Biology subjects

Ercoli, G.

Publications and source records attributed to Ercoli, G..

5 recordsLinked to original sources

bioRxiv2025

Biofilm formation during pneumococcal carriage imprints naturally acquired humoral immunity

Streptococcus pneumoniae (Spn) colonization of the nasopharynx is a prerequisite for transmission and invasive disease. To investigate how repeated asymptomatic colonization shapes immunity and influences bacterial traits, we developed the Repeated Asymptomatic Murine Pneumococcal Colonization (RAMPC) model using strains belonging to serotypes: 2 (D39), 3 (WU2), and 4 (TIGR4). Sequential colonization revealed strain- and exposure-order-dependent effects on bacterial burden, with initial colonization yielding robust carriage and subsequent exposures resulting in diminished burden and rapid clearance. Humoral profiling demonstrated antigenic imprinting: the first colonizing strain largely determined IgG and IgA specificity, with minimal diversification after repeated exposures. Reactivity was strongest for biofilm-associated antigens correlating with each strains biofilm-forming capacity. Using TIGR4 mutants deficient in biofilm formation, we confirmed that in vivo aggregate formation drives humoral responses. Human sera from naturally colonized adults mirrored these findings, favoring biofilm antigens independent from capsule. Protection was demonstrated as triple-colonized mice exhibited reduced mortality and bacteremia following pneumococcal pneumonia challenge. Moreover, the initial colonizing strain influenced protection against heterologous infection, underscoring the lasting imprint of the biofilm phenotype on immunity. Finally, IgA responses in nasal-associated lymphoid tissue paralleled serum IgA patterns, validating systemic measurements as a proxy for mucosal immunity. Collectively, these results reveal that biofilm formation during colonization is a key determinant of humoral immunity and protection, providing insight into pneumococcal biology and informing strategies to design next-generation interventions. Author summaryStreptococcus pneumoniae (Spn) is a leading cause of pneumonia, meningitis, and sepsis, yet its primary lifestyle is asymptomatic colonization of the nasopharynx. Understanding how colonization shapes immunity and bacterial physiology is critical for predicting disease risk and improving future vaccines. Using a novel murine model of repeated colonization and human sera from naturally colonized adults, we show that humoral immunity is strongly biased toward antigens expressed during biofilm growth, the predominant mode of Spn in the nasopharynx, rather than planktonic forms. This response is strain-dependent and imprinted by the first colonizing strain, influencing subsequent exposures and protection against pneumonia. Importantly, biofilm formation, not capsule, drives immune recognition revealing a key link between bacterial physiology and host immunity. These findings provide fundamental insight into pneumococcal biology and the host response, suggesting that targeting biofilm-associated antigens may improve vaccine design or strategies to prevent transmission and invasive disease.

microbiology↗

bioRxiv2025

Streptococcus pneumoniae accessory capsular genes modulate fitness, pathogenicity and immune evasion

Globally, Streptococcus pneumoniae disproportionally affects children in resource-poor settings, older adults and people living with HIV. Frequently found as an asymptomatic colonizer of the nasopharynx, this versatile pathogen is a prominent cause of pneumonia, meningitis, bacteraemia and otitis media. Recently, a serotype 3 capsule variant (GPSC10-ST700) has expanded in Malawi with enhanced vaccine escape potential. Here, using a mutational and complementation approach, we show that loss of accessory capsular genes in GPSC10-ST700 contribute to increased opsonophagocytic resistance in this lineage. Although originally thought to be nonfunctional pseudogenes, we show that these genes modulate fitness and the global phosphoproteome in serotype 3 strains. These findings highlight that vaccine escape may be mediated through variations in the pneumococcal capsular locus that enhance fitness, pathogenicity and immune evasion, without capsule switching. IMPORTANCEPneumococcal polysaccharide-conjugate vaccines (PCV) target the polysaccharide capsule (CPS), which is a dominant virulence factor. However, current PCVs induce suboptimal protection against serotype 3 strains, which produce a thicker capsule that when released from the bacterial surface, interferes with antibody-mediated bacterial killing and protection. We recently described the clonal expansion of a sequence type (ST) 700-GPSC10 serotype 3 lineage in Malawi post-PCV13 introduction. This lineage is characterized by the absence of at least 6 genes in its cps locus and a distinct antimicrobial resistance (AMR) profile compared to other serotype 3 strains. Here we uncovered a functional role for the accessory capsular genes (acl) in serotype 3, previously considered to be pseudogenes, which modulate capsule production, shedding, serum tolerance, and bacterial fitness. By linking genotype to phenotype, our work provides new insights into the molecular basis of serotype 3 immune evasion, informing the design of more effective pneumococcal vaccines.

microbiology↗

bioRxiv2024

The Streptococcus pneumoniae transcriptome in patient cerebrospinal fluid identifies novel virulence factors required for meningitis

To better understand Streptococcus pneumoniae pathogenesis we performed RNA sequencing on cerebrospinal fluid (CSF) from meningitis patients to identify bacterial genes expressed during invasion of the central nervous system. Comparison to transcriptome data for serotype 1 S. pneumoniae cultured in ex vivo human CSF defined a subset of 57 genes with high expression during human meningitis. Deletion of two of the most highly expressed genetic loci, bgaA (encodes for a {beta}-galactosidase) or the SP_1801-5 putative stress response operon, resulted in S. pneumoniae strains still able to transmigrate the blood brain barrier but which were more susceptible to complement opsonisation and unable to maintain brain infection in a murine meningitis model. In 1144 meningitis patients, infection with bgaA containing S. pneumoniae strains was associated with a higher mortality (22% versus 14% p=0.02). These data demonstrate that direct bacterial RNAseq from CSF can identify previously undescribed S. pneumoniae virulence factors required for meningitis pathogenesis.

microbiology↗

bioRxiv2023

Essential role of proline synthesis and the one-carbon metabolism pathways for systemic virulence of Streptococcus pneumoniae

Previous virulence screens have indicated potential roles during Streptococcus pneumoniae infection for the one-carbon metabolism pathway component Fhs and proline synthesis mediated by ProABC. To define how these metabolic pathways affect S. pneumoniae virulence we have investigated phenotypes and transcription profiles of {Delta}fhs and {Delta}proABC strain mutants. S. pneumoniae capsular serotype 6B BHN418 {Delta}fhs and {Delta}proABC mutant strains were markedly reduced virulence in mouse models of systemic infection and pneumonia, but were still able to colonise the nasopharynx. Although the {Delta}fhs and {Delta}proABC mutant strains grew normally in complete media, both mutant strains had markedly impaired growth in chemically defined medium, human serum and human CSF. The {Delta}proABC strain also had impaired growth under conditions of osmotic and oxidative stress. When transferred to the serotype 2 D39 S. pneumoniae strain background, the {Delta}fhs mutation replicated the virulence and growth in serum phenotype of the BHN418 mutation. In contrast, the D39 {Delta}proABC mutant could cause septicaemia and grow in human serum, indicating the role of this genetic locus during virulence is strain-specific. In human sera the {Delta}fhs and {Delta}proABC mutants both had major derangements in global gene transcription affecting multiple but different metabolic pathways, identifying the corresponding S. pneumoniae metabolic functions affected by these genes under infection-related conditions. Our data demonstrate an essential role for the S. pneumoniae one- carbon metabolism and a strain-conditional role for proline biosynthesis for growth in physiological fluids and therefore systemic infection, and further demonstrate the vital importance of bacterial metabolism for disease pathogenesis. ImportanceRapid adaptation to grow within the physiological conditions found in the host environment is an essential but poorly understood virulence requirement for systemic pathogens such as Streptococcus pneumoniae. We have now demonstrated an essential role for the one-carbon metabolism pathway and a conditional role depending on strain background for proline biosynthesis for S. pneumoniae growth in serum or CSF and therefore for systemic virulence. RNAseq data demonstrated that loss of one carbon metabolism or proline biosynthesis both have profound but differing effects on S. pneumoniae metabolism in human serum, identifying the metabolic processes dependent on each pathway during systemic infection. These data provide a more detailed understanding of the adaptations required by systemic bacterial pathogens in order to cause infection, and demonstrate that the requirement for some of these adaptations vary between strains from the same species and could therefore underpin strain variations in virulence potential.

microbiology↗

bioRxiv2022

Diurnal differences in intracellular replication within splenic macrophages correlates with the outcome of pneumococcal infection.

Circadian rhythms affect the progression and severity of bacterial infections including those caused by Streptococcus pneumoniae, but the mechanisms responsible for this phenomenon remain largely elusive. Following advances in our understanding of the role of replication of S. pneumoniae within a specific subset of splenic macrophages, we sought to investigate events within the spleen that correlate with differential outcomes of invasive pneumococcal infection. Utilising murine invasive pneumococcal disease (IPD) models, here we report that infection during the murine active phase (zeitgeber time; 15h after start of light cycle, 3h after start of dark cycle) resulted in significantly faster onset of moderate septicaemia compared to rest phase (zeitgeber time 3; 3h after start of light cycle) infection. These findings correlated with significantly higher pneumococcal burden within the spleen of active phase-infected mice at early time points compared to rest phase-infected mice. Whole-section confocal microscopy analysis of these spleens revealed that the number of pneumococci is significantly higher exclusively within marginal zone metallophilic macrophages (MMMs), known to allow intracellular pneumococcal replication as a prerequisite step to the onset of septicaemia. Pneumococcal clusters within MMMs were more abundant and increased in size in active phase-infected mice compared to those in rest phase-infected mice which decreased in size over time and were present in a lower percentage of MMMs. This phenomenon preceded significantly higher levels of bacteraemia alongside serum IL-6 and TNF- concentrations in active phase-infected mice following re-seeding of pneumococci into the blood. In summary, these data link the difference in susceptibility to invasive pneumococcal infection to variation in the ability of MMMs to successfully control and digest phagocytosed bacteria. Author summaryCircadian rhythms are present within the majority of multicellular organisms and influence almost all aspects of our physiology. As such, circadian rhythm disorders have been shown to result in an increased susceptibility to certain diseases. The effects of host circadian rhythm have been also mirrored in rodent studies, with the outcome of Streptococcus pneumoniae infection being dependent on the time of challenge. Whilst studies into the functional effects of circadian rhythm on the host immune system are present, knowledge of how these contribute to the control of invasive S. pneumoniae infection are lacking, especially considering the recent breakthrough in understanding the stages of pneumococcal pathogenesis. We show here that mice infected with S. pneumoniae during their active phase developed septicaemia quicker than those infected during their rest phase. We demonstrate that this is likely due to increased replication of pneumococci specifically within a subset of splenic macrophages, which subsequently results in increased numbers of pneumococci in the blood and higher levels of pro-inflammatory cytokines which result in septicaemia. These data provide novel insights into how circadian rhythm influences the immune functionality of the spleen, and how the regulation of function of one macrophage subtype can significantly alter the course of infection.

microbiology↗