Neonatal host defense against Staphylococcal infections

Epidemiology and clinical presentation of community-acquired Staphylococcus aureus bacteraemia in children under 5 years of age admitted to the Manhiça District Hospital, Mozambique, 2001-2019

Staphylococcus aureus bacteraemia (SAB) is one of the most common bloodstream infections globally. Data on the burden and epidemiology of community-acquired SAB in low-income countries are scarce but needed to define preventive and management strategies. Blood samples were collected from children < 5 years of age with fever or severe disease admitted to the Manhiça District Hospital for bacterial isolation, including S. aureus. Between 2001 and 2019, 7.6% (3,197/41,891) of children had bacteraemia, of which 12.3% corresponded to SAB. The overall incidence of SAB was 56.1 episodes/100,000 children-years at risk (CYAR), being highest among neonates (589.8 episodes/100,000 CYAR). SAB declined significantly between 2001 and 2019 (322.1 to 12.5 episodes/100,000 CYAR). In-hospital mortality by SAB was 9.3% (31/332), and significantly associated with infections by multidrug-resistant (MDR) strains (14.7%, 11/75 vs. 6.9%, 14/204 among non-MDR, p = 0.043) and methicillin-resistant S. aureus (33.3%, 5/15 vs. 7.6%, 20/264 among methicillin-susceptible S. aureus, p = 0.006). Despite the declining rates of SAB, this disease remains an important cause of death among children admitted to MDH, possibly in relation to the resistance to the first line of empirical treatment in use in our setting, suggesting an urgent need to review current policy recommendations.

Prevalence of Staphylococcus spp. from human specimens submitted to diagnostic laboratories in South Africa, 2012-2017

Background

Although staphylococci are commensals of the skin and mucosa of humans and animals, they are also opportunistic pathogens. Some coagulase-negative Staphylococcus spp. (CoNS), such as S. haemolyticus and S. epidermidis, are reported to be zoonotic.

Objectives

The prevalence of coagulase positive (CoPS), CoNS and coagulase-variable Staphylococcus spp. isolated from human clinical cases in South Africa was investigated.

Method

Retrospective records of 404 217 diagnostic laboratory submissions from 2012 to 2017 were examined and analysed in terms of time, place and person.

Results

Of the 32 different species identified, CoPS were the most frequently isolated (74.7%), followed by CoNS (18.9%). Just over half (51.2%) of the Staphylococcus isolates were from males, while females contributed 44.8%. Patients aged 0-4 years contributed the most (21.5%) isolates, with the highest number coming from KwaZulu-Natal (32.8%). Urinary specimens accounted for 29.8% of the isolates reported. There was no variation in the number of Staphylococcus isolates reported in the autumn (25.2%), winter (25.2%), spring (25.1%) and summer (24.5%) seasons.

Conclusion

This study demonstrated the diversity of Staphylococcus spp. isolated from humans and the magnitude of infection, with the most predominant species being S. aureus and S. epidermidis.

Contribution

Although most isolates were CoPS, the isolation of CoNS seen in this study suggests a need to improve infection control measures in a South African context. More research is needed to investigate the determinants of the observed variations in the study.

Increased fecal human beta-defensin-2 expression in preterm infants is associated with allergic disease development in early childhood

Background

This study aimed to investigate whether fecal human beta-defensins (HBD)-2 and eosinophil cationic protein (ECP) expression in preterm infants are associated with allergic disease development by age 2 years.

Methods

Preterm infants' stool samples were collected at the age of 6 and 12 months postnatally. Information regarding medication exposure histories (antibiotics, antipyretics, probiotics) and physician-diagnosed allergic diseases was obtained using age-specific questionnaires and medical records. We compared the 6-month and 12-month fecal HBD-2 and ECP concentrations between the medication exposure and non-exposure group, respectively, and between children who developed allergic diseases and those who did not by 2 years of age. Univariate and multivariable logistic regression analyses were performed to investigate independent variables related to physician-diagnosed allergic diseases by 2 years of age.

Results

Seventy-four preterm infants (gestational age, 31–36 weeks) were included. Fecal HBD-2 levels were significantly increased at 12 months of age among children who developed allergic diseases compared to those who did not (37.18 ± 11.80 ng/g vs. 8.56 ± 4.33 ng/g, P = 0.011). This association was more apparent among allergic children given antibiotics (50.23 ± 16.15 ng/g vs. 9.75 ± 7.16 ng/g, P = 0.008) or antipyretics (46.12 ± 14.22 ng/g vs. 10.82 ± 6.81 ng/g, P = 0.018) during the first year, whereas among allergic children who were previously not exposed to antibiotics or antipyretics, the differences were not significant. Results of the multivariable logistic regression analysis indicated that HBD-2 concentration in 12-month stools was an independent indicator associated with physician-diagnosed allergic diseases by 2 years of age (adjusted odds ratio: 1.03 [95% confidence interval: 1.00–1.05], P = 0.036). Our data revealed a lack of association between fecal ECP and allergic diseases.

Conclusions

We found that preterm infants who expressed high fecal HBD-2 at 12 months of age were associated with physician-diagnosed allergic diseases by the age of 2 years. Further studies are needed to determine the role of fecal HBD-2 in the development of allergic diseases.

Activation of human γδ T cells and NK cells by Staphylococcal enterotoxins requires both monocytes and conventional T cells

Staphylococcal enterotoxins (SE) pose a great threat to human health due to their ability to bypass antigen presentation and activate large amounts of conventional T cells resulting in a cytokine storm potentially leading to toxic shock syndrome. Unconventional T- and NK cells are also activated by SE but the mechanisms remain poorly understood. In this study, the authors aimed to explore the underlying mechanism behind SE-mediated activation of MAIT-, γδ T-, and NK cells in vitro. CBMC or PBMC were stimulated with the toxins SEA, SEH, and TSST-1, and cytokine and cytotoxic responses were analyzed with ELISA and flow cytometry. All toxins induced a broad range of cytokines, perforin and granzyme B, although SEH was not as potent as SEA and TSST-1. SE-induced IFN-γ expression in MAIT-, γδ T-, and NK cells was clearly reduced by neutralization of IL-12, while cytotoxic compounds were not affected at all. Kinetic assays showed that unconventional T cell and NK cell-responses are secondary to the response in conventional T cells. Furthermore, co-cultures of isolated cell populations revealed that the ability of SEA to activate γδ T- and NK cells was fully dependent on the presence of both monocytes and αβ T cells. Lastly, it was found that SE provoked a reduced and delayed cytokine response in infants, particularly within the unconventional T and NK cell populations. This study provides novel insights regarding the activation of unconventional T- and NK cells by SE, which contribute to understanding the vulnerability of young children towards Staphylococcus aureus infections.

Effect of Synergistic Action of Bovine Lactoferrin with Antibiotics on Drug Resistant Bacterial Pathogens

Background and Objectives: The multidrug resistant (MDR) bacterial pathogenic infection is one of the chief worldwide public health threat to humanity. The development of novel antibiotics against MDR Gram negative bacteria has reduced over the last half century. Research is in progress regarding the treatment strategies that could be engaged in combination with antibiotics to extend the duration of these life-saving antibacterial agents. The current study was therefore planned to assess the synergistic effects of bovine lactoferrin (bLF) in combination with different antibiotics that are conventionally used. This synergism would provide a newer therapeutic choice against MDR pathogens. LF is present in mucosal secretions, vastly in milk. LF is considered an important constituent in host defense. In previous reports, LF has been co-administered as a combination antibiotic therapy. Materials and Methods: This study included synergistic (LF + appropriate antibiotic) exposure against 147 locally encountered bacterial pathogens, which were completely characterized strains. The anti-biofilm effects and the outcome of bLF on minimum inhibitory concentrations (MICs) of antibacterials on clinical MDR bacterial pathogens were determined by standard techniques. Results: In our study, synergism of bLF with antibacterial agents were reproducible and found to be significant. LF on its own had an important effect of inhibiting the biofilm production of some significant bacterial pathogens. Conclusion: The results of this study provides useful data on the antibacterial potential of the combination of LF with antibiotics against drug resistant pathogens.

Staphylococcus aureus Bacteremia in Children of Rural Areas of The Gambia, 2008-2015

Staphylococcus aureus bacteremia is a substantial cause of childhood disease and death, but few studies have described its epidemiology in developing countries. Using a population-based surveillance system for pneumonia, sepsis, and meningitis, we estimated S. aureus bacteremia incidence and the case-fatality ratio in children <5 years of age in 2 regions in the eastern part of The Gambia during 2008–2015. Among 33,060 children with suspected pneumonia, sepsis, or meningitis, we performed blood culture for 27,851; of 1,130 patients with bacteremia, 198 (17.5%) were positive for S. aureus. S. aureus bacteremia incidence was 78 (95% CI 67–91) cases/100,000 person-years in children <5 years of age and 2,080 (95% CI 1,621–2,627) cases/100,000 person-years in neonates. Incidence did not change after introduction of the pneumococcal conjugate vaccine. The case-fatality ratio was 14.1% (95% CI 9.6%–19.8%). Interventions are needed to reduce the S. aureus bacteremia burden in The Gambia, particularly among neonates.

Umbilical catheters as vectors for generalized bacterial infection in premature infants regardless of antibiotic use

Introduction. Umbilical catheterization offers unique vascular access that is only possible in the neonatal setting due to unobstructed umbilical vessels from foetal circulation. With the cut of the umbilical cord, two arteries and a vein are dissected, allowing quick and painless catheterization of the neonate. Unfortunately, keeping the umbilical access sterile is challenging due to its mobility and necrosis of the umbilical stump, which makes it a perfect model for vessel catheter colonization analysis.Aim. The aim of this study was to evaluate bacterial colonization of the umbilical catheter, with a focus on the difference between various sections of the catheter, the duration of catheterization, patient status and gestational age.Methodology. We performed bacterial cultures for 44 umbilical catheters, analysing the superficial and deep parts of the catheter separately, and revealed colonization in one-third of cases.Results. One hundred per cent of the colonization occurred in preterm infants, with a shift towards extreme prematurity. The catheters were mainly colonized by coagulase-negative staphylococci. The majority of catheters presented with superficial colonization dominance, and there were no cases of deep colonization. The bacterial strains and their resistance were consistent between the catheter's proximal and distal parts, as well as positive blood cultures. The patients with the most intense bacterial catheter colonization presented with sepsis around removal time or a couple of days later, especially if they were extremely premature and exhibited very low birth weight. Catheterization time did not play a major role.Conclusion. Umbilical catheters are vectors for skin microflora transmission to the bloodstream via biofilm formation, regardless of antibiotic use and the duration of catheterization, especially in preterm neonates.

An underestimated pathogen: Staphylococcus epidermidis induces pro-inflammatory responses in human alveolar epithelial cells

OBJECTIVES

Conventionally regarded as a harmless skin commensal, Staphylococcus epidermidis accounts for the majority of neonatal late-onset sepsis and is shown to be associated with neonatal inflammatory morbidities, especially bronchopulmonary dysplasia. This study addressed the pro-inflammatory capacity of different S. epidermidis strains on human alveolar epithelial cells.

METHODS

A549 cell monolayers were stimulated by live bacteria of S. epidermidis RP62A strain (biofilm-positive) and ATCC 12228 strain (biofilm-negative) at a multiplicity of infection ratio of 10 for 24 h. LPS (100 ng/ml) and Pam3CSK4 (1 µg/ml) were used for comparisons. Cell viability was measured by MTT method. The mRNA and protein expression of inflammatory mediators and toll-like receptor (TLR)-2 were assessed using RT-PCR, immunoassays and immunofluorescence.

RESULTS

Both S. epidermidis strains induced expression of tumor necrosis factor (TNF)-α, IL-1β, interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1, interferon γ-induced protein 10 (IP-10) and intercellular adhesion molecule (ICAM)-1, but not IL-10. The stimulatory effect of RP62A exceeded that of LPS (p < 0.05). RP62A strain showed a trend towards higher induction of pro-inflammatory mediators than ATCC 12228 strain. The co-stimulation with RP62A strain decreased cell viability compared to control and TLR agonists (p < 0.05). RP62A but not ATCC 12228 stimulated mRNA and protein expression of TLR2.

CONCLUSIONS

S. epidermidis drives pro-inflammatory responses in lung epithelial cells in vitro. The pro-inflammatory capacity of S. epidermidis may differ between strains. Biofilm-positive S. epidermidis strain seems to induce more potent pulmonary pro-inflammation than biofilm-negative S. epidermidis strain.

Beyond sepsis: Staphylococcus epidermidis is an underestimated but significant contributor to neonatal morbidity

Staphylococcus epidermidis accounts for the majority of cases of neonatal sepsis. Moreover, it has been demonstrated to be associated with neonatal morbidities, such as bronchopulmonary dysplasia (BPD), white matter injury (WMI), necrotizing enterocolitis (NEC) and retinopathy of prematurity (ROP), which affect short-term and long-term neonatal outcome. Imbalanced inflammation has been considered to be a major underlying mechanism of each entity. Conventionally regarded as a harmless commensal on human skin, S. epidermidis has received less attention than its more virulent relative Staphylococcus aureus. Particularities of neonatal innate immunity and nosocomial environmental factors, however, may contribute to the emergence of S. epidermidis as a significant nosocomial pathogen. Neonatal host response to S. epidermidis sepsis has not been fully elucidated. Evidence is emerging regarding the implication of S. epidermidis sepsis in the pathogenesis of neonatal inflammatory diseases. This review focuses on the interplay among S. epidermidis, neonatal innate immunity and inflammation-driven organ injury.

Modulation of S. epidermidis-induced innate immune responses in neonatal whole blood

BACKGROUND

Coagulase-negative staphylococci (CoNS) such as Staphylococcus epidermidis are highly prevalent pathogens for sepsis in neonates. The interaction between host, environment and pathogenic factors of S. epidermidis are still poorly understood. Our objective was to address the role of several pathogenic factors of S. epidermidis on neonatal cytokine responses and to characterize the influence of three immunomodulatory drugs.

METHODS

We performed an ex-vivo model of S. epidermidis sepsis by assessment of blood cytokine production in neonatal whole blood stimulation assays (ELISA). S. epidermidis strains with different characteristics were added as full pathogen to umbilical cord blood cultures and the influence of indomethacin, ibuprofen and furosemide on neonatal immune response to S. epidermidis was evaluated (Flow cytometry).

RESULTS

Stimulation with S. epidermidis sepsis strains induced higher IL-6 and IL-10 expression than stimulation with colonization strains. Biofilm formation in clinical isolates was associated with increased IL-10 but not IL-6 levels. In contrast, stimulation with mutant strains for biofilm formation and extracellular virulence factors had no major effect on cytokine expression. Notably, addition of ibuprofen or indomethacin to S. epidermidis inoculated whole blood resulted in mildly increased expression of TNF-α but not IL-6, while frusemide decreased the production of pro-inflammatory cytokines, i.e. IL-6 and IL-8.

CONCLUSIONS

The virulence of sepsis strains is coherent with increased cytokine production in our whole-blood in-vitro sepsis model. Biofilm formation and expression of extracellular virulence factors had no major influence on readouts in our setting. It is important to acknowledge that several drugs used in neonatal care have immunomodulatory potential.

New Threats from an Old Foe: Methicillin-Resistant Staphylococcus aureus Infections in Neonates

Methicillin-resistant Staphylococcus aureus (MRSA) is a ubiquitous human inhabitant and one of the important pathogens of neonatal infections. MRSA is associated with significant mortality and morbidity, especially in very immature preterm neonates. Moreover, MRSA may be implicated in adverse long-term neonatal outcomes, posing a substantial disease burden. Recent advances in molecular microbiology have shed light on the evolution of MRSA population structure and virulence factors, which may contribute to MRSA epidemic waves worldwide. Equipped with remarkable genetic flexibility, MRSA has successfully developed resistance to an extensive range of antibiotics including vancomycin, as well as antiseptics. In the face of these new challenges from MRSA, our armamentarium of anti-infective strategies is very limited and largely dependent on prevention measures. Active surveillance cultures followed by decolonization may be a promising approach to control MRSA infections, with its efficacy and safety in the specific population of neonates yet to be addressed by large multicenter studies.

Risk factors for methicillin-resistant Staphylococcus aureus colonization in the neonatal intensive care unit: A systematic review and meta-analysis

CONTEXT

Methicillin-resistant Staphylococcus aureus (MRSA) causes a significant burden of illness in neonatal intensive care units (NICUs) worldwide. Identifying infants colonized with MRSA has become an important infection control strategy to interrupt nosocomial transmission.

OBJECTIVE

Assess risk factors for MRSA colonization in NICUs via a systematic review and meta-analysis.

DATA SOURCES

MEDLINE, Embase, Web of Science, and The Cochrane Library databases were searched from inception through September 2015.

STUDY SELECTION

Studies reporting risk factors for MRSA colonization using noncolonized controls in subspecialty level III or IV NICUs were included.

DATA EXTRACTION

Two authors independently extracted data on MRSA colonization risk factors, study design, and MRSA screening methodology.

RESULTS

Eleven articles were included in the systematic review, with 10 articles analyzed via meta-analysis. MRSA colonization was associated with gestational age <32 weeks (odds ratio [OR], 2.67; 95% confidence interval [CI], 1.35-5.27; P = .01) and birth weight <1,500 g (OR, 2.63; 95% CI, 1.25-5.55; P = .01). Infant sex (P = .21), race (P = .06), inborn status (P = .09), and delivery type (P = .24) were not significantly associated with colonization.

CONCLUSIONS

Very preterm and very-low birth weight infants were identified as having an increased risk for MRSA colonization on meta-analysis. Multifaceted infection prevention strategies should target these high-risk infants to reduce MRSA colonization rates in NICUs.

Protecting the Newborn and Young Infant from Infectious Diseases: Lessons from Immune Ontogeny

Infections in the first year of life are common and often severe. The newborn host demonstrates both quantitative and qualitative differences to the adult in nearly all aspects of immunity, which at least partially explain the increased susceptibility to infection. Here we discuss how differences in susceptibility to infection result not out of a state of immaturity, but rather reflect adaptation to the particular demands placed on the immune system in early life. We review the mechanisms underlying host defense in the very young, and discuss how specific developmental demands increase the risk of particular infectious diseases. In this context, we discuss how this plasticity, i.e. the capacity to adapt to demands encountered in early life, also provides the potential to leverage protection of the young against infection and disease through a number of interventions.

Loss of cutaneous microbial diversity during first 3 weeks of life in very low birthweight infants

Neonatal sepsis (NS) is a frequent problem in neonatal intensive care, especially in preterm and very low birthweight (VLBW) infants. The objective of the study was to characterize the cutaneous bacterial microbiome in VLBW infants treated in the neonatal intensive care unit (NICU). Non-invasive skin microbiome specimens were taken repeatedly from 12 VLBW infants during treatment in NICU starting on the first day of life. All infants received benzylpenicillin and netilmicin during the first 1-5 postnatal days. Samples were also collected from incubators. High cutaneous microbial diversity was present at birth in 11 of 12 of the infants, but the diversity decreased substantially after the first weeks of life in all infants regardless of their infection status. After the loss of diversity, one Staphylococcus operational taxonomic unit dominated the skin microbiome. Recovery of microbial diversity was seen in six of 12 neonates. The microbiome of incubators showed typical environmental bacterial genera. Maternal antibiotic treatment, the aetiology of the preterm birth or being born by C-section did not appear to affect the diversity of skin microbiota at birth, and no correlation was found between cutaneous microbiome and NS.

Potential biomarkers for effective screening of neonatal sepsis infections: An overview

Neonatal sepsis, a clinical disorder developed by bacterial blood stream infections (BSI) in neonates, is one of the serious global public health problems that must be addressed. More than one million of the estimated global newborn deaths per year are occurred due to severe infections. The genesis of the infection is divided into early-onset sepsis (EOS) and late-onset sepsis (LOS) of the disease. The clinical complications of neonatal sepsis may be associated with bronchopulmonary dysplasia, ductus arteriosus and necrotizing enterocolitis. The clinical diagnosis and treatment of neonatal sepsis is highly complicated. Over the past few years distinct biomarkers have been identified. Most widely used biomarkers are C-reactive protein, Procalcitonin (PCT) and Serum amyloid A (SAA). Until recently, many potential biomarkers including Cell Surface antigens and Bacterial surface antigens and genetic biomarkers are being investigated. Protein biomarkers, cytokines and chemokines are getting much interest for identification of neonatal sepsis infection.

Preferential expression of IGHV and IGHD encoding antibodies with exceptionally long CDR3H and a rapid global shift in transcriptome characterizes development of bovine neonatal immunity

With an objective to understand natural development of bovine neonatal immunity, we analyzed 18 RNA-seq libraries from peripheral blood lymphocytes of three neonatal calves pre- (day 0) and post-colostrum (7, 14 and 28) uptake as compared to their dams. A significant global shift in neonatal transcriptome occurs within first week post-birth, in contrast to dams, with an upregulation of 717 genes. Global pathway analysis of the transcriptome revealed 110 differentially expressed immune-related genes, such as, complement, MHCII, chemokine receptors, defensins and cytokines, at birth. The signaling molecules (LAX1, BLK) and transcription factors (GATA3, FOXP3) are expressed at high levels. High expression of GATA3 transcription factor at birth seems to skew the neonatal immune response towards TH2 type. The high levels of T-cell signaling molecules, CD3G and CD3D, at birth are important in neonatal T cell development. Unlike adults, IGKC expression is high in the neonates where IGKV12 is preferentially expressed at birth. But IGLC is predominant in both neonates and adult where IGLV3.4 is preferentially expressed in B cells at birth. Both IGHM and IGHD are expressed at birth and IGHM achieves adult levels by day 7. This is followed by IGHA and IGHG expression 14-28 days post-birth. Importantly, preferential expression of IGHV1S1(BF4E9) and longest IGHD2(D_H2) genes that encode immunoglobulin with exceptionally long CDR3H at birth indicates their critical role, as B cell antigen receptor, in the B cell development via idiotype-anti-idiotype interactions. The transcriptome signatures described here permit assessment bovine neonatal immunocompetence. Bovine neonates acquire innate and IgM-mediated humoral immunocompetence within first week post-birth.

Passive acquisition of anti-Staphylococcus aureus antibodies by newborns via transplacental transfer and breastfeeding, regardless of maternal colonization

OBJECTIVE:

To investigate the transmission of anti-Staphylococcus aureus (Sa) IgG, IgG1 and IgG2 via placental transfer and the transfer of IgA via the colostrum according to maternal Sa carrier status at delivery.

METHODS:

We evaluated anti-Sa IgG, IgG1 and IgG2 in maternal and cord sera and IgA in colostrum from a case (n=49, Sa+) and a control group (n=98, Sa-).

RESULTS:

Of the 250 parturients analyzed for this study, 49 were nasally colonized with S. aureus (prevalence of 19.6%). Ninety-eight non-colonized subjects were selected for the control group. The anti-Sa IgG, IgG1 and IgG2 levels and the IgG avidity indexes in the maternal and cord sera did not differ between the groups, with a low transfer ratio of anti-Sa IgG to the newborns in both groups. The anti-Sa IgG2 titers were significantly higher than the IgG1 titers in the maternal and cord sera. Inversely, the transfer ratios were higher for anti-Sa IgG1 compared with IgG2; however, no differences between the groups were detected. The Sa-specific IgA levels and avidity indexes in the colostrum were equivalent between groups.

CONCLUSIONS:

Maternal Sa nasal colonization at delivery is not associated with higher antibody levels in the mother or newborns. The high titers of anti-Sa IgG2 found in the cord serum indicate a greater reactivity with non-protein antigens, which may further contribute to the susceptibility to staphylococcal infections at birth. The presence of IgA in the colostrum with avidity to S. aureus reinforces the importance of breastfeeding shortly after birth.

Functional Immune Cell Differences Associated With Low Vaccine Responses in Infants

BACKGROUND

We sought to understand why some children respond poorly to vaccinations in the first year of life.

METHODS

A total of 499 children (6-36 months old) provided serum and peripheral blood mononuclear cell samples after their primary and booster vaccination. Vaccine antigen-specific antibody levels were analyzed with enzyme-linked immunosorbent assay, and frequency of memory B cells, functional T-cell responses, and antigen-presenting cell responses were assessed in peripheral blood mononuclear cell samples with flow cytometric analysis.

RESULTS

Eleven percent of children were low vaccine responders, defined a priori as those with subprotective immunoglobulin G antibody levels to ≥66% of vaccines tested. Low vaccine responders generated fewer memory B cells, had reduced activation by CD4(+) and CD8(+) T cells on polyclonal stimulation, and displayed lower major histocompatibility complex II expression by antigen-presenting cells.

CONCLUSIONS

We conclude that subprotective vaccine responses in infants are associated with a distinct immunologic profile.

Neonatal Vaccination: Challenges and Intervention Strategies

BACKGROUND

While vaccines have been tremendously successful in reducing the incidence of serious infectious diseases, newborns remain particularly vulnerable in the first few months of their life to life-threatening infections. A number of challenges exist to neonatal vaccination. However, recent advances in the understanding of neonatal immunology offer insights to overcome many of those challenges.

OBJECTIVE

This review will present an overview of the features of neonatal immunity which make vaccination difficult, survey the mechanisms of action of available vaccine adjuvants with respect to the unique features of neonatal immunity, and propose a possible mechanism contributing to the inability of neonates to generate protective immune responses to vaccines.

METHODS

We surveyed recent published findings on the challenges to neonatal vaccination and possible intervention strategies including the use of novel vaccine adjuvants to develop efficacious neonatal vaccines.

RESULTS

Challenges in the vaccination of neonates include interference from maternal antibody and excessive skewing towards Th2 immunity, which can be counteracted by the use of proper adjuvants.

CONCLUSION

Synergistic stimulation of multiple Toll-like receptors by incorporating well-defined agonist-adjuvant combinations to vaccines is a promising strategy to ensure a protective vaccine response in neonates.

Staphylococcus epidermidis Bacteremia Induces Brain Injury in Neonatal Mice via Toll-like Receptor 2-Dependent and -Independent Pathways

BACKGROUND

Staphylococcus epidermidis causes late-onset sepsis in preterm infants. Staphylococcus epidermidis activates host responses in part via Toll-like receptor 2 (TLR2). Epidemiologic studies link bacteremia and neonatal brain injury, but direct evidence is lacking.

METHODS

Wild-type and TLR2-deficient (TLR2-/-) mice were injected intravenously with S. epidermidis at postnatal day 1 prior to measuring plasma and brain cytokine and chemokine levels, bacterial clearance, brain caspase-3 activation, white/gray matter volume, and innate transcriptome.

RESULTS

Staphylococcus epidermidis bacteremia spontaneously resolved over 24 hours without detectable bacteria in the cerebrospinal fluid (CSF). TLR2-/- mice demonstrated delayed S. epidermidis clearance from blood, spleen, and liver. Staphylococcus epidermidis increased the white blood cell count in the CSF, increased interleukin 6, interleukin 12p40, CCL2, and CXCL1 concentrations in plasma; increased the CCL2 concentration in the brain; and caused rapid (within 6 hours) TLR2-dependent brain activation of caspase-3 and TLR2-independent white matter injury.

CONCLUSIONS

Staphylococcus epidermidis bacteremia, in the absence of bacterial entry into the CSF, impairs neonatal brain development. Staphylococcus epidermidis bacteremia induced both TLR2-dependent and -independent brain injury, with the latter occurring in the absence of TLR2, a condition associated with an increased bacterial burden. Our study indicates that the consequences of transient bacteremia in early life may be more severe than commonly appreciated, and our findings may inform novel approaches to reduce bacteremia-associated brain injury.

Therapeutic utility of antibacterial peptides in wound healing

Cationic antimicrobial peptides were first thought to fight infection in animal models by disintegrating bacterial peptides and later by inhibiting bacteria-specific intracellular processes. However, ever increasing evidences indicate that cationic peptides accumulate around and modulate the immune system both systemically and in cutaneous and mucosal surfaces where injuries and infections occur. Native and designer antibacterial peptides as well as cationic peptides, never considered as antibiotics, promote wound healing at every step of cutaneous tissue regeneration. This article provides an introductory list of examples of how cationic peptides are involved in immunostimulation and epithelial tissue repair, eliminating wound infections and promoting wound healing in potential therapeutic utility in sight. Although a few antimicrobial peptides reached the Phase II clinical trial stage, toxicity concerns limit the potential administration routes. Resistance induction to both microbiology actions and the integrity of the innate immune system has to be carefully monitored.

Anti-lipoteichoic acid monoclonal antibody (pagibaximab) studies for the prevention of staphylococcal bloodstream infections in preterm infants

INTRODUCTION

Advances in modern medicine have given very low birth weight (VLBW) infants a better chance of survival; however, these infants remain at high risk for developing nosocomial infections associated with increased morbidity and mortality. The ability of antistaphylococcal immunoglobulins, Altastaph and INH A-2, to augment the neonatal immune system to prevent infections has been studied and evaluated in a 2009 Cochrane review.

AREAS COVERED

Our objective is to evaluate the safety and efficacy of a third antistaphylococcal immunoglobulin, pagibaximab, in the prevention of staphylococcal infection in preterm infants. Three studies of pagibaximab, Phases I, II and III, were examined in terms of study design, pharmacokinetics, development of sepsis and adverse effects.

EXPERT OPINION

These studies demonstrated safety and tolerability of pagibaximab with no observed reduction in sepsis. Reported adverse events in both treatment and placebo groups were similar and consistent with events commonly observed in VLBW infants. Antistaphylococcal immunoglobulins alone have been unsuccessful in preventing nosocomial infections. Further investigations need to evaluate any potential immunomodulating products in preterm animal models prior to human studies. Future studies are required to determine how to best augment the immature immune system, likely through the use of multiple immunomodulating agents to successfully prevent infections in preterm infants.

Development and maturation of the immune system in preterm neonates: results from a whole genome expression study

To expand the knowledge about the consecutive expression of genes involved in the immune system development in preterm neonates and to verify if the environment changes the gene expression after birth we conducted a prospective study that included three cohorts: (A) extremely (gestational age (GA): 23-26 weeks; n = 41), (B) very (GA: 27-29 weeks; n = 39), and (C) moderately preterm infants (GA: 30-32 weeks; n = 33). Blood samples were drawn from the study participants on the 5th and 28th day of life (DOL). The mRNA samples were evaluated for gene expression with the use of GeneChip Human Gene 1.0ST microarrays. Differential expression analysis revealed small subsets of genes that presented positive or negative monotone trends in both the 5th (138 genes) and 28th DOL (308 genes) in the three subgroups of patients. Based on pathway enrichment analysis, we found that most of the pathways that revealed a positive monotone trend were involved in host immunity. The most significantly GA dependent pathways were T-cell receptor signaling pathway and intestinal immune network for IgA production. Overall 4431 genes were differentially expressed between the 5th and 28th DOL. Despite differences in gestational age, patients with the same postconceptional age have a very similar expression of genes.