Pneumococcal Neuraminidase A (NanA) Promotes Biofilm Formation and Synergizes with Influenza A Virus in Nasal Colonization and Middle Ear Infection

Abstract

Even in the vaccine era, Streptococcus pneumoniae (the pneumococcus) remains a leading cause of otitis media, a significant public health burden, in large part because of the high prevalence of nasal colonization with the pneumococcus in children. The primary pneumococcal neuraminidase, NanA, which is a sialidase that catalyzes the cleavage of terminal sialic acids from host glycoconjugates, is involved in both of these processes. Coinfection with influenza A virus, which also expresses a neuraminidase, exacerbates nasal colonization and disease by S. pneumoniae, in part via the synergistic contributions of the viral neuraminidase. The specific role of its pneumococcal counterpart, NanA, in this interaction, however, is less well understood. We demonstrate in a mouse model that NanA-deficient pneumococci are impaired in their ability to cause both nasal colonization and middle ear infection. Coinfection with neuraminidase-expressing influenza virus and S. pneumoniae potentiates both colonization and infection but not to wild-type levels, suggesting an intrinsic role of NanA. Using in vitro models, we show that while NanA contributes to both epithelial adherence and biofilm viability, its effect on the latter is actually independent of its sialidase activity. These data indicate that NanA contributes both enzymatically and nonenzymatically to pneumococcal pathogenesis and, as such, suggest that it is not a redundant bystander during coinfection with influenza A virus. Rather, its expression is required for the full synergism between these two pathogens.

Glycan‐metabolizing enzymes in microbe–host interactions: the Streptococcus pneumoniae paradigm

“…However, there is also a wealth of evidence to show that the role of Nglycan degradation in the host-pathogen interaction extends beyond nutrition. NanA, as the initiator of complex N-glycan degradation, has been identified as a key virulence factor in S. pneumoniae that contributes to adherence [69,78,[80][81][82], biofilm formation [81][82][83][84], tissue invasion [69,85], colonization [82,[86][87][88][89], persistence [86,87], immune Box 2. NanA, as the initiator of complex N-glycan degradation, has been identified as a key virulence factor in S. pneumoniae that contributes to adherence [69,78,[80][81][82], biofilm formation [81][82][83][84], tissue invasion [69,85], colonization [82,[86][87][88][89], persistence [86,87], immune Box 2.…”

“…The role of NanA in pneumococcal virulence was first investigated following reports that tissues exposed to S. pneumoniae demonstrated removal of Neu5Ac residues and exposure of the underlying glycan receptor [71,72], and that in vitro treatment of chinchilla tracheas with neuraminidase increased S. pneumoniae adherence [74]. Since then, a number of studies have investigated the effect of NanA on pneumococcal adherence; however, results have been conflicting [69,77,78,[80][81][82][83][84]. Inhibition of the neuraminidase activity of NanA has been reported to partially reduce adherence [69,81], but, using truncated versions of NanA, the majority of the contribution of NanA to adherence and invasion has been mapped to its CBM domain [69] (Box 1).…”

“…All of the seven GHs and the ABC transporter involved specifically in N-glycan degradation and transport have been identified as potential virulence factors in at least one signaturetagged mutagenesis (STM) study (Table 1), and many of them have been validated in targeted studies. NanA, as the initiator of complex N-glycan degradation, has been identified as a key virulence factor in S. pneumoniae that contributes to adherence [69,78,[80][81][82], biofilm formation [81][82][83][84], tissue invasion [69,85], colonization [82,[86][87][88][89], persistence [86,87], immune Box 2. Immune evasion or immune activation?…”

Assessing the function of pneumococcal neuraminidases NanA, NanB and NanC inin vitroandin vivolung infection models using monoclonal antibodies

“…Previous studies reported a substantially reduced bacterial burden in the lungs of mice infected intranasally with nan A and/or nan B gene deletion mutant strains and improved host survival [39,40,68]. NanA was shown to contribute to nasopharyngeal colonisation [41,43,68–70]. However, these findings contrast to several other publications, where no such effects were observed in vivo [28,55,71–73].…”

Subversion of host immune responses by otopathogens during otitis media

“…This influences the quorum signaling pathway and can result in the development as well as the establishment of biofilms . Biofilms can be particularly pathogenic in the case of OM, as the infections are polymicrobial and can hence create synergistic reactions, increased growth of organisms, antimicrobial tolerance, increased virulence and persistence, as well as exaggerated levels of exopolysaccharide (EPS) . Biofilms have been found to be associated with adenoid hypertrophy and middle ear effusion .…”