Klebsiella pneumoniae is a major opportunistic pathogen, where the polysaccharide capsule is traditionally recognized as a critical virulence determinant. However, its role in surface interactions and intracellular adaptation remains incompletely understood. Here, we combined phenotypic assays with physicochemical analyses to dissect the contribution of the capsule. A wza knockout mutant displayed enhanced biofilm formation, adhesion, and invasion of epithelial cells compared to the encapsulated strain. Zeta potential and hydrodynamic size measurements revealed that capsule absence increased surface negativity and exposure of adhesion structures, thereby promoting host-cell interactions. In contrast, intracellular survival assays demonstrated that the capsule conferred a clear advantage for persistence and replication. Together, our results support a dynamic model in which capsule expression imposes a trade-off: restricting early adhesion and biofilm development but favoring long-term intracellular survival. This trade-off model expands the understanding of capsule biology and may inform novel strategies to disrupt colonization or persistence in antibiotic-resistant K. pneumoniae.

Streptococcus pneumoniae remains a leading cause of morbidity and mortality worldwide, with current polysaccharide-based vaccines offering limited serotype coverage, high production costs, and reduced efficacy in vulnerable populations. These limitations have prompted the search for conserved pneumococcal proteins as universal vaccine candidates. Among them, pneumococcal surface protein A (PspA) stands out as a major virulence factor, present in virtually all clinically relevant strains, and capable of interfering with complement activation, opsonophagocytosis, and host defense mechanisms. Over three decades of research have demonstrated PspA’s strong immunogenicity, protective efficacy in multiple animal models, and safety in early-phase clinical trials. Here, we critically review advances in PspA-based vaccine development, including recombinant protein fragments, fusion constructs, nanoparticle formulations, and live-vector platforms. We highlight the structural and immunological determinants underlying its protective potential, while discussing major challenges such as antigenic variability and cross-reactivity across pneumococcal strains expressing distinct PspA clades. By integrating recent experimental and translational findings, this review outlines the opportunities and obstacles for the implementation of serotype-independent PspA-based vaccines.

Background: Klebsiella pneumoniae infections pose a great burden worldwide, causing high morbidity and mortality, which are worsened by the increase in multidrug-resistant strains. New therapeutic/prophylactic strategies are urgently needed to overcome antibiotic resistance and reduce the health and economic impacts of diseases caused by this pathogen. Fimbriae are important virulence factors involved in biofilm formation and adhesion to host cells. Their exposed location, conservation among clinical isolates and adjuvant properties make them interesting candidates for inclusion in protein-based vaccines. Therefore, the present work investigated the immunological potential of type 1 and 3 fimbriae subunits in a murine model of K. pneumoniae lung infection. Methods: MrkA and FimA were produced as recombinant proteins in E. coli, purified and used to immunize mice subcutaneously. The immune responses were characterized and protection against pneumonia was evaluated after intranasal challenge. Results: Subcutaneous immunization with recombinant FimA and MrkA induced high IgG1 production; the antibodies efficiently recognized the native proteins at the bacterial surface, promoted C3 deposition and reduced biofilm formation by K. pneumoniae in vitro. Mice vaccinated with the co-administered proteins reduced the bacterial loads in the lungs after intranasal challenge, less inflammation and reduced tissue damage. Conclusion: The results suggest that both type 1 and type 3 fimbriae contribute to protection against K. pneumoniae lung infection, inducing antibodies that bind to the bacteria and favoring Complement deposition and clearance by the host, while inhibiting biofilm formation.

Klebsiella pneumoniae infections pose a great burden worldwide, causing high morbidity and mortality. New therapeutic/prophylactic strategies are urgently needed to overcome antibiotic resistance and reduce the health and economic impacts of diseases caused by this pathogen. Fimbriae are important virulence factors involved in biofilm formation and adhesion to host cells. Their exposed location and conservation among clinical isolates make them interesting candidates for inclusion in protein-based vaccines. Therefore, the present work investigated the immunological potential of K. pneumoniae fimbriae subunits as vaccine candidates. In-silico analysis of the type 1 (FimA and FimH) and type 3 (MrkA and MrkD) fimbrial components showed that all four proteins contain B- and T- cell epitopes predicted to bind into the peptide binding cleft. Additionally, a 7-allele prediction model was used to assess the binding and presentation of these epitopes, with some showing potential for presentation across different class II MHC alleles. The genes encoding fimbriae subunits FimA and MrkA were cloned in prokaryotic vector systems, expressed in E. coli and purified by Ni2+ affinity chromatography. Subcutaneous immunization of mice with recombinant FimA and MrkA using Alum as adjuvant induced specific IgG production. The protective potential of MrkA immunization was tested against challenge with a hypervirulent K. pneumoniae strain; although a modest increase in survival time was observed in the immunized group, all mice died within 5 days of infection. Overall, although the in-silico analysis suggests that K. pneumoniae fimbriae components promising vaccine candidates, protection against highly virulent strains with increased capsule may require additional antigens.

[This corrects the article DOI: 10.3389/fcimb.2022.877995.].

Acinetobacter baumannii is a Gram-negative bacterium considered an emerging multi-drug-resistant pathogen. Furthermore, this bacterium can survive in extreme environmental conditions, which makes it a frequent cause of nosocomial infection outbreaks. Gene expression analyses by Reverse Transcription Quantitative Real-Time PCR (RT-qPCR) depend on a reference gene, also called an endogenous gene, which is used to normalize the generated data and thus ensure an accurate analysis with minimal errors. Currently, gene expression analyses in A. baumannii are compromised, as there are no reports in the literature describing the identification of validated reference genes for use in RT-qPCR analyses. For this reason, we selected twelve candidate reference genes of A. baumannii and assessed their expression profile under different experimental and culture conditions. The expression stability of the candidate genes was evaluated by using statistical algorithms such as BestKeeper, GeNorm, NormFinder, Delta C T , and RefFinder, in order to identify the most suitable candidate reference genes for RT-qPCR analyses. The statistical analyses indicated rpoB , rpoD , and fabD genes as the most adequate to ensure accurate normalization of RT-qPCR data in A. baumannii . The accuracy of the proposed reference genes was validated by using them to normalize the expression of the ompA gene, encoding the outer membrane protein A, in A. baumannii sensible and resistant to the antibiotic polymyxin. The present work provides suitable reference genes for precise RT-qPCR data normalization on future gene expression studies with A. baumannii .

BACKGROUND:Klebsiella pneumoniae is a Gram-negative pathogen that has become a threat to public health worldwide due to the emergence of hypervirulent and multidrug-resistant strains. Cell-surface components, such as polysaccharide capsules, fimbriae, and lipopolysaccharides (LPS), are among the major virulence factors for K. pneumoniae. One of the genes involved in LPS biosynthesis is the uge gene, which encodes the uridine diphosphate galacturonate 4-epimerase enzyme. Although essential for the LPS formation in K. pneumoniae, little is known about the mechanisms that regulate the expression of uge. Ferric uptake regulator (Fur) is an iron-responsive transcription factor that modulates the expression of capsular and fimbrial genes, but its role in LPS expression has not yet been identified. This work aimed to investigate the role of the Fur regulator in the expression of the K. pneumoniae uge gene and to determine whether the production of LPS by K. pneumoniae is modulated by the iron levels available to the bacterium. RESULTS:Using bioinformatic analyses, a Fur-binding site was identified on the promoter region of the uge gene; this binding site was validated experimentally through Fur Titration Assay (FURTA) and DNA Electrophoretic Mobility Shift Assay (EMSA) techniques. RT-qPCR analyses were used to evaluate the expression of uge according to the iron levels available to the bacterium. The iron-rich condition led to a down-regulation of uge, while the iron-restricted condition resulted in up-regulation. In addition, LPS was extracted and quantified on K. pneumoniae cells subjected to iron-replete and iron-limited conditions. The iron-limited condition increased the amount of LPS produced by K. pneumoniae. Finally, the expression levels of uge and the amount of the LPS were evaluated on a K. pneumoniae strain mutant for the fur gene. Compared to the wild-type, the strain with the fur gene knocked out presented a lower LPS amount and an unchanged expression of uge, regardless of the iron levels. CONCLUSIONS:Here, we show that iron deprivation led the K. pneumoniae cells to produce higher amount of LPS and that the Fur regulator modulates the expression of uge, a gene essential for LPS biosynthesis. Thus, our results indicate that iron availability modulates the LPS biosynthesis in K. pneumoniae through a Fur-dependent mechanism.

Childhood respiratory diseases, such as asthma, are important public health problems worldwide and could be associated with tooth enamel defects. This study aimed to verify the relationship between asthma and enamel defects in teeth, to answer the following question: "Could asthma in children be significantly associated with enamel defects in deciduous dentition and young permanent teeth?." PUBMED-MEDLINE, EMBASE, LILACS, and COCHRANE databases were systematically searched and assessed articles (2000-2021) were cautiously scored according to a predetermined criterion. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses were considered. Twenty-two articles were critically appraised and used as a basis for conclusions. The relationship between asthma and enamel defects was confirmed in the majority of appraised papers, one with a high level of evidence, nine with a moderate level, and four with a low level. Out of the eight manuscripts investigating the influence of asthma medication on enamel defects, only three (one with high, one moderate, and another with a low level of evidence) suggested an association. It can be concluded that asthma is closely connected with enamel defects in young permanent teeth. However, as most of the papers appraised were of cross-sectional or case-control design, further well-designed clinical investigations with a prospective design are welcome to reinforce our findings.

Introdução: Acinetobacter baumannii é uma bactéria Gram-negativa, considerada um patógeno oportunista, e capaz de sobreviver em condições ambientais extremas, o que a torna uma causa frequente de surtos de infecção hospitalar, acarretando uma diversa gama de infecções. Devido a sua alta capacidade adaptativa, A. baumannii é extremamente resistente a antimicrobianos e desinfetantes, se espalhando facilmente entre pacientes mais vulneráveis, tendo maior incidência em UTIs. Objetivos: Este estudo teve o objetivo de investigar a incidência de infecções hospitalares por Acinetobacter baumannii devido à pandemia da COVID-19. Material e métodos: Para a realização deste estudo foi realizada uma revisão bibliográfica a partir de artigos científicos baseados nos principais bancos de dados, tais como Pubmed, Scielo e Lilacs. Para a busca de artigos utilizou-se os Descritores em Ciências da Saúde “Acinetobacter baumannii”, “COVID-19” e “Infecção Hospitalar”, priorizando os artigos publicados nos últimos dois anos. Resultados: Ao realizar a análise de dados dos artigos selecionados, verificou-se que houve um aumento no número de co-infecções por Acinetobacter baumannii em pacientes internados devido ao coronavírus Sars-CoV-2 em diversos países, intensificando a progressão e o prognóstico desses pacientes. A pandemia pelo COVID-19 levou a um aumento do número de pacientes em ventilação mecânica com consequente aumento das ocorrências de infecção por A. baumannii, assim como o uso indiscriminado de antibióticos propiciou a seleção de bactérias resistentes, elevando principalmente as taxas de resistência dos carbapenêmicos para A. baumannii e K. pneumoniae. Além disso, o potencial de propagação da infecção por A. baumannii aumentou à medida que os equipamentos de proteção (EPI”s), a contratação massiva de novos profissionais de UTI’s sem experiência, “práticas hospitalares padrão” (capacidade e recursos ideais) foram ficando escassos, devido à pandemia. Conclusão: Considerando que infecções bacterianas secundárias são consideradas fatores de risco para a gravidade e as taxas de mortalidade da Covid-19, práticas que visam o uso otimizado de antimicrobianos e a melhoria do controle de infecções são fundamentais para conter coinfecções de Sars-Cov-2 com bactérias.

PspA and pneumolysin are two important vaccine candidates, able to elicit protection in different models of pneumococcal infection. The high immunogenic potential of PspA, combined with a possible adjuvant effect of pneumolysin derivatives (due to their ability to interact with TLR-4) could greatly improve the immunogenicity and coverage of a protein-based pneumococcal vaccine. A chimeric protein including the N-terminal region of PspA in fusion with the pneumolysin derivative, PlD1, has been shown to induce high antibody levels against each protein, and protect mice against invasive challenge. The aim of the present study was to investigate the cellular response induced by such vaccine, and to evaluate protection in a murine model of lobar pneumococcal pneumonia. Pneumococcal pneumonia was induced in BALB/c mice by nasal instillation of a high dose of a serotype 14 strain with low virulence. Airway inflammation was confirmed by total and differential cell counts in BAL and by histological analysis of the lungs, and bacterial loads were measured 7 days after challenge. Cytokine levels were determined in the bronchoalveolar fluid (BALF) of mice immunized with rPspA-PlD1 fusion after challenge, by flow cytometry and ELISA. After challenge, the mice developed lung inflammation with no invasion of other sites, as demonstrated by histological analysis. We detected significant production of TNF-α and IL-6 in the BALF, which correlated with protection against pneumonia in the group immunized with rPspA-PlD1. In conclusion, we found that the rPspA-PlD1fusion is protective against pneumococcal pneumonia in mice, and protection is correlated with an early and controlled local inflammatory response. These results are in agreement with previous data demonstrating the efficacy of the fusion protein against pneumococcal sepsis and reinforce the potential of the rPspA-PlD1 protein chimera as a promising vaccine strategy to prevent pneumococcal disease.

Humans and food production animals have been reported to be important reservoirs of antimicrobial resistance (AMR) genes (ARGs). The frequency of these multidrug-resistant (MDR) bacteria tends to be higher in low- and middle-income countries (LMICs), due mainly to a lack of public health policies.

The ability to form biofilms is a crucial virulence trait for several microorganisms, including Klebsiella pneumoniae – a Gram-negative encapsulated bacterium often associated with nosocomial infections. It is estimated that 65-80% of bacterial infections are biofilm related. Biofilms are complex bacterial communities composed of one or more species encased in an extracellular matrix made of proteins, carbohydrates and genetic material derived from the bacteria themselves as well as from the host. Bacteria in the biofilm are shielded from immune responses and antibiotics. The present review discusses the characteristics of K. pneumoniae biofilms, factors affecting biofilm development, and their contribution to infections. We also explore different model systems designed to study biofilm formation in this species. A great number of factors contribute to biofilm establishment and maintenance in K. pneumoniae, which highlights the importance of this mechanism for the bacterial fitness. Some of these molecules could be used in future vaccines against this bacterium. However, there is still a lack of in vivo models to evaluate the contribution of biofilm development to disease pathogenesis. With that in mind, the combination of different methodologies has great potential to provide a more detailed scenario that more accurately reflects the steps and progression of natural infection.

The One Health concept is a global strategy to study the relationship between human and animal health and the transfer of pathogenic and non-pathogenic species between these systems. However, to the best of our knowledge, no data based on One Health genome-centric metagenomics are available in public repositories. Here, we present a dataset based on a pilot-study of 2,915 metagenome-assembled genomes (MAGs) of 107 samples from the human (N = 34), cattle (N = 28), swine (N = 15) and poultry (N = 30) gut microbiomes. Samples were collected from the five Brazilian geographical regions. Of the draft genomes, 1,273 were high-quality drafts (≥90% of completeness and ≤5% of contamination), and 1,642 were medium-quality drafts (≥50% of completeness and ≤10% of contamination). Taxonomic predictions were based on the alignment and concatenation of single-marker genes, and the most representative phyla were Bacteroidota, Firmicutes, and Proteobacteria. Many of these species represent potential pathogens that have already been described or potential new families, genera, and species with potential biotechnological applications. Analyses of this dataset will highlight discoveries about the ecology and functional role of pathogens and uncultivated Archaea and Bacteria from food-producing animals and humans. Furthermore, it also represents an opportunity to describe new species from underrepresented taxonomic groups.

Although originally known as an opportunistic pathogen, Klebsiella pneumoniae has been considered a worldwide health threat nowadays due to the emergence of hypervirulent and antibiotic-resistant strains capable of causing severe infections not only on immunocompromised patients but also on healthy individuals. Fimbriae is an essential virulence factor for K. pneumoniae, especially in urinary tract infections (UTIs), because it allows the pathogen to adhere and invade urothelial cells and to form biofilms on biotic and abiotic surfaces. The importance of fimbriae for K. pneumoniae pathogenicity is highlighted by the large number of fimbrial gene clusters on the bacterium genome, which requires a coordinated and finely adjusted system to control the synthesis of these structures. In this work, we describe KpfR as a new transcriptional repressor of fimbrial expression in K. pneumoniae and discuss its role in the bacterium pathogenicity. K. pneumoniae with disrupted kpfR gene exhibited a hyperfimbriated phenotype with enhanced biofilm formation and greater adhesion to and replication within epithelial host cells. Nonetheless, the mutant strain was attenuated for colonization of the bladder in a murine model of urinary tract infection. These results indicate that KpfR is an important transcriptional repressor that, by negatively controlling the expression of fimbriae, prevents K. pneumoniae from having a hyperfimbriated phenotype and from being recognized and eliminated by the host immune system.

The implementation of polysaccharide-based vaccines has massively reduced the incidence of invasive pneumococcal diseases. However, there is great concern regarding serotype replacement and the increase in antibiotic resistant strains expressing non-vaccine capsular types. In addition, conjugate vaccines have high production costs, a limiting factor for their implementation in mass immunization programs in developing countries. These limitations have prompted the development of novel vaccine strategies for prevention of Streptococcus pneumoniae infections. The use of conserved pneumococcal antigens such as recombinant proteins or protein fragments presents an interesting serotype-independent alternative. Pht is a family of surface-exposed proteins which have been evaluated as potential vaccine candidates with encouraging results. The present work investigated the immune responses elicited by subcutaneous immunization of mice with the polyhistidine triad protein D (PhtD) and its amino and carboxyl terminal fragments. The proteins were immunogenic and protective against pneumococcal sepsis in mice. Antibodies raised against PhtD increased complement C3b deposition on the pneumococcal surface, mainly mediated by the alternative pathway. Sera from mice immunized with PhtD and PhtD_Cter promoted an increase in bacterial uptake by mouse phagocytes. The interaction of PhtD with the complement system regulator factor H was investigated in silico and in vitro by ELISA and western blot, confirming PhtD as a factor-H binding protein. Our results support the inclusion of PhtD and more specifically, its C-terminal fragment in a multicomponent serotype independent vaccine and suggests a role for the complement system in PhtD-mediated protection.

Klebsiella pneumoniae is a Gram-negative pathogen that has become a worldwide concern due to the emergence of multidrug-resistant isolates responsible for various invasive infectious diseases. Biofilm formation constitutes a major virulence factor for K. pneumoniae and relies on the expression of fimbrial adhesins and aggregation of bacterial cells on biotic or abiotic surfaces in a coordinated manner. During biofilm aggregation, bacterial cells communicate with each other through inter- or intra-species interactions mediated by signallng molecules, called autoinducers, in a mechanism known as quorum sensing (QS). In most Gram-negative bacteria, intra-species communication typically involves the LuxI/LuxR system: LuxI synthase produces N -acyl homoserine lactones (AHLs) as autoinducers and the LuxR transcription factor is their cognate receptor. However, K. pneumoniae does not produce AHL but encodes SdiA, an orphan LuxR-type receptor that responds to exogenous AHL molecules produced by other bacterial species. While SdiA regulates several cellular processes and the expression of virulence factors in many pathogens, the role of this regulator in K. pneumoniae remains unknown. In this study, we describe the characterization of sdiA mutant strain of K. pneumoniae . The sdiA mutant strain has increased biofilm formation, which correlates with the increased expression of type 1 fimbriae, thus revealing a repressive role of SdiA in fimbriae expression and bacterial cell adherence and aggregation. On the other hand, SdiA acts as a transcriptional activator of cell division machinery assembly in the septum, since cells lacking SdiA regulator exhibited a filamentary shape rather than the typical rod shape. We also show that K. pneumoniae cells lacking SdiA regulator present constant production of QS autoinducers at maximum levels, suggesting a putative role for SdiA in the regulation of AI-2 production. Taken together, our results demonstrate that SdiA regulates cell division and the expression of virulence factors such as fimbriae expression, biofilm formation, and production of QS autoinducers in K. pneumoniae .

Excess caloric intake and body fat accumulation lead to obesity, a complex chronic disease that represents a significant public health problem due to the health-related risk factors. There is growing evidence showing that maternal obesity can program the offspring, which influences neonatal phenotype and predispose offspring to metabolic disorders such as obesity. This increased risk may also be epigenetically transmitted across generations. Thus, there is an imperative need to find effective reprogramming approaches in order to resume normal fetal development. Polyphenols are bioactive compounds found in vegetables and fruits that exert its anti-obesity effect through its powerful anti-oxidant and anti-inflammatory activities. Polyphenol supplementation has been proven to counteract the prejudicial effects of maternal obesity programming on progeny. Indeed, some polyphenols can cross the placenta and protect the fetal predisposition against obesity. The present review summarizes the effects of dietary polyphenols on obesity-induced maternal reprogramming as an offspring anti-obesity approach.

Despite the undeniable success of polysaccharide vaccines against Streptococcus pneumoniae infections, there is a consensus on the scientific field that this approach should be revised in order to overpass the problems related with these formulations, such as serotype replacement and high production costs. The study of conserved pneumococcal proteins or its truncated fragments has emerged as a serotype independent alternative. In this work, we have characterized the immune response elicited by systemic immunization of mice with the Histidine triad protein D (PhtD) and its' amino and carboxyl terminal fragments. The proteins were shown to be immunogenic and protective against pneumococcal colonization, with increased IL-17 production, and induction of antibodies able to limit pneumococcal adhesion to human respiratory cells. Antiserum against PhtD_Nter, but not C_ter or PhtD, promoted an increase in bacterial phagocytosis in vitro. Interestingly, antibodies against the PhtD_Nter displayed cross-reactivity with two other pneumococcal proteins, PspA and PspC, due to sequence similarities in the proline rich region of the molecules. On a whole, our results support the inclusion of PhtD, and more specifically, its N-terminal fragment, in a multicomponent serotype independent vaccine.

Introduction: About 30% of the patients healed from breast cancer recurred with metastasis, and the lymphatic is the main path of dissemination. Usually, postrenal acute kidney failure (AKI) is a result of gynecological, urological, gastrointestinal and retroperitoneal cancer, but unusual in breast cancer. Objectives: To report the unusual metastatic behavior of the carcinoma for diagnostic elucidation. Method: Anamnesis and review of medical charts and bibliography. Results: White, female, 69-year old women being retreated for invasive ductal breast cancer, luminal B type, was hospitalized in June, 2018, with hypothesis of bronchopneumonia and AKI due to dehydration and infection. Laboratory examinations indicated urea at 75 mg/dl, creatinine at 2.56 mg/dl, sodium at 141 mmol/L, and potassium at 4.2 mmol/L. The initial conduct included antibiotics and hydration with 0.9% saline solution. Abdominal and bladder ultrasound indicated dilatation of the pelvicalyceal systems system and proximal ureters, without pointing a location and cause of obstruction; urinary bladder with conserved shape and capacity; absence of images compatible with calculi and expansive solid, cystic or complex injuries. Due to the worsened glomerular filtration rate and oliguria, a double J catheter was inserted to the left. However, there was no improvement in kidney function. Then, a nephrostomy was performed to the right, which restituted urine traffic. In February, 2019, urotomography showed dilatation of the pelvicalyceal system and right ureters to the pelvis (L5), where it became narrow, with a 1.5 cm caliber ureter obstruction; multiple metastasis in the pelvic bones and bilateral pleural effusion. A double J catheter was inserted in the right ureter through a cateter via anterograde pathway, thus recovering kidney function and comfort. After 5 months, computed tomography showed pelvic lymphadenopathy as the cause of obstruction. Currently, the patient has a metallic catheter in the right side, with good general status and on anastrozole. Conclusions: Metastatic breast cancer is still challenging and prone to complications. Therefore, its knowledge allows a better approach of patients by correlating them with more diagnostic and care possibilities.