Nasopharyngeal microbiome composition associated with Streptococcus pneumoniae colonization suggests a protective role of Corynebacterium in young children

Profiling the nasopharyngeal Microbiome in patients with community-acquired pneumonia caused by Streptococcus pneumoniae: diagnostic challenges and ecological insights

Community-acquired pneumonia (CAP) is a significant health threat for adults. Although conjugate vaccines have reduced pneumococcal CAP incidence in children, Streptococcus pneumoniae-related CAP remains prevalent among older adults. The nasopharynx acts as a reservoir for S. pneumoniae, yet the interplay between this pathogen and the nasopharyngeal microbiome during and after pneumonia remains poorly understood. This study included 61 adult patients diagnosed with pneumococcal CAP and 61 matched healthy controls. An S. pneumoniae-specific PCR, urine antigen tests and bacterial cultures were performed. Nasopharyngeal swabs collected at admission and three months post-infection were analyzed for microbiome dynamics through 16 S rRNA gene amplicon sequencing. 16 S rRNA gene amplicon sequencing revealed Streptococcus spp. in the majority of all nasopharyngeal samples during infection compared to the other diagnostic test performed. While overall bacterial biomass did not differ between groups, patients exhibited higher alpha diversity (p = 0.012) and lower microbiome stability post-infection. Beta diversity analysis distinguished infection from healthy status (p = 0.002). Taxonomic analysis showed similar core microbiota across groups, but Streptococcus spp. was significantly more abundant during infection, particularly in those patients with viral co-infections. Notably, unique significant bacterial interactions were identified both during and after infection, as well as in healthy states. A negative correlation was observed between Corynebacterium and Streptococcus spp. in infected patients, suggesting a potential antagonistic interaction between these taxa. The nasopharyngeal microbiome in patients with pneumococcal CAP demonstrates persistent disruption post-infection, characterized by lower resilience three months after acute illness. Additionally, we identified specific bacterial interplays during and after infection that differed from those in healthy donors. These bacterial dynamics might play critical roles in pathogen colonization resistance and infection prevention. Thus, our findings highlight the need for further investigation into microbial interactions and potential microbiome-based therapies for respiratory infections, particularly in vulnerable populations.

Airway Corynebacterium interfere with Streptococcus pneumoniae and Staphylococcus aureus infection and express secreted factors selectively targeting each pathogen

The composition of the respiratory tract microbiome is a notable predictor of infection-related morbidities and mortalities among both adults and children. Species of Corynebacterium, which are largely present as commensals in the upper airway and other body sites, are associated with lower colonization rates of opportunistic bacterial pathogens such as Streptococcus pneumoniae and Staphylococcus aureus. In this study, Corynebacterium-mediated protective effects against S. pneumoniae and S. aureus were directly compared using in vivo and in vitro models. Pre-exposure to Corynebacterium pseudodiphtheriticum reduced the ability of S. aureus and S. pneumoniae to infect the lungs of mice, indicating a broadly protective effect. Adherence of both pathogens to human respiratory tract epithelial cells was significantly impaired following pre-exposure to C. pseudodiphtheriticum or Corynebacterium accolens, and this effect was dependent on live Corynebacterium colonizing the epithelial cells. However, Corynebacterium-secreted factors had distinct effects on each pathogen. Corynebacterium lipase activity was bactericidal against S. pneumoniae, but not S. aureus. Instead, the hemolytic activity of pore-forming toxins produced by S. aureus was directly blocked by a novel Corynebacterium-secreted factor with protease activity. Taken together, these results suggest diverse mechanisms by which Corynebacterium contribute to the protective effect of the airway microbiome against opportunistic bacterial pathogens.

Corynebacteria from the respiratory microbiota modulate inflammatory responses and associate with a reduced pneumococcal burden in the lungs

Background

Certain species from the normal respiratory tract microbiota have recently been proposed to positively influence human health. Corynebacterium propinquum and C. pseudodiphtheriticum (Corynebacteria) are two Gram-positive species that frequently colonize the upper respiratory tract and strongly associate with a reduced incidence of respiratory tract infections. The specific role of Corynebacteria during respiratory health and disease is, however, largely uncharacterized.

Method

Respiratory tract epithelial cells NCI-H292 and BALB/cByJ mice were inoculated with Corynebacteria (C. propinquum 2018M3 and 2019M4, and C. pseudodiphtheriticum 2019M8 and 2020M12) alone or with subsequent challenge with Streptococcus pneumoniae (pneumococci). The inflammatory response and the bacterial burden of both species over time were determined by Western blot, luciferase assay, cytokine bead array, flow cytometry and viable plate counts on blood agar plates.

Results

Clinical isolates of Corynebacteria were well tolerated by human cells and mice. Corynebacteria induced a transient inflammatory response during healthy conditions in the absence of known pathogens. Pre-exposure or nasal priming with Corynebacteria did not affect subsequent acquisition of pneumococci but were associated with a modulated inflammatory response in vitro and in vivo as well as with a reduced pneumococcal burden in the respiratory tract of mice. This indicates that the presence of C. propinquum or C. pseudodiphtheriticum may protect against severe pneumococcal infections.

Conclusions

In this study, we delineate the role of Corynebacteria from the normal microbiota that epidemiologically associate with respiratory health. We show that the presence of Corynebacteria modulates the inflammatory response to pneumococci and associate with faster decrease in pneumococcal burden, primarily in the lower respiratory tract. Our data indicate that Corynebacteria has potential to protect against severe pneumococcal infections.

Metabolic capabilities are highly conserved among human nasal-associated Corynebacterium species in pangenomic analyses

Corynebacterium species are globally ubiquitous in human nasal microbiota across the lifespan. Moreover, nasal microbiota profiles typified by higher relative abundances of Corynebacterium are often positively associated with health. Among the most common human nasal Corynebacterium species are C. propinquum, C. pseudodiphtheriticum, C. accolens, and C. tuberculostearicum. To gain insight into the functions of these four species, we identified genomic, phylogenomic, and pangenomic properties and estimated the metabolic capabilities of 87 distinct human nasal Corynebacterium strain genomes: 31 from Botswana and 56 from the United States. C. pseudodiphtheriticum had geographically distinct clades consistent with localized strain circulation, whereas some strains from the other species had wide geographic distribution spanning Africa and North America. All species had similar genomic and pangenomic structures. Gene clusters assigned to all COG metabolic categories were overrepresented in the persistent versus accessory genome of each species indicating limited strain-level variability in metabolic capacity. Based on prevalence data, at least two Corynebacterium species likely coexist in the nasal microbiota of 82% of adults. So, it was surprising that core metabolic capabilities were highly conserved among the four species indicating limited species-level metabolic variation. Strikingly, strains in the U.S. clade of C. pseudodiphtheriticum lacked genes for assimilatory sulfate reduction present in most of the strains in the Botswana clade and in the other studied species, indicating a recent, geographically related loss of assimilatory sulfate reduction. Overall, the minimal species and strain variability in metabolic capacity implies coexisting strains might have limited ability to occupy distinct metabolic niches.

IMPORTANCE

Pangenomic analysis with estimation of functional capabilities facilitates our understanding of the full biologic diversity of bacterial species. We performed systematic genomic, phylogenomic, and pangenomic analyses with qualitative estimation of the metabolic capabilities of four common human nasal Corynebacterium species, along with focused experimental validations, generating a foundational resource. The prevalence of each species in human nasal microbiota is consistent with the common coexistence of at least two species. We identified a notably high level of metabolic conservation within and among species indicating limited options for species to occupy distinct metabolic niches, highlighting the importance of investigating interactions among nasal Corynebacterium species. Comparing strains from two continents, C. pseudodiphtheriticum had restricted geographic strain distribution characterized by an evolutionarily recent loss of assimilatory sulfate reduction in U.S. strains. Our findings contribute to understanding the functions of Corynebacterium within human nasal microbiota and to evaluating their potential for future use as biotherapeutics.

Metabolic capabilities are highly conserved among human nasal-associated Corynebacterium species in pangenomic analyses

Corynebacterium species are globally ubiquitous in human nasal microbiota across the lifespan. Moreover, nasal microbiota profiles typified by higher relative abundances of Corynebacterium are often positively associated with health. Among the most common human nasal Corynebacterium species are C. propinquum, C. pseudodiphtheriticum, C. accolens, and C. tuberculostearicum. To gain insight into the functions of these four species, we identified genomic, phylogenomic, and pangenomic properties and estimated the metabolic capabilities of 87 distinct human nasal Corynebacterium strain genomes: 31 from Botswana and 56 from the USA. C. pseudodiphtheriticum had geographically distinct clades consistent with localized strain circulation, whereas some strains from the other species had wide geographic distribution spanning Africa and North America. All species had similar genomic and pangenomic structures. Gene clusters assigned to all COG metabolic categories were overrepresented in the persistent versus accessory genome of each species indicating limited strain-level variability in metabolic capacity. Based on prevalence data, at least two Corynebacterium species likely coexist in the nasal microbiota of 82% of adults. So, it was surprising that core metabolic capabilities were highly conserved among the four species indicating limited species-level metabolic variation. Strikingly, strains in the USA clade of C. pseudodiphtheriticum lacked genes for assimilatory sulfate reduction present in most of the strains in the Botswana clade and in the other studied species, indicating a recent, geographically related loss of assimilatory sulfate reduction. Overall, the minimal species and strain variability in metabolic capacity implies coexisting strains might have limited ability to occupy distinct metabolic niches.

The impact of respiratory infections and probiotic use on the nasal microbiota of frail residents in long-term care homes

Background

Residents in long-term care homes, who tend to be of advanced age and frail, are at increased risk of respiratory infections. The respiratory microbiota is known to change with age, but whether these changes contribute to the risk of infection is not known. Our goal was to determine how the nasal microbiota of frail older adults changes during symptoms of influenza-like illness (ILI) and how this may be impacted by enrolment in a placebo-controlled trial testing the feasibility of administering a Lactobacillus rhamnosus GG probiotic to prevent respiratory infection (2014-2017).

Methods

The microbiome of the nasal (mid-turbinate) of 150 residents of long-term care homes was interrogated using 16S rRNA gene sequencing.

Results

We identified a diverse and individualised microbiota which could be separated into nine distinct clusters based on Bray-Curtis distances. Samples collected during symptoms of ILI differed statistically from those collected pre- and post-cold and influenza season, and we observed decreased temporal stability (as measured by movement between clusters) in individuals who experienced ILI compared to those who did not.

Conclusions

The use of probiotics decreased ILI-induced changes to the microbiota; however, it is not clear whether this decrease is sufficient to prevent respiratory illness.

Achieving pan-microbiome biological insights via the dbBact knowledge base

16S rRNA amplicon sequencing provides a relatively inexpensive culture-independent method for studying microbial communities. Although thousands of such studies have examined diverse habitats, it is difficult for researchers to use this vast trove of experiments when interpreting their own findings in a broader context. To bridge this gap, we introduce dbBact - a novel pan-microbiome resource. dbBact combines manually curated information from studies across diverse habitats, creating a collaborative central repository of 16S rRNA amplicon sequence variants (ASVs), which are assigned multiple ontology-based terms. To date dbBact contains information from more than 1000 studies, which include 1500000 associations between 360000 ASVs and 6500 ontology terms. Importantly, dbBact offers a set of computational tools allowing users to easily query their own datasets against the database. To demonstrate how dbBact augments standard microbiome analysis we selected 16 published papers, and reanalyzed their data via dbBact. We uncovered novel inter-host similarities, potential intra-host sources of bacteria, commonalities across different diseases and lower host-specificity in disease-associated bacteria. We also demonstrate the ability to detect environmental sources, reagent-borne contaminants, and identify potential cross-sample contaminations. These analyses demonstrate how combining information across multiple studies and over diverse habitats leads to better understanding of underlying biological processes.

The microbiota in respiratory tract infections: from association to intervention

PURPOSE OF REVIEW

The respiratory microbiota has a role in respiratory tract infection (RTI) pathogenesis. On the mucosa, the respiratory microbiota interacts with potential pathogenic viruses, bacteria and the host immune system, including secretory IgA (sIgA). This review discusses the role of the respiratory microbiota and its interaction with the (mucosal) immune system in RTI susceptibility, as well as the potential to exploit the microbiota to promote health and prevent RTIs.

RECENT FINDINGS

Recent studies confirm that specific microbiota profiles are associated with RTI susceptibility and during susceptibility and found accompanying RTIs, although clear associations have not yet been found for SARS-CoV-2 infection. sIgA plays a central role in RTI pathogenesis: it stands under control of the local microbiota, while at the same time influencing bacterial gene expression, metabolism and defense mechanisms. Respiratory microbiota interventions are still newly emerging but promising candidates for probiotics to prevent RTIs, such as Corynebacterium and Dolosigranulum species, have been identified.

SUMMARY

Improved understanding of the respiratory microbiota in RTIs and its interplay with the immune system is of importance for early identification and follow-up of individuals at risk of infection. It also opens doors for future microbiota interventions by altering the microbiota towards a healthier state to prevent and/or adjunctively treat RTIs.

Corynebacterium Species Inhibit Streptococcus pneumoniae Colonization and Infection of the Mouse Airway

The stability and composition of the airway microbiome is an important determinant of respiratory health. Some airway bacteria are considered to be beneficial due to their potential to impede the acquisition and persistence of opportunistic bacterial pathogens such as Streptococcus pneumoniae. Among such organisms, the presence of Corynebacterium species correlates with reduced S. pneumoniae in both adults and children, in whom Corynebacterium abundance is predictive of S. pneumoniae infection risk. Previously, Corynebacterium accolens was shown to express a lipase which cleaves host lipids, resulting in the production of fatty acids that inhibit growth of S. pneumoniae in vitro. However, it was unclear whether this mechanism contributes to Corynebacterium-S. pneumoniae interactions in vivo. To address this question, we developed a mouse model for Corynebacterium colonization in which colonization with either C. accolens or another species, Corynebacterium amycolatum, significantly reduced S. pneumoniae acquisition in the upper airway and infection in the lung. Moreover, the lungs of co-infected mice had reduced pro-inflammatory cytokines and inflammatory myeloid cells, indicating resolution of infection-associated inflammation. The inhibitory effect of C. accolens on S. pneumoniae in vivo was mediated by lipase-dependent and independent effects, indicating that both this and other bacterial factors contribute to Corynebacterium-mediated protection in the airway. We also identified a previously uncharacterized bacterial lipase in C. amycolatum that is required for inhibition of S. pneumoniae growth in vitro. Together, these findings demonstrate the protective potential of airway Corynebacterium species and establish a new model for investigating the impact of commensal microbiota, such as Corynebacterium, on maintaining respiratory health.