yet, NESp expressing oligopeptide binding proteins AliC and AliD have been isolated during IPD. Thus, we hypothesize AliC and AliD are major NESp virulence determinants that facilitate persistence and development of IPD. Our study reveals that NESp expressing AliC and AliD have intensified virulence compared to isogenic mutants. Specifically, we demonstrate AliC and AliD enhance murine nasopharyngeal colonization and pulmonary infection and are required for OM in a chinchilla model. Furthermore, AliC and AliD increase pneumococcal survival in chinchilla whole blood and aid in resistance to killing by human leukocytes. Comparative proteome analysis revealed significant alterations in protein levels when AliC and AliD were absent. Virulence-associated proteins, including a pneumococcal surface protein C variant (CbpAC), were significantly downregulated, while starvation response indicators were upregulated in the double mutant relative to wild-type levels. We also reveal that differentially expressed CbpAC was essential for NESp adherence to epithelial cells, virulence during OM, reduction of C3b deposition on the NESp surface, and binding to nonspecific IgA. Altogether, the rise in NESp prevalence urges the need to understand how NESp establishes disease and persists in a host. This study highlights the roles of AliC, AliD, and CbpAC in the pathogenesis of NESp.

Panel 7 – Pathogenesis of otitis media – a review of the literature between 2015 and 2019

“…Neuraminidase (NanA) was also shown to be important in regulation of biofilm formation and in vivo disease [23]. The catalytic pathways of these sialidases were recently investigated in depth by Xiao et al [24] Furthermore, a class of Oligopeptide Binding Proteins, AliA and AliC, can enhance mucosal infection and invasion by non-encapsulated strains [25]. Obviously, the impact of the non-encapsulated strains is potentially profound.…”

“…Although pneumococcal detection during AOM has decreased, two observations need to be taken into account. First, the non-encapsulated strains, expressing pneumococcal surface proteins, such as PspK, have increased in prevalence due to the decrease in pneumococcal vaccine types [18,25]. Second, although pneumococci have decreased as the main cause of AOM, the long-term effects of the PCV vaccines are unknown.…”

“…The chinchilla has been utilized in studies of in-host microbial adaptation with NTHi with respect to the phasevarion [48,61] or nutritional limitation [63]. The infectivity of wild type and mutant NTHi [44] and pneumococcal [18,25] strains have been compared effectively in the chinchilla model. The model has also proved useful in the study of polymicrobial infections by NTHi and the pneumococcus [12] and in the role of fibrin and neutrophil extracellular traps (NETS) in middle ear infection and OM persistence [135].…”

Enhanced safety and immunogenicity of a pneumococcal surface antigen A mutant whole‐cell inactivated pneumococcal vaccine

“…One approach to combat serotype replacement is the further expansion of PCV valency, but this is limited by the complexity and cost of manufacture . Additionally, nonencapsulated S. pneumoniae (or nontypeable) is now being reported as an emerging human pathogen . Nonencapsulated S. pneumoniae strains are primarily isolated in carriage, although they have been detected in patients with non‐IPDs such as otitis media and conjunctivitis, and although extremely rare, invasive nonencapsulated S. pneumoniae disease has been reported .…”

“…Additionally, nonencapsulated S. pneumoniae (or nontypeable) is now being reported as an emerging human pathogen . Nonencapsulated S. pneumoniae strains are primarily isolated in carriage, although they have been detected in patients with non‐IPDs such as otitis media and conjunctivitis, and although extremely rare, invasive nonencapsulated S. pneumoniae disease has been reported . Given the nature of CPS‐based vaccines, they will not offer any protection against disease that is potentially caused by nontypeable strains in the future …”