Pneumococcal Carriage in Children under Five Years in Uganda-Will Present Pneumococcal Conjugate Vaccines Be Appropriate?

BACKGROUND

Pneumonia is the major cause of death in children globally, with more than 900,000 deaths annually in children under five years of age. Streptococcus pneumoniae causes most deaths, most often in the form of community acquired pneumonia. Pneumococcal conjugate vaccines (PCVs) are currently being implemented in many low-income countries. PCVs decrease vaccine-type pneumococcal carriage, a prerequisite for invasive pneumococcal disease, and thereby affects pneumococcal disease and transmission. In Uganda, PCV was launched in 2014, but baseline data is lacking for pneumococcal serotypes in carriage.

OBJECTIVES

To study pneumococcal nasopharyngeal carriage and serotype distribution in children under 5 years of age prior to PCV introduction in Uganda.

METHODS

Three cross-sectional pneumococcal carriage surveys were conducted in 2008, 2009 and 2011, comprising respectively 150, 587 and 1024 randomly selected children aged less than five years from the Iganga/Mayuge Health and Demographic Surveillance Site. The caretakers were interviewed about illness history of the child and 1723 nasopharyngeal specimens were collected. From these, 927 isolates of S. pneumoniae were serotyped.

RESULTS

Overall, the carriage rate of S. pneumoniae was 56% (957/1723). Pneumococcal carriage was associated with illness on the day of the interview (OR = 1.50, p = 0.04). The most common pneumococcal serotypes were in descending order 19F (16%), 23F (9%), 6A (8%), 29 (7%) and 6B (7%). One percent of the strains were non-typeable. The potential serotype coverage rate for PCV10 was 42% and 54% for PCV13.

CONCLUSION

About half of circulating pneumococcal serotypes in carriage in the Ugandan under-five population studied was covered by available PCVs.

Cinobufagin Modulates Human Innate Immune Responses and Triggers Antibacterial Activity

The traditional Chinese medicine Chan-Su is widely used for treatment of cancer and cardiovascular diseases, but also as a remedy for infections such as furunculosis, tonsillitis and acute pharyngitis. The clinical use of Chan-Su suggests that it has anti-infective effects, however, the mechanism of action is incompletely understood. In particular, the effect on the human immune system is poorly defined. Here, we describe previously unrecognized immunomodulatory activities of cinobufagin (CBG), a major bioactive component of Chan-Su. Using human monocyte-derived dendritic cells (DCs), we show that LPS-induced maturation and production of a number of cytokines was potently inhibited by CBG, which also had a pro-apoptotic effect, associated with activation of caspase-3. Interestingly, CBG triggered caspase-1 activation and significantly enhanced IL-1β production in LPS-stimulated cells. Finally, we demonstrate that CBG upregulates gene expression of the antimicrobial peptides (AMPs) hBD-2 and hBD-3 in DCs, and induces secretion of HNP1-3 and hCAP-18/LL-37 from neutrophils, potentiating neutrophil antibacterial activity. Taken together, our data indicate that CBG modulates the inflammatory phenotype of DCs in response to LPS, and triggers an antibacterial innate immune response, thus proposing possible mechanisms for the clinical effects of Chan-Su in anti-infective therapy.

Streptococcal M1 Strikes by Neutralizing Cathelicidins

Virulent group A streptococci have become a serious threat, with the emergence of the hypervirulent lineage M1T1. In this issue of Cell Host & Microbe, LaRock et al. (2015), uncover a role for the streptococcal M1 protein in neutralizing a key human antimicrobial peptide, cathelicidin.

Unaltered pneumococcal carriage prevalence due to expansion of non-vaccine types of low invasive potential 8years after vaccine introduction in Stockholm, Sweden

OBJECTIVE

To evaluate the carriage prevalence, serotype distribution, and antibiotic resistance for pneumococcal carriage isolates collected 4-8years after introduction of pneumococcal conjugate vaccines (PCVs) in Stockholm, Sweden, and to identify risk factors for carriage and calculate the invasive disease potential for emerging serotypes.

METHODS

Nasopharyngeal aspirates were collected from 3024 children aged 0-<5years at regular visits at 23 Child Health Centers in Stockholm County in 2011-2015, and from 787 parents in 2014-2015. The invasive disease potential was calculated for serotypes using invasive disease isolates from 824 patients of all ages identified in the Stockholm County during the same time period as the carriage isolates.

RESULTS

A total carriage prevalence of 30% did not change during the study period. Non-vaccine types (NVT) dominated (94% by 2015) and the most common serotypes in descending order were 11A, 23B, 35F and 21. Risk factors for carriage were: age ⩾3months-<3years, having siblings, attending day-care and having travelled abroad the last 3months. Antibiotic resistance remained low. The invasive disease potential was high for NVT 8, 9N, 12F, and 22F, while low for a majority of emerging NVTs in carriage.

CONCLUSION

The carriage prevalence remained the same 4-8years after vaccine introduction, but serotype replacement became almost complete. A majority of emerging NVTs in carriage showed a low invasive disease potential. Carriage studies are an important complement to invasive disease surveillance to understand the full effect of PCV vaccine programs.

The crystal structure of the major pneumococcal autolysin LytA in complex with a large peptidoglycan fragment reveals the pivotal role of glycans for lytic activity

The pneumococcal autolysin LytA is a key virulence factor involved in several important functions including DNA competence, immune evasion and biofilm formation. Here, we present the 1.05 Å crystal structure of the catalytic domain of LytA in complex with a synthetic cell-wall-based peptidoglycan (PG) ligand that occupies the entire Y-shaped substrate-binding crevice. As many as twenty-one amino-acid residues are engaged in ligand interactions with a majority of these interactions directed towards the glycan strand. All saccharides are intimately bound through hydrogen bond, van der Waals and CH-π interactions. Importantly, the structure of LytA is not altered upon ligand binding, whereas the bound ligand assumes a different conformation compared to the unbound NMR-based solution structure of the same PG-fragment. Mutational study reveals that several non-catalytic glycan-interacting residues, structurally conserved in other amidases from Gram-positive Firmicutes, are pivotal for enzymatic activity. The three-dimensional structure of the LytA/PG complex provides a novel structural basis for ligand restriction by the pneumococcal autolysin, revealing for the first time an importance of the multivalent binding to PG saccharides.

Pneumococcal meningitis is promoted by single cocci expressing pilus adhesin RrgA

Streptococcus pneumoniae (pneumococcus) is the primary cause of bacterial meningitis. Pneumococcal bacteria penetrates the blood-brain barrier (BBB), but the bacterial factors that enable this process are not known. Here, we determined that expression of pneumococcal pilus-1, which includes the pilus adhesin RrgA, promotes bacterial penetration through the BBB in a mouse model. S. pneumoniae that colonized the respiratory epithelium and grew in the bloodstream were chains of variable lengths; however, the pneumococci that entered the brain were division-competent, spherical, single cocci that expressed adhesive RrgA-containing pili. The cell division protein DivIVA, which is required for an ovoid shape, was localized at the poles and septum of pneumococcal chains of ovoid, nonseparated bacteria, but was absent in spherical, single cocci. In the bloodstream, a small percentage of pneumococci appeared as piliated, RrgA-expressing, DivIVA-negative single cocci, suggesting that only a minority of S. pneumoniae are poised to cross the BBB. Together, our data indicate that small bacterial cell size, which is signified by the absence of DivIVA, and the presence of an adhesive RrgA-containing pilus-1 mediate pneumococcal passage from the bloodstream through the BBB into the brain to cause lethal meningitis.

lytA-based identification methods can misidentify Streptococcus pneumoniae

During surveillance studies we detected, among over 1500 presumptive pneumococci, 11 isolates displaying conflicting or novel results when characterized by widely accepted phenotypic (optochin susceptibility and bile solubility) and genotypic (lytA-BsaAI-RFLP and MLST) identification methods. We aimed to determine the genetic basis for the unexpected results given by lytA-BsaAI-RFLP and investigate the accuracy of the WHO recommended lytA real-time PCR assay to classify these 11 isolates. Three novel lytA-BsaAI-RFLP signatures were found (one in pneumococcus and two in S. mitis). In addition, one pneumococcus displayed the atypical lytA-BsaAI-RFLP signature characteristic of non-pneumococci and two S. pseudopneumoniae displayed the typical lytA-BsaAI-RFLP pattern characteristic of pneumococci. lytA real-time PCR misidentified these three isolates. In conclusion, identification of pneumococci by lytA real-time PCR, and other lytA-based methodologies, may lead to false results. This is of particular relevance in the increasingly frequent colonization studies relying solely on culture-independent methods.

Effects of PCV7 and PCV13 on invasive pneumococcal disease and carriage in Stockholm, Sweden

The effects of pneumococcal conjugated vaccines (PCVs) need to be investigated. In Stockholm County, Sweden, PCV7 was introduced in the childhood immunisation programme in 2007 and changed to PCV13 in 2010.Over 90% of all invasive isolates during 2005-2014 (n=2336) and carriage isolates, 260 before and 647 after vaccine introduction, were characterised by serotyping, molecular typing and antibiotic susceptibility, and serotype diversity was calculated. Clinical information was collected for children and adults with invasive pneumococcal disease (IPD).The IPD incidence decreased post-PCV7, but not post-PCV13, in vaccinated children. Beneficial herd effects were seen in older children and adults, but not in the elderly. The herd protection was more pronounced post-PCV7 than post-PCV13. PCV7 serotypes decreased. IPD caused by PCV13 serotypes 3 and 19A increased post-PCV7. Post-PCV13, serotypes 6A and 19A, but not serotype 3, decreased. The serotype distribution changed in carriage and IPD to nonvaccine types, also in nonvaccinated populations. Expansion of non-PCV13 serotypes was largest following PCV13 introduction. Serotype diversity increased and nonvaccine clones emerged, such as CC433 (serotype 22F) in IPD and CC62 (serotype 11A) in carriage. In young children, meningitis, septicaemia and severe rhinosinusitis, but not bacteraemic pneumonia, decreased.Pneumococcal vaccination leads to expansion of new or minor serotypes/clones, also in nonvaccinated populations.

Respiratory viruses associated with community-acquired pneumonia in children: matched case-control study

BACKGROUND

Community-acquired pneumonia (CAP) is the leading cause of death in children worldwide and a substantial proportion of childhood CAP is caused by viruses. A better understanding of the role of virus infections in this condition is needed to improve clinical management and preventive measures. The aim of the study was therefore to assess the association between specific respiratory viruses and childhood CAP.

METHODS

A case-control study was conducted during 3 years in Stockholm, Sweden. Cases were children aged ≤5 years with radiological CAP. Healthy controls were consecutively enrolled at child health units during routine visits and matched to cases on age and calendar time. Nasopharyngeal aspirates were obtained and analysed by real-time PCR for 15 viruses. Multivariate conditional logistic regression was used to account for coinfections with other viruses and baseline characteristics.

RESULTS

A total of 121 cases, of which 93 cases met the WHO criteria for radiological pneumonia, and 240 controls were included in the study. Viruses were detected in 81% of the cases (n=98) and 56% of the controls (n=134). Influenza virus, metapneumovirus and respiratory syncytial virus were detected in 60% of cases and were significantly associated with CAP with ORs >10. There was no association with parainfluenza virus, human enterovirus or rhinovirus and coronavirus and bocavirus were negatively associated with CAP.

CONCLUSIONS

Our study indicates viral CAP is an underestimated disease and points out hMPV as a new important target for the prevention of childhood CAP.

Transcriptional profiling of UlaR-regulated genes in Streptococcus pneumoniae

The transcriptional regulator UlaR belongs to the family of PRD-containing transcriptional regulators, which are mostly involved in the regulation of carbohydrate metabolism. The role of the transcriptional regulator UlaR in Streptococcus pneumoniae has recently been described [1]. Here, we report detailed genome-wide transcriptional profiling of UlaR-regulated genes in S. pneumoniae D39 and its ∆ulaR derivative, either in the presence of 10 mM ascorbic acid in M17 medium using microarray analysis. 10 mM concentration of ascorbic acid was supplemented to the M17 medium because our lacZ-fusion studies indicated that UlaR acts as a transcriptional activator of its targets in the presence of ascorbic acid and the expression of the ula operon was maximal at a 10 mM ascorbic acid concentration [1]. All transcriptional profiling data of UlaR-regulated genes was deposited to Gene Expression Omnibus (GEO) database under accession number GSE61649.

Uptake of extracellular DNA: competence induced pili in natural transformation of Streptococcus pneumoniae

Transport of DNA across bacterial membranes involves complex DNA uptake systems. In Gram-positive bacteria, the DNA uptake machinery shares fundamental similarities with type IV pili and type II secretion systems. Although dedicated pilus structures, such as type IV pili in Gram-negative bacteria, are necessary for efficient DNA uptake, the role of similar structures in Gram-positive bacteria is just beginning to emerge. Recently two essentially very different pilus structures composed of the same major pilin protein ComGC were proposed to be involved in transformation of the Gram-positive bacterium Streptococcus pneumoniae – one is a long, thin, type IV pilus-like fiber with DNA binding capacity and the other one is a pilus structure that was thicker, much shorter and not able to bind DNA. Here we discuss how competence induced pili, either by pilus retraction or by a transient pilus-related opening in the cell wall, may mediate DNA uptake in S. pneumoniae.

Prevalence of community-acquired bacteraemia in Guinea-Bissau: an observational study

Background

The burden of bloodstream infections is insufficiently studied in children in Africa and many healthcare facilities lack the capacity to identify invasive disease. Often studies have been limited to febrile patients or patients admitted to hospital.

Methods

Blood cultures and malaria diagnostics was performed on 372 consecutive children presenting with tachycardia and/or fever to a referral paediatric emergency department in Bissau, Guinea-Bissau. Bacterial species detection, antimicrobial susceptibility testing and molecular typing were performed. The capacity of clinical parameters to identify bacteraemia was evaluated.

Results

The prevalence of bloodstream infection was 12% (46/372) and in 46% (21/46) of the infections the child was non-febrile at presentation to the hospital. The predictive value for bacteraemia was poor for all assessed clinical parameters. Staphylococcus aureus accounted for 54% (26/48) of the isolates followed by non-typhoidal Salmonella, 10% (5/48), Streptococcus pneumoniae, 8% (4/48), and Salmonella Typhi, 6% (3/48). Among S. aureus there was a large diversity of spa types and 38% produced Pantone-Valentine leukocidin. Antibiotic resistance was low, however two out of three Klebsiella pneumoniae isolates produced extended-spectrum beta-lactamases. Malaria was laboratory confirmed in only 5% of the children but 64% (237/372) received a clinical malaria diagnosis.

Conclusions

Bacteraemia was common irrespective of the presence of fever among children presenting to the hospital. The high prevalence of Staphylococcus aureus may be due to contamination. There is an imminent need to improve microbiological diagnostic facilities and to identify algorithms that can identify children at risk of bloodstream infections in Africa.

Sinusitis and pneumonia hospitalization after introduction of pneumococcal conjugate vaccine

BACKGROUND AND OBJECTIVE

Streptococcus pneumoniae is a major cause of pneumonia and sinusitis. Pneumonia kills >1 million children annually, and sinusitis is a potentially serious pediatric disease that increases the risk of orbital and intracranial complications. Although pneumococcal conjugate vaccine (PCV) is effective against invasive pneumococcal disease, its effectiveness against pneumonia is less consistent, and its effect on sinusitis is not known. We compared hospitalization rates due to sinusitis, pneumonia, and empyema before and after sequential introduction of PCV7 and PCV13.

METHOD

All children 0 to <18 years old hospitalized for sinusitis, pneumonia, or empyema in Stockholm County, Sweden, from 2003 to 2012 were included in a population-based study of hospital registry data on hospitalizations due to sinusitis, pneumonia, or empyema. Trend analysis, incidence rates, and rate ratios (RRs) were calculated comparing July 2003 to June 2007 with July 2008 to June 2012, excluding the year of PCV7 introduction.

RESULTS

Hospitalizations for sinusitis decreased significantly in children aged 0 to <2 years, from 70 to 24 cases per 100 000 population (RR = 0.34, P < .001). Hospitalizations for pneumonia decreased significantly in children aged 0 to <2 years, from 450 to 366 per 100 000 population (RR = 0.81, P < .001) and in those aged 2 to <5 years from 250 to 212 per 100 000 population (RR = 0.85, P = .002). Hospitalization for empyema increased nonsignificantly. Trend analyses showed increasing hospitalization for pneumonia in children 0 to <2 years before intervention and confirmed a decrease in hospitalizations for sinusitis and pneumonia in children aged 0 to <5 years after intervention.

CONCLUSIONS

PCV7 and PCV13 vaccination led to a 66% lower risk of hospitalization for sinusitis and 19% lower risk of hospitalization for pneumonia in children aged 0 to <2 years, in a comparison of 4 years before and 4 years after vaccine introduction.

UlaR activates expression of the ula operon in Streptococcus pneumoniae in the presence of ascorbic acid

In this study, the regulatory mechanism of the ula (utilization of l-ascorbic acid) operon, putatively responsible for transport and utilization of ascorbic acid in Streptococcus pneumoniae strain D39, is studied. β-Galactosidase assay data demonstrate that expression of the ula operon is increased in the presence of ascorbic acid as compared with the effects of other sugar sources including glucose. The ula operon consists of nine genes, including a transcriptional regulator UlaR, and is transcribed as a single transcriptional unit. We demonstrate the role of the transcriptional regulator UlaR as a transcriptional activator of the ula operon in the presence of ascorbic acid and show that activation of the ula operon genes by UlaR is CcpA-independent. Furthermore, we predict a 16 bp regulatory site (5'-AACAGTCCGCTGTGTA-3') for UlaR in the promoter region of ulaA. Deletion of the half or full UlaR regulatory site in PulaA confirmed that the UlaR regulatory site present in PulaA is functional.

Clinical manifestations of invasive pneumococcal disease by vaccine and non-vaccine types

Pneumococcal conjugated vaccines (PCVs) have shown protection against invasive pneumococcal disease by vaccine serotypes, but an increase in non-vaccine serotype disease has been observed. Type-specific effects on clinical manifestation need to be explored. Clinical data from 2096 adults and 192 children with invasive pneumococcal disease were correlated to pneumococcal molecular serotypes. Invasive disease potential for pneumococcal serotypes were calculated using 165 invasive and 550 carriage isolates from children. The invasive disease potential was lower for non-PCV13 compared to vaccine-type strains. Patients infected with non-PCV13 strains had more underlying diseases, were less likely to have pneumonia and, in adults, tended to have a higher mortality. Furthermore, patients infected with pneumococci belonging to clonal serotypes only expressing non-PCV13 capsules had a higher risk for septicaemia and mortality. PCV vaccination will probably lead to a decrease in invasive pneumococcal disease but an alteration in the clinical manifestation of invasive pneumococcal disease. Genetic lineages causing invasive pneumococcal disease in adults often express non-vaccine serotypes, which can expand after vaccination with an increased risk of infection in patients with underlying diseases.

Improvement of CRB-65 as a prognostic tool in adult patients with community-acquired pneumonia

BACKGROUND

Patients with community-acquired pneumonia (CAP) often require hospitalisation. CRB-65 is a simple and useful scoring system to predict mortality. However, prognostic factors such as underlying disease and blood oxygenation are not included despite their potential to increase the performance of CRB-65.

METHODS

The study included 1172 consecutive patients (830 inpatients, 342 outpatients) with CAP. Mortality, sensitivity, specificity, positive predictive value and negative predictive value, and the area under the receiver operating characteristic (ROC) curve with 95% CI were calculated. Prognostic accuracy was evaluated after adding coexisting illnesses according to the Pneumonia Severity Index (malignancy, heart failure, hepatic, renal and cerebrovascular disease) and pulse oximetry (SpO2).

RESULTS

Mean age was 65 years, 30-day mortality 7% (inpatients 9%, outpatients 1%). Addition of one point for the presence of ≥1 coexisting condition and one point for SpO2 <90% increased the area under the ROC curve of CRB-65 from 0.82 (95% CI 0.77 to 0.85) to 0.87 (95% CI 0.84 to 0.90; p<0.0001).

CONCLUSIONS

Modification of CRB-65 by including hypoxaemia and presence of specified underlying diseases increased the scoring system's prognostic accuracy while retaining its independence of laboratory tests. DS CRB-65 may have the potential to further facilitate site of care decision for patients with CAP.

Clinical efficacy of polyspecific intravenous immunoglobulin therapy in patients with streptococcal toxic shock syndrome: a comparative observational study

BACKGROUND

Streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis are the 2 most severe invasive manifestations caused by group A Streptococcus (GAS). Intravenous immunoglobulin (IVIG) therapy has been suggested as adjunctive treatment with a beneficial effect on mortality. However the clinical evidence is limited. Here we aim to further document the clinical efficacy of administered IVIG therapy in a comparative observational study of well-defined patients with STSS.

METHODS

The effect of IVIG was evaluated in patients with STSS prospectively identified in a nationwide Swedish surveillance study conducted between April 2002 and December 2004. Detailed data on symptoms, severity of disease, treatment, and outcome were obtained from 67 patients. Crude and adjusted analyses with logistic regression were performed.

RESULTS

Twenty-three patients received IVIG therapy compared with 44 who did not. No significant difference in comorbidities, severity of disease, organ failures, or sex was seen, but the IVIG group was slightly younger and had a higher degree of necrotizing fasciitis (56% vs 14%). The primary endpoint was 28-day survival. Adjusted analysis revealed that factors influencing survival in STSS were Simplified Acute Physiology Score II (odds ratio [OR], 1.1; P = .007), clindamycin (OR, 8.6; P = .007), and IVIG (OR, 5.6; P = .030).

CONCLUSIONS

This comparative observational study of prospectively identified STSS patients demonstrates that both IVIG and clindamycin therapy contribute to a significantly improved survival in STSS.

Bacterial vaccines and antibiotic resistance

Spread of antibiotic resistance is mediated by clonal lineages of bacteria that besides being resistant also possess other properties promoting their success. Some vaccines already in use, such as the pneumococcal conjugate vaccines, have had an effect on these successful clones, but at the same time have allowed for the expansion and resistance evolution of previously minor clones not covered by the vaccine. Since resistance frequently is horizontally transferred it will be difficult to generate a vaccine that covers all possible genetic lineages prone to develop resistance unless the vaccine target(s) is absolutely necessary for spread and/or disease development. Targeting the resistance mechanism itself by a vaccine is an interesting but hitherto unexplored approach.

Clinical utility of PCR for common viruses in acute respiratory illness

BACKGROUND

Acute respiratory illness (ARI) accounts for a large proportion of all visits to pediatric health facilities. Quantitative real-time polymerase chain reaction (qPCR) analyses allow sensitive detection of viral nucleic acids, but it is not clear to what extent specific viruses contribute to disease because many viruses have been detected in asymptomatic children. Better understanding of how to interpret viral findings is important to reduce unnecessary use of antibiotics.

OBJECTIVE

To compare viral qPCR findings from children with ARI versus asymptomatic control subjects.

METHODS

Nasopharyngeal aspirates were collected from children aged ≤5 years with ARI and from individually matched, asymptomatic, population-based control subjects during a noninfluenza season. Samples were analyzed by using qPCR for 16 viruses.

RESULTS

Respiratory viruses were detected in 72.3% of the case patients (n = 151) and 35.4% of the control subjects (n = 74) (P = .001). Rhinovirus was the most common finding in both case patients and control subjects (47.9% and 21.5%, respectively), with a population-attributable proportion of 0.39 (95% confidence interval: 0.01 to 0.62). Metapneumovirus, parainfluenza viruses, and respiratory syncytial virus were highly overrepresented in case patients. Bocavirus was associated with ARI even after adjustment for coinfections with other viruses and was associated with severe disease. Enterovirus and coronavirus were equally common in case patients and control subjects.

CONCLUSIONS

qPCR detection of respiratory syncytial virus, metapneumovirus, or parainfluenza viruses in children with ARI is likely to be causative of disease; detection of several other respiratory viruses must be interpreted with caution due to high detection rates in asymptomatic children.

Adult zebrafish model for pneumococcal pathogenesis

Streptococcus pneumoniae (pneumococcus) is a leading cause of community acquired pneumonia, septicemia, and meningitis. Due to incomplete understanding of the host and bacterial factors contributing to these diseases optimal treatment and prevention methods are lacking. In the present study we examined whether the adult zebrafish (Danio rerio) can be used to investigate the pathophysiology of pneumococcal diseases. Here we show that both intraperitoneal and intramuscular injections of the pneumococcal strain TIGR4 cause a fulminant, dose-dependent infection in adult zebrafish, while isogenic mutant bacteria lacking the polysaccharide capsule, autolysin, or pneumolysin are attenuated in the model. Infection through the intraperitoneal route is characterized by rapid expansion of pneumococci in the bloodstream, followed by penetration of the blood-brain barrier and progression to meningitis. Using Rag1 mutant zebrafish, which are devoid of somatic recombination and thus lack adaptive immune responses, we show that clearance of pneumococci in adult zebrafish depends mainly on innate immune responses. In conclusion, this study provides evidence that the adult zebrafish can be used as a model for a pneumococcal infection, and that it can be used to study both host and bacterial factors involved in the pathogenesis. However, our results do not support the use of the zebrafish in studies on the role of adaptive immunity in pneumococcal disease or in the development of new pneumococcal vaccines.

Emergence of hypervirulent mutants resistant to early clearance during systemic serotype 1 pneumococcal infection in mice and humans

BACKGROUND

Streptococcus pneumoniae serotype 1 has a high likelihood of causing invasive disease. Serotype 1 isolates belonging to CC228 are associated with low mortality, while CC217 isolates exhibit high mortality in patients.

METHODS

Clinical pneumococcal isolates and mutants were evaluated in wild-type C57BL/6 mice, macrophage-depleted mice, neutrophil-depleted mice, and SIGN-R1 knockout mice. In vitro models included binding and phagocytosis by THP-1 cells, capsule measurements, hydrogen peroxide production, and viability assays.

RESULTS

During early systemic infection in mice with serotype 1, large-colony variants appeared in blood. Similar large colonies were found in blood specimens from patients with invasive disease. Large morphotypes contained higher numbers of viable bacteria, grew faster, produced no or little hydrogen peroxide, and contained mutations in the spxB gene. spxB mutants were considerably more virulent in wild-type mice, less susceptible to early host clearance than wild-type strains after intravenous infection, but impaired in colonization. spxB mutants were less efficiently phagocytosed by macrophages than wild-type bacteria, which, in contrast to spxB mutants, caused more-severe disease when macrophages or SIGN-R1 were depleted.

CONCLUSIONS

Hypervirulent spxB mutants are selected in both mice and patients and are resistant to early macrophage-mediated clearance.

The basic keratin 10-binding domain of the virulence-associated pneumococcal serine-rich protein PsrP adopts a novel MSCRAMM fold

Streptococcus pneumoniae is a major human pathogen, and a leading cause of disease and death worldwide. Pneumococcal invasive disease is triggered by initial asymptomatic colonization of the human upper respiratory tract. The pneumococcal serine-rich repeat protein (PsrP) is a lung-specific virulence factor whose functional binding region (BR) binds to keratin-10 (KRT10) and promotes pneumococcal biofilm formation through self-oligomerization. We present the crystal structure of the KRT10-binding domain of PsrP (BR_187–385) determined to 2.0 Å resolution. BR_187–385 adopts a novel variant of the DEv-IgG fold, typical for microbial surface components recognizing adhesive matrix molecules adhesins, despite very low sequence identity. An extended β-sheet on one side of the compressed, two-sided barrel presents a basic groove that possibly binds to the acidic helical rod domain of KRT10. Our study also demonstrates the importance of the other side of the barrel, formed by extensive well-ordered loops and stabilized by short β-strands, for interaction with KRT10.