Evaluation of serotypes 5 and 8 capsular polysaccharides in protection against Staphylococcus aureus in murine models of infection

Glycoconjugate vaccines against antimicrobial resistant pathogens

INTRODUCTION

Antimicrobial resistance (AMR) is responsible for the death of millions worldwide and stands as a major threat to our healthcare systems, which are heavily reliant on antibiotics to fight bacterial infections. The development of vaccines against the main pathogens involved is urgently required as prevention remains essential against the rise of AMR.

AREAS COVERED

A systematic research review was conducted on MEDLINE database focusing on the six AMR pathogens defined as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli), which are considered critical or high priority pathogens by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC). The analysis was intersecated with the terms carbohydrate, glycoconjugate, bioconjugate, glyconanoparticle, and multiple presenting antigen system vaccines.

EXPERT OPINION

Glycoconjugate vaccines have been successful in preventing meningitis and pneumoniae, and there are high expectations that they will play a key role in fighting AMR. We herein discuss the recent technological, preclinical, and clinical advances, as well as the challenges associated with the development of carbohydrate-based vaccines against leading AMR bacteria, with focus on the ESKAPE pathogens. The need of innovative clinical and regulatory approaches to tackle these targets is also highlighted.

Protective efficacy of Alum adjuvanted Amidase protein vaccine against Staphylococcus aureus infection in multiple mouse models

AIMS

Staphylococcus aureus is an opportunistic pathogen of humans. No commercial vaccine is available to combat S. aureus infections. In this study, we have investigated the protective immune response generated by S. aureus non-covalently associated cell wall surface protein N-acetylmuramoyl-L-alanine amidase (AM) in combination with Alum (Al) and heat-killed S. aureus (hkSA) using murine models.

METHODS AND RESULTS

BALB/c mice were immunized with increasing concentrations of AM antigen or hkSA to determine their optimum concentration for vaccination. Fifty micrograms of AM and hkSA each were found to generate maximum anti-AM IgG antibody production. BALB/c mice were immunized next with 50 µg of AM, 50 µg of hKSA and 1 mg Al vaccine formulation. Vaccine efficacy was validated by challenging immunized BALB/c mice with S. aureus Newman and three clinical methicillin-resistant S. aureus strains. AM-hkSA-Al-immunized mice generated high anti-AM IgG antibody response with IgG1 and IgG2b as the predominant immunoglobulin subtypes. Increased survival (60%-90%) with decreased clinical disease symptoms was observed in the vaccinated BALB/c mice group. A significantly lower bacterial load and decreased kidney abscess formation was observed following the challenge with S. aureus in the vaccinated BALB/c mice group. Furthermore, the efficacy of AM-hkSA-Al vaccine was also validated using C57 BL/6 and Swiss albino mice.

CONCLUSIONS

Using murine infection models, we have demonstrated that AM-hkSA-Al vaccine would be effective in preventing S. aureus infections.

SIGNIFICANCE AND IMPACT OF STUDY

AM-hkSA-Al vaccine elicited strong immune response and may be considered for future vaccine design against S. aureus infections.

The Role of Bifidobacteria in Predictive and Preventive Medicine: A Focus on Eczema and Hypercholesterolemia

Bifidobacteria colonize the human gastrointestinal tract early on in life, their interaction with the host starting soon after birth. The health benefits are strain specific and could be due to the produced polysaccharides. The consumption of probiotics may prevent obesity, irritable bowel syndrome, eczema or atopic dermatitis, and asthma. Non-replicative strains of Bifidobacterium longum (NCC3001 and NCC2705) promote the differentiation of normal human epidermal keratinocytes (NHEKs), inducing a high expression of differentiation markers (keratin —KRT1—, and transglutaminase —TGM1—) and pro-regeneration markers (cathepsins), including β-defensin-1, which plays an important role in modulating the cutaneous immune response. Strains belonging to the genera Bifidobacterium and Lactobacillus can increase tight-junction proteins in NHEKs and enhance barrier function. Bifidobacteria and lactobacilli may be used as prophylactic or therapeutic agents towards enteric pathogens, antibiotic-associated diarrhea, lactose intolerance, ulcerative colitis, irritable bowel syndrome, colorectal cancer, cholesterol reduction, and control of obesity and metabolic disorders. Bifidobacterium bifidum showed an in vitro capability of lowering cholesterol levels thanks to its absorption into the bacterial membrane. Several strains of the species Lactobacillus acidophilus, L. delbrueckii subsp. bulgaricus, L. casei, and L. gasseri led to a reduced amount of serum cholesterol due to their ability to assimilate cholesterol (in vitro). Lactococcus lactis KF147 and Lactobacillus plantarum Lp81 have also been shown to reduce cholesterol levels by 12%. Clarifying the specific health mechanisms of Bifidobacterium and Lactobacillus strains in preventing high-cost pathologies could be useful for delineating effective guidelines for the treatment of infants and adults.

Immunofluorescence Microscopy for the Detection of Surface Antigens in Methicillin Resistant Staphylococcus aureus (MRSA)

Immunofluorescence microscopy is a widely used laboratory method which allows detection and visualization of specific antigens. The method employs the specificity of antibodies to deliver fluorophore to a specific target and then visualize it with a microscope. The power of the technique is that it requires relatively little manipulation and relatively few bacterial cells, enabling the detection of antigen expression where other methods cannot, such as during an actual infection in an animal. Here, we apply the method to follow antigen expression on the surface of MRSA cells over time in in vivo infection models.

Structural and immunological characterization of E. coli derived recombinant CRM197 protein used as carrier in conjugate vaccines

It is established that the immunogenicity of polysaccharides is enhanced by coupling them to carrier proteins. Cross reacting material (CRM₁₉₇), a nontoxic variant of diphtheria toxin (DT) is widely used carrier protein for polysaccharide conjugate vaccines. Conventionally, CRM₁₉₇ is isolated by fermentation of Corynebacterium diphtheriae C7 (β₁₉₇) cultures, which often suffers from low yield. Recently, several recombinant approaches have been reported with robust processes and higher yields, which will improve the affordability of CRM₁₉₇-based vaccines. Vaccine manufacturers require detailed analytical information to ensure that the CRM₁₉₇ meets quality standards and regulatory requirements. In the present manuscript we have described detailed structural characteristics of Escherichia coli based recombinant CRM₁₉₇ (rCRM₁₉₇) carrier protein. The crystal structure of the E. coli based rCRM₁₉₇ was found to be identical with the reported crystal structure of the C7 CRM₁₉₇ produced in C. diphtheriae C7 strain (Protein Data Bank (PDB) ID: 4EA0)_. The crystal structure of rCRM₁₉₇ was determined at 2.3 Å resolution and structure was submitted to the PDB with accession number ID 5I82. This is the first report of a crystal structure of E. coli derived recombinant CRM₁₉₇ carrier protein. Furthermore, the rCRM₁₉₇ was conjugated to Vi polysaccharide to generate Typhoid conjugate vaccine (Vi-rCRM₁₉₇) and its immunogenicity was evaluated in Balb/C Mice. The Vi-rCRM₁₉₇ conjugate vaccine was found to generate strong primary α-Vi antibody response and also showed a booster response after subsequent vaccination in mice. Overall data suggest that E. coli based recombinant CRM₁₉₇ exhibits structural and immunological similarity with the C7 CRM₁₉₇ and can be used as a carrier protein in conjugate vaccine development.

Murine Oropharyngeal Aspiration Model of Ventilator-associated and Hospital-acquired Bacterial Pneumonia

Murine infection models are critical for understanding disease pathogenesis and testing the efficacy of novel therapeutics designed to combat causative pathogens. Infectious pneumonia is among the most common infections presented by patients in the clinic and thus warrants an appropriate in vivo model. Typical pneumonia models use intranasal inoculation, which deposits excessive organisms outside the lung, causing off-target complications and symptoms, such as sinusitis, gastritis, enteritis, physical trauma, or microparticle misting to mimic aerosol spread more typical of viral, tuberculous, or fungal pneumonia. These models do not accurately reflect the pathogenesis of typical community- or healthcare-acquired bacterial pneumonia. In contrast, this murine model of oropharyngeal aspiration pneumonia mimics the droplet route in healthcare-acquired pneumonia. Inoculating 50 µL of the bacteria suspension into the oropharynx of anesthetized mice causes reflexive aspiration, which results in pneumonia. With this model, one can examine the pathogenesis of pneumonia-causing pathogens and new treatments to combat these diseases.

Skin microbiota-host interactions

The skin is a complex and dynamic ecosystem that is inhabited by bacteria, archaea, fungi and viruses. These microbes-collectively referred to as the skin microbiota-are fundamental to skin physiology and immunity. Interactions between skin microbes and the host can fall anywhere along the continuum between mutualism and pathogenicity. In this Review, we highlight how host-microbe interactions depend heavily on context, including the state of immune activation, host genetic predisposition, barrier status, microbe localization, and microbe-microbe interactions. We focus on how context shapes the complex dialogue between skin microbes and the host, and the consequences of this dialogue for health and disease.