Vaccines for Healthcare-associated Infections: Promise and Challenge

Clostridioides difficile infection: history, epidemiology, risk factors, prevention, clinical manifestations, treatment, and future options

SUMMARYClostridioides difficile infection (CDI) is one of the major issues in nosocomial infections. This bacterium is constantly evolving and poses complex challenges for clinicians, often encountered in real-life scenarios. In the face of CDI, we are increasingly equipped with new therapeutic strategies, such as monoclonal antibodies and live biotherapeutic products, which need to be thoroughly understood to fully harness their benefits. Moreover, interesting options are currently under study for the future, including bacteriophages, vaccines, and antibiotic inhibitors. Surveillance and prevention strategies continue to play a pivotal role in limiting the spread of the infection. In this review, we aim to provide the reader with a comprehensive overview of epidemiological aspects, predisposing factors, clinical manifestations, diagnostic tools, and current and future prophylactic and therapeutic options for C. difficile infection.

Exploring the Toxin-Mediated Mechanisms in Clostridioides difficile Infection

Clostridioides difficile infection (CDI) is the leading cause of nosocomial antibiotic-associated diarrhea, and colitis, with increasing incidence and healthcare costs. Its pathogenesis is primarily driven by toxins produced by the bacterium C. difficile, Toxin A (TcdA) and Toxin B (TcdB). Certain strains produce an additional toxin, the C. difficile transferase (CDT), which further enhances the virulence and pathogenicity of C. difficile. These toxins disrupt colonic epithelial barrier integrity, and induce inflammation and cellular damage, leading to CDI symptoms. Significant progress has been made in the past decade in elucidating the molecular mechanisms of TcdA, TcdB, and CDT, which provide insights into the management of CDI and the future development of novel treatment strategies based on anti-toxin therapies. While antibiotics are common treatments, high recurrence rates necessitate alternative therapies. Bezlotoxumab, targeting TcdB, is the only available anti-toxin, yet limitations persist, prompting ongoing research. This review highlights the current knowledge of the structure and mechanism of action of C. difficile toxins and their role in disease. By comprehensively describing the toxin-mediated mechanisms, this review provides insights for the future development of novel treatment strategies and the management of CDI.

Yinhuapinggan granule ameliorates lung injury caused by multidrug-resistant Acinetobacter baumannii via inhibiting NF-κB/NLRP3 pathway

Yinhuapinggan granule (YHPG) is a traditional Chinese medicine prescription with rich clinical experience for the treatment of colds and coughs. The aim of this study is to investigate the protective effect of YHPG on multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) infection in vivo and its potential anti-inflammatory mechanism. BALB/c mice were intranasally inoculated with MDR A. baumannii strain to establish the pneumonia infection model, and received intraperitoneally cyclophosphamide to form immunosuppression before attack. YHPG (6, 12 and 18 g/kg) was administered by gavage once a day for 3 consecutive days after infection. The protective effect of YHPG was evaluated by lung index, spleen index, thymus index, pathological changes of lung tissue and inflammatory factors (IL-1β, IL-6 and TNF-α) in serum. The expression of key targets of NF-κB/NLRP3 signaling pathway in vivo was analyzed by immunohistochemistry, immunofluorescence, reverse transcription quantitative PCR (RT-qPCR) and Western blot. The results showed that YHPG improved the lung index and its inhibition rate, immune organ indexes and lung pathological changes in infected mice, and significantly reduced IL-1β, IL-6 and TNF-α levels in serum. In addition, YHPG significantly down-regulated the mRNA and protein expression of NF-κB p65, NLRP3, ASC, Caspase-1, TNF-α, IL-6 and IL-1β in mice lung tissue. The results of the current study demonstrated that YHPG has significant protective effects on mice infected with MDR A.baumannii, which may be related to the regulation of inflammatory factors and NF-κB/NLRP3 signaling pathway, indicating that YHPG has a wide range of clinical application value and provides a theoretical basis for its treatment of MDR A.baumannii infection.

MicroRNA therapeutics and nucleic acid nano-delivery systems in bacterial infection: a review

Bacteria that have worked with humans for thousands of years pose a major threat to human health even today, as drug resistance has become a prominent problem. Compared to conventional drug therapy, nucleic acid-based therapies are a promising and potential therapeutic strategy for diseases in which nucleic acids are delivered through a nucleic acid delivery system to regulate gene expression in specific cells, offering the possibility of curing intractable diseases that are difficult to treat at this stage. Among the many nucleic acid therapeutic ideas, microRNA, a class of small nucleic acids with special properties, has made great strides in biology and medicine in just over two decades, showing promise in preclinical drug development. In this review, we introduce recent advances in nucleic acid delivery systems and their clinical applications, highlighting the potential of nucleic acid therapies, especially miRNAs extracted from traditional herbs, in combination with the existing set of nucleic acid therapeutic systems, to potentially open up a new line of thought in the treatment of cancer, viruses, and especially bacterial infectious diseases.

Innovation for infection prevention and control-revisiting Pasteur's vision

Louis Pasteur has long been heralded as one of the fathers of microbiology and immunology. Less known is Pasteur's vision on infection prevention and control (IPC) that drove current infection control, public health, and much of modern medicine and surgery. In this Review, we revisited Pasteur's pioneering works to assess progress and challenges in the process and technological innovation of IPC. We focused on Pasteur's far-sighted conceptualisation of the hospital as a reservoir of microorganisms and amplifier of transmission, aseptic technique in surgery, public health education, interdisciplinary working, and the protection of health services and patients. Examples from across the globe help inform future thinking for IPC innovation, adoption, scale up and sustained use.

Vaccines for healthcare associated infections without vaccine prevention to date

In spite of the widespread implementation of preventive strategies, the prevalence of healthcare-associated infections (HAIs) remains high. The prevalence of multidrug resistant organisms is high in HAIs. In 2019, the World Health Organization retained antimicrobial resistance as one of the ten issues for global health. The development of vaccines may contribute to the fight against antimicrobial resistance to reduce the burden of HAIs. Staphylococcus aureus, Gram negative bacteria and Clostridium difficile are the most frequent pathogens reported in HAIs. Consequently, the development of vaccines against these pathogens is crucial. At this stage, the goal of obtaining effective vaccines against S.aureus and Gram negative bacteria has not yet been achieved. However, we can expect in the near future availability of a vaccine against C. difficile. In addition, identifying populations who may benefit from these vaccines is complex, as at-risk patients are not great responders to vaccines, or as vaccination may occur too late, when they are already confronted to the risk. Vaccinating healthcare workers (HCWs) against these pathogens may have an impact only if HCWs play a role in the transmission and in the pathogens acquisition in patients, if the vaccine is effective to reduce pathogens carriage and if vaccine coverage is sufficient to protect patients. Acceptance of these potential vaccines should be evaluated and addressed in patients and in HCWs.

Challenges for Clinical Development of Vaccines for Prevention of Hospital-Acquired Bacterial Infections

Increasing antibiotic resistance in bacteria causing endogenous infections has entailed a need for innovative approaches to therapy and prophylaxis of these infections and raised a new interest in vaccines for prevention of colonization and infection by typically antibiotic resistant pathogens. Nevertheless, there has been a long history of failures in late stage clinical development of this type of vaccines, which remains not fully understood. This article provides an overview on present and past vaccine developments targeting nosocomial bacterial pathogens; it further highlights the specific challenges associated with demonstrating clinical efficacy of these vaccines and the facts to be considered in future study designs. Notably, these vaccines are mainly applied to subjects with preexistent immunity to the target pathogen, transient or chronic immunosuppression and ill-defined microbiome status. Unpredictable attack rates and changing epidemiology as well as highly variable genetic and immunological strain characteristics complicate the development. In views of the clinical need, re-thinking of the study designs and expectations seems warranted: first of all, vaccine development needs to be footed on a clear rationale for choosing the immunological mechanism of action and the optimal time point for vaccination, e.g., (1) prevention (or reduction) of colonization vs. prevention of infection and (2) boosting of a preexistent immune response vs. altering the quality of the immune response. Furthermore, there are different, probably redundant, immunological and microbiological defense mechanisms that provide protection from infection. Their interplay is not well-understood but as a consequence their effect might superimpose vaccine-mediated resolution of infection and lead to failure to demonstrate efficacy. This implies that improved characterization of patient subpopulations within the trial population should be obtained by pro- and retrospective analyses of trial data on subject level. Statistical and systems biology approaches could help to define immune and microbiological biomarkers that discern populations that benefit from vaccination from those where vaccines might not be effective.

Clostridium difficile-associated disease and Helicobacter pylori seroprevalence: A case-control study

BACKGROUND

Helicobacter pylori inhabits the stomach and causes persistent inflammation, with changes in gastric acidity. However, it is unclear whether the presence of H pylori plays a role in Clostridium difficile-associated disease (CDAD). The study's aim was to examine relationships of H pylori seroprevalence and serum pepsinogens (PGs), as markers of gastric inflammation, with CDAD.

MATERIALS AND METHODS

A case-control study was conducted among 49 CDAD cases and 54 controls (median age 82 years). Using enzyme-linked immunosorbent assays, sera were tested for H pylori IgG antibody, and PGI and PGII levels. Helicobacter pylori-positive samples were tested for IgG antibody to recombinant cytotoxin-associated gene A (CagA) virulent protein. Logistic regression models were fitted.

RESULTS

Cases and controls were comparable in age (P = .5) and sex distribution (females 62% vs 57%, P = .6). Helicobacter pylori IgG seroprevalence was 47%, of whom 23% were CagA seropositives. Among cases compared to controls, 43% vs 28% were H pylori seropositive but lacking CagA IgG antibody: adjusted odd ratio (OR) 3.43 (95% confidence intervals [CI] 1.29-9.10); 18% vs 4% were positive for CagA phenotype: adjusted OR 9.32 (95% CI 1.61-53.76). This association was not affected by PG levels.

CONCLUSIONS

Helicobacter pylori infection, especially with CagA virulent phenotype, might predispose to C difficile infection in elderly patients.

Microbiome as a tool and a target in the effort to address antimicrobial resistance

Reciprocal, intimate relationships between the human microbiome and the host immune system are shaped by past microbial encounters and prepare the host for future ones. Antibiotics and other antimicrobials leave their mark on both the microbiome and host immunity. Antimicrobials alter the structure of the microbiota, expand the host-specific pool of antimicrobial-resistance genes and organisms, degrade the protective effects of the microbiota against invasion by pathogens, and may impair vaccine efficacy. Through these effects on the microbiome they may affect immune responses. Vaccines that exert protective or therapeutic effects against pathogens may reduce the use of antimicrobials, the development and spread of antimicrobial resistance, and the harmful impacts of these drugs on the microbiome. Other strategies involving manipulation of the microbiome to deplete antibiotic-resistant organisms or to enhance immune responses to vaccines may prove valuable in addressing antimicrobial resistance as well. This article describes the intersections of immunity, microbiome and antimicrobial exposure, and the use of vaccines and other alternative strategies for the control and management of antimicrobial resistance.

Prevalence of IgG and Neutralizing Antibodies against Staphylococcus aureus Alpha-Toxin in Healthy Human Subjects and Diverse Patient Populations

Staphylococcus aureus causes an array of serious infections resulting in high morbidity and mortality worldwide. This study evaluated naturally occurring serum anti-alpha-toxin (anti-AT) antibody levels in human subjects from various age groups, individuals with S. aureus dialysis and surgical-site infections, and S. aureus-colonized versus noncolonized subjects. Anti-AT immunoglobulin G (IgG) and neutralizing antibody (NAb) levels in infants (aged ≤1 year) were significantly lower than those in other populations. In comparison to adolescent, adult, and elderly populations, young children (aged 2 to 10 years) had equivalent anti-AT IgG levels but significantly lower anti-AT NAb levels. Therefore, the development of anti-AT NAbs appears to occur later than that of AT-specific IgG, suggesting a maturation of the immune response to AT. Anti-AT IgG levels were slightly higher in S. aureus-colonized subjects than in noncolonized subjects. The methicillin susceptibility status of colonizing isolates had no effect on anti-AT antibody levels in S. aureus-colonized subjects. The highest anti-AT IgG and NAb levels were observed in dialysis patients with acute S. aureus infection. Anti-AT IgG and NAb levels were well correlated in subjects aged >10 years, regardless of colonization or infection status. These data demonstrate that AT elicits a robust IgG humoral response in infants and young children that becomes stable prior to adolescence, matures into higher levels of NAbs in healthy adolescents, and becomes elevated during S. aureus infection. These findings may assist in identifying subjects and patient populations that could benefit from vaccination or immunoprophylaxis with anti-AT monoclonal antibodies.

Immune response effects of diverse vaccine antigen attachment ways based on the self-made nanoemulsion adjuvant in systemic MRSA infection

Nanoemulsion adjuvants-based vaccines have potent induced immune responses against methicillin-resistant Staphylococcus aureus (MRSA) infection. However, the efficacies and immune responses of different antigen-attaching ways on self-made nanoemulsion adjuvants remain unknown. In this study, we designed three formulations of nanoemulsion adjuvants (encapsulation, mixture, and combination) to explore their immune response-enhancing effects and their underlying mechanism in a systemic infection model of MRSA. Our results showed that the three nanoemulsion-attachment ways formulated with a fusion antigen of MRSA (Hla_H35LIsdB_348–465) all improved humoral and cellular immune responses. When compared with the mixture and combination formulations, the nanoemulsion-encapsulation group effectively promoted the antigen uptake of dendritic cells (DCs) in vitro, the activation of DC in draining lymph nodes and the delayed release of antigen at injection sites in vivo. Moreover, the encapsulation group induced a more ideal protective efficacy in a MRSA sepsis model by inducing more potent antibody responses and a Th1/Th17 biased CD4⁺ T cell response when compared with the other two attachment ways. Our findings suggested that the encapsulated formulation of vaccine with nanoemulsion adjuvant is an effective attachment way to provide protective immunity against MRSA infection.

Encapsulated formulation of nanoemulsion vaccine induced more potent immune responses against methicillin-resistant Staphylococcus aureus (MRSA) infection, compared with combination and mixture attachment ways.

Les vaccins dans la prévention des infections associées aux soins

Les infections associées aux soins (IAS) constituent un véritable problème de santé publique. Escherichia coli, Staphylococcus aureus, Clostridium difficile sont les plus souvent à l’origine des IAS. L’antibiorésistance fréquente complique encore la prise en charge et des impasses thérapeutiques existent à présent. Les mesures d’hygiène hospitalière bien qu’essentielles sont insuffisantes pour diminuer drastiquement les IAS. Ainsi, des stratégies alternatives à l’antibiothérapie s’avèrent nécessaires pour prévenir et traiter les IAS. Parmi celles-ci, la vaccination et l’immunisation passive sont probablement les plus prometteuses. Nous avons fait une mise au point sur les vaccins disponibles et en développement clinique pour lutter contre les IAS, chez les patients à risque d’IAS et les soignants. L’intérêt de la vaccination grippale et rotavirus chez les patients pour prévenir ces IAS virales a été examiné. Le développement d’un vaccin anti-S. aureus, déjà émaillé de 2 échecs est complexe. Toutefois, ces échecs ont permis d’améliorer les connaissances sur l’immunité anti-S. aureus. La mise à disposition d’un vaccin préventif anti-C. difficile semble plus proche. Pour les autres bactéries gram négatif responsables d’IAS, le développement est moins avancé. La vaccination des patients à risques d’IAS pose également des problèmes de réponse vaccinale qu’il faudra résoudre pour utiliser cette stratégie. Ainsi, la vaccination des soignants, de par l’effet de groupe permet également de prévenir les IAS. Nous faisons ici le point sur l’intérêt de la vaccination des soignants contre la rougeole, la coqueluche, la grippe, la varicelle, l’hépatite B pour réduire les IAS avec des vaccins déjà disponibles.

The intensive care medicine research agenda on multidrug-resistant bacteria, antibiotics, and stewardship

PURPOSE

To concisely describe the current standards of care, major recent advances, common beliefs that have been contradicted by recent trials, areas of uncertainty, and clinical studies that need to be performed over the next decade and their expected outcomes with regard to the management of multidrug-resistant (MDR) bacteria, antibiotic use, and antimicrobial stewardship in the intensive care unit (ICU) setting.

METHODS

Narrative review based on a systematic analysis of the medical literature, national and international guidelines, and expert opinion.

RESULTS

The prevalence of infection of critically ill patients by MDR bacteria is rapidly evolving. Clinical studies aimed at improving understanding of the changing patterns of these infections in ICUs are urgently needed. Ideal antibiotic utilization is another area of uncertainty requiring additional investigations aimed at better understanding of dose optimization, duration of therapy, use of combination treatment, aerosolized antibiotics, and the integration of rapid diagnostics as a guide for treatment. Moreover, there is an imperative need to develop non-antibiotic approaches for the prevention and treatment of MDR infections in the ICU. Finally, clinical research aimed at demonstrating the beneficial impact of antimicrobial stewardship in the ICU setting is essential.

CONCLUSIONS

These and other fundamental questions need to be addressed over the next decade in order to better understand how to prevent, diagnose, and treat MDR bacterial infections. Clinical studies described in this research agenda provide a template and set priorities for investigations that should be performed in this field.

Design of live attenuated bacterial vaccines based on D-glutamate auxotrophy

Vaccine development is a priority for global health due to the growing multidrug resistance in bacteria. D-glutamate synthesis is essential for bacterial cell wall formation. Here we present a strategy for generating effective bacterial whole-cell vaccines auxotrophic for D-glutamate. We apply this strategy to generate D-glutamate auxotrophic vaccines for three major pathogens, Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus. These bacterial vaccines show virulence attenuation and self-limited growth in mice, and elicit functional and cross-reactive antibodies, and cellular immunity. These responses correlate with protection against acute lethal infection with other strains of the same species, including multidrug resistant, virulent and/or high-risk clones such as A. baumannii AbH12O-A2 and Ab307-0294, P. aeruginosa PA14, and community-acquired methicillin-resistant S. aureus USA300LAC. This approach can potentially be applied for the development of live-attenuated vaccines for virtually any other bacterial pathogens, and does not require the identification of virulence determinants, which are often pathogen-specific.

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SUMMARYThe explosion of vaccines during the 20th century allowed the control of numerous infectious plagues but multiple challenges oppose conservation and extension of these successes. The hesitation of modern societies in front of vaccinations requires researches in life, human and social sciences in order to reach a better understanding of vaccines mechanism of action and to improve the tolerance and acceptability of vaccines and additives. The ageing of the populations and the increase of subjects at risk also require to improve the immunogenicity and the efficiency of existing vaccines. The constant emergence of new epidemics or the development of the antibio-resistance imposes innovation and development of new vaccines. The recent difficulties faced by the development of vaccines against malaria, tuberculosis or AIDS illustrate the necessity of moving beyond classical recipes and of elaborating new vectors and new adjuvants, of better understanding the heterogeneity of vaccine immunity and of developing alternative routes of immunization. Multidisciplinary researches using the most recent advances in molecular, structural and cellular biology, in microbiology, immunology and of genetic engineering to answer these worldwide challenges.