Innate Host Defense against Klebsiella pneumoniae and the Outlook for Development of Immunotherapies

Vaccine value profile for Klebsiella pneumoniae

Klebsiella pneumoniae causes community- and healthcare-associated infections in children and adults. Globally in 2019, an estimated 1.27 million (95% Uncertainty Interval [UI]: 0.91-1.71) and 4.95 million (95% UI: 3.62-6.57) deaths were attributed to and associated with bacterial antimicrobial resistance (AMR), respectively. K. pneumoniae was the second leading pathogen in deaths attributed to AMR resistant bacteria. Furthermore, the rise of antimicrobial resistance in both community- and hospital-acquired infections is a concern for neonates and infants who are at high risk for invasive bacterial disease. There is a limited antibiotic pipeline for new antibiotics to treat multidrug resistant infections, and vaccines targeted against K. pneumoniae are considered to be of priority by the World Health Organization. Vaccination of pregnant women against K. pneumoniae could reduce the risk of invasive K.pneumoniae disease in their young offspring. In addition, vulnerable children, adolescents and adult populations at risk of K. pneumoniae disease with underlying diseases such as immunosuppression from underlying hematologic malignancy, chemotherapy, patients undergoing abdominal and/or urinary surgical procedures, or prolonged intensive care management are also potential target groups for a K. pneumoniae vaccine. A 'Vaccine Value Profile' (VVP) for K.pneumoniae, which contemplates vaccination of pregnant women to protect their babies from birth through to at least three months of age and other high-risk populations, provides a high-level, holistic assessment of the available information to inform the potential public health, economic and societal value of a pipeline of K. pneumoniae vaccines and other preventatives and therapeutics. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, public-private partnerships, and multi-lateral organizations, and in collaboration with stakeholders from the WHO. All contributors have extensive expertise on various elements of the K.pneumoniae VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

Immunostimulatory chimeric protein encapsulated in gelatin nanoparticles elicits protective immunity against Pseudomonas aeruginosa respiratory tract infection

This study presents the design and fabrication of an innovative vaccine candidate targeting Pseudomonas aeruginosa (P. aeruginosa). The vaccine consists of gelatin nanoparticles (GNPs) encapsulating a chimeric protein (CP) derived from the ExoS and OprI proteins from P. aeruginosa. The physicochemical properties of the GNPs were assessed using dynamic light scattering (DLS) and electron microscopy. The toxicity, encapsulation efficacy, release profile, and effectiveness of CP-encapsulated GNPs (CP-GNPs) in an animal model were investigated. The resulting nanovaccine demonstrated uniform spherical particles with an average size of 135 nm and an encapsulation efficiency of 85 %. The release assay revealed that 23 % of the antigen was released from the CP-GNPs after 20 days. The GNPs did not exhibit any toxic effects on L929 cells in vitro. The formulation induced both systemic and mucosal antibody responses. Additionally, CP-GNPs stimulated cytokine responses, including IFN-γ, IL-4, and IL-17, indicating the induction of both humoral (Th2) and cellular (Th1) responses. The CP-encapsulated GNPs formulation effectively protected the mice lungs against experimental respiratory tract infection, reducing colony count and inflammation. These findings suggest that CP-GNPs hold promise as a potential strategy for preventing respiratory tract infections caused by P. aeruginosa. Further research is needed to explore its clinical application.

Interactions and Implications of Klebsiella pneumoniae with Human Immune Responses and Metabolic Pathways: A Comprehensive Review

Klebsiella pneumoniae (K. pneumoniae), a significant contributor to the global challenge of antibiotic resistance, is not only a ubiquitous component of the human microbiome but also a potent pathogen capable of causing a spectrum of diseases. This review provides a thorough analysis of the intricate interactions between K. pneumoniae and the human immune system, elucidating its substantial impact on metabolic processes. We explore the mechanisms employed by K. pneumoniae to evade and manipulate immune responses, including molecular mimicry, immune modulation, and biofilm formation. The review further investigates the bacterium's influence on metabolic pathways, particularly glycolysis, highlighting how these interactions exacerbate disease severity. The emergence of multidrug-resistant and extremely drug-resistant strains within the Enterobacteriaceae family has heightened the public health crisis, underscoring the urgency for comprehensive research. We investigate the roles of the host's complement system, autophagy, cell death mechanisms, and various cytokines in combating K. pneumoniae infections, shedding light on areas that warrant further academic investigation. Additionally, the review discusses the challenges posed by K1- and K2-capsule polysaccharides in vaccine development due to their complex molecular structures and adhesive properties. Acknowledging the limited availability of effective antimicrobials, this review advocates for exploring alternative approaches such as immunotherapeutics, vaccinations, and phage therapy. We consolidate current knowledge on K. pneumoniae, covering classical and non-classical subtypes, antimicrobial resistance-mediated genes, virulence factors, and epidemiological trends in isolation and antibiotic resistance rates. This comprehensive review not only advances our understanding of K. pneumoniae but also underscores the imperative for ongoing research and collaborative efforts to develop new prevention and treatment strategies against this formidable pathogen.

Design and fabrication of a vaccine candidate based on rOmpA from Klebsiella pneumoniae encapsulated in silk fibroin-sodium alginate nanoparticles against pneumonia infection

The present study describes the design and fabrication of a novel vaccine candidate based on the outer membrane protein A (rOmpA) from Klebsiella pneumoniae (K. pneumoniae) encapsulated in silk fibroin-sodium alginate nanoparticles (SF-SANPs) against K. pneumoniae-mediated pneumonia. The physicochemical properties, toxicity, release profile, and in vivo potency of SF-SANPs encapsulated with rOmpA were evaluated. The spherical nano vaccine was created with an average particle size of 160 nm and an encapsulation efficiency of 80 %. Antigen release from SF-SANPs was 40 % after 22 days release assay. The SF-SANPs showed a zeta potential of -24.8 mV and had no toxic effect on the L929 cells in vitro. It was found that SF-SANPs in the vaccine formulation promoted systemic and mucosal antibodies and also stimulated cytokine responses, inducing both humoral (Th2) and cellular (Th1) immune responses, with a Th1-polarized response. The vaccine candidate was effective in protecting the mice lung against experimental pneumonia and reducing inflammation. These findings suggest that the rOmpA-based vaccine encapsulated in SF-SANPs could be a promising strategy for preventing pneumonia caused by K. pneumoniae.

The Type VI Secretion System Contributes to the Invasiveness of Liver Abscess Caused by Klebsiella pneumoniae

BACKGROUND

Klebsiella pneumoniae liver abscess (KPLA) with extrahepatic migratory infections is defined as invasive KPLA (IKPLA). The type VI secretion system (T6SS) is involved in the pathogenesis of KPLA. We hypothesized that T6SS plays a role in IKPLA.

METHODS

16S ribosomal RNA gene sequencing was performed on abscess samples. Polymerase chain reaction (PCR) and reverse-transcription PCR (RT-PCR) was used to validate the expression difference of T6SS hallmark genes. In vitro and in vivo experiments were performed to identify the pathogenic feature of T6SS.

RESULTS

PICRUSt2 predicted that the T6SS-related genes were notably enriched in the IKPLA group. PCR detection of T6SS hallmark genes (hcp, vgrG, and icmF) showed that 197 (81.1%) were T6SS-positive strains. The T6SS-positive strain detection rate in the IKPLA group was higher than in the KPLA group (97.1% vs 78.4%; P < .05). RT-PCR showed that the hcp expression level was markedly increased in IKPLA isolates (P < .05). The T6SS-positive isolates showed higher survival against serum and neutrophil killing (all P < .05). The T6SS-positive K pneumoniae-infected mice had a shorter survival time, higher mortality, and an increased interleukin 6 expression in the liver and lungs (all P < .05).

CONCLUSIONS

T6SS is an essential virulence factor for K pneumoniae and contributes to IKPLA.

Klebsiella pneumoniae: adaptive immune landscapes and vaccine horizons

Klebsiella pneumoniae is among the most common antibiotic-resistant pathogens causing nosocomial infections. Additionally, it is a leading cause of neonatal sepsis and childhood mortality across the globe. Despite its clinical importance, we are only beginning to understand how the mammalian adaptive immune system responds to this pathogen. Further, many studies investigating potential K. pneumoniae vaccine candidates or alternative therapies have been launched in recent years. Here, we review the current state of knowledge on the adaptive immune response to K. pneumoniae infections and progress towards developing vaccines and other therapies to combat these infections.

Clinical and Molecular Characteristics and Antibacterial Strategies of Klebsiella pneumoniae in Pyogenic Infection

Treatment of Klebsiella pneumoniae causing pyogenic infections is challenging. The clinical and molecular characteristics of Klebsiella pneumoniae causing pyogenic infections are poorly understood, and antibacterial treatment strategies are limited. We analyzed the clinical and molecular characteristics of K. pneumoniae from patients with pyogenic infections and used time-kill assays to reveal the bactericidal kinetics of antimicrobial agents against hypervirulent K. pneumoniae (hvKp). A total of 54 K. pneumoniae isolates were included, comprising 33 hvKp and 21 classic K. pneumoniae (cKp) isolates, and the hvKp and cKp isolates were identified using five genes (iroB, iucA, rmpA, rmpA2, and peg-344) that have been applied as hvKp strain markers. The median age of all cases was 54 years (25th and 75th percentiles, 50.5 to 70), 62.96% of individuals had diabetes, and 22.22% of isolates were sourced from individuals without underlying disease. The ratios of white blood cells/procalcitonin and C-reactive protein/procalcitonin were potential clinical markers for the identification of suppurative infection caused by hvKp and cKp. The 54 K. pneumoniae isolates were classified into 8 sequence type 11 (ST11) and 46 non-ST11 strains. ST11 strains carrying multiple drug resistance genes have a multidrug resistance phenotype, while non-ST11 strains carrying only intrinsic resistance genes are generally susceptible to antibiotics. Bactericidal kinetics revealed that hvKp isolates were not easily killed by antimicrobials at susceptible breakpoint concentrations compared with cKp. Given the varied clinical and molecular features and the catastrophic pathogenicity of K. pneumoniae, it is critical to determine the characteristics of such isolates for optimal management and effective treatment of K. pneumoniae causing pyogenic infections. IMPORTANCE Klebsiella pneumoniae may cause pyogenic infections, which are potentially life-threatening and bring great challenges for clinical management. However, the clinical and molecular characteristics of K. pneumoniae are poorly understood, and effective antibacterial treatment strategies are limited. We analyzed the clinical and molecular features of 54 isolates from patients with various pyogenic infections. We found that most patients with pyogenic infections had underlying diseases, such as diabetes. The ratio of white blood cells to procalcitonin and the ratio of C-reactive protein to procalcitonin were potential clinical markers for differentiating hypervirulent K. pneumoniae strains from classical K. pneumoniae strains that cause pyogenic infections. K. pneumoniae isolates of ST11 were generally more resistant to antibiotics than non-ST11 isolates. Most importantly, hypervirulent K. pneumoniae strains were more tolerant to antibiotics than classic K. pneumoniae isolates.

Challenges in development of vaccines directed toward antimicrobial resistant bacterial species

Antimicrobial resistance (AMR) is considered by WHO one of the top ten public health threats. New control strategies involving concerted actions of both public and private sectors need to be developed. Vaccines play a major role in controlling the spread of AMR pathogens by decreasing transmission and limiting the use of antibiotics, reducing at the end the selective pressure for the emergence of new resistant strains. In this review, by using as example some of the most serious AMR pathogens, we highlighted the major hurdles from a research and development point of view. New approaches to better understand the immunological mechanisms of response to both natural infections and vaccines that aimed to identify correlates of protection, together with the application of new technologies for vaccine design and delivery are discussed as potential solutions.

Finding epitopes of Klebsiella pneumoniae outer membrane protein-K17 (OMPK17) and introducing a 25-mer peptide of it as a vaccine candidate

No approved vaccine exists for Klebsiella pneumoniae yet. Outer membrane protein-K17 (OMPK17) is involved in K. pneumoniae pathogenesis. No information has been found about OMPK17 dominant epitopes in the literature. Therefore, this study aimed to predict both T cell and B cell epitopes of K. pneumoniae OMPK17 via immunoinformatics approaches. Both T cell (class-I and II) and B cell (linear and discontinuous) epitopes of OMPK17 were predicted. Several screening analyses were performed including clustering, immunogenicity, human similarity, toxicity, allergenicity, conservancy, docking, and structural/physicochemical suitability. The results showed that some regions of OMPK17 have more potential as epitopes. The most possible epitopes were found via several analyses including the selection of higher-scoring epitopes, the epitopes predicted with more tools, more immunogenic epitopes, the epitopes capable of producing interferon-gamma, the epitopes with more dissimilarity to human peptides, and non-toxic and non-allergenic epitopes. By comparing the best T cell and B cell epitopes, we reached a 25-mer peptide containing both T cell (class-I and class-II) and B cell (linear) epitopes and comprising appropriate physicochemical characteristics that are required for K. pneumoniae vaccine development. The in vitro/in vivo study of this peptide is recommended to clarify its actual efficiency and efficacy.

Supplementary information

The online version contains supplementary material available at 10.1007/s11756-023-01371-0.

Host defense against the infection of Klebsiella pneumoniae: New strategy to kill the bacterium in the era of antibiotics?

Klebsiella pneumoniae (K. pneumoniae) is a typical gram-negative iatrogenic bacterium that often causes bacteremia, pneumonia and urinary tract infection particularly among those with low immunity. Although antibiotics is the cornerstone of anti-infections, the clinical efficacy of β-lactamase and carbapenems drugs has been weakened due to the emergence of drug-resistant K. pneumoniae. Recent studies have demonstrated that host defense plays a critical role in killing K. pneumoniae. Here, we summarize our current understanding of host immunity mechanisms against K. pneumoniae, including mechanical barrier, innate immune cells, cellular immunity and humoral immunity, providing a theoretical basis and the new strategy for the clinical treatment of K. pneumoniae through improving host immunity.

Phenotypic Characterization of Virulence Factors and Antibiogram of Klebsiella pneumoniae Isolates from Various Clinical Samples – A Cross Sectional Study

K. pneumoniae is known to cause hospital and community acquired infections. It is usually associated with upper & lower respiratory infections, septicaemia, urinary tract infection, wound infections, neonatal sepsis, meningitis, and endophthalmitis. The virulence factors play a role in its existence in different environmental conditions and therefore help in establishing Klebsiella pneumoniae infection in the human body. Multi drug resistant Klebsiella pneumoniae is an increasing threat to human health. Klebsiella pneumoniae is one of the species recognized as nosocomial pathogens that exhibit multidrug resistance and virulence in ESKAPE group as per WHO. The study was conducted to determine the various virulence factors & the antimicrobial pattern of Klebsiella pneumoniae isolates. A cross sectional observational study, conducted in Department of Microbiology of R.L. Jalappa Hospital and Research Centre, Kolar, Sample size of 150. All 150 Klebsiella pneumoniae isolates collected for the study, The Klebsiella pneumoniae isolates which were positive for various virulence factors were as follows on hemolysis 7(4.66%), capsule 150(100%), Hypermucoviscosity formation 66(44%), biofilm production 81(54%), siderophore production 110(73.33%), protease 135(90%), gelatinase 126(84%), lipase production 119(79.33%), lecithinase activity 82(54.66%). The drug resistance klebsiella pneumoniae were as follows: ESBL producers 24(16.67%), AmpC producers were 22(14.67%), MDR 116(74.20%), extensive drug resistant (XDR) 30(20%), pan drug resistant (PDR) 42(28%), Carbapenem resistance 65.33% reported. The increasing coexistence of virulence factors & antimicrobial resistance pattern is of particular concern. Hence active surveillance for antimicrobial resistance & virulence determinants is imperative now to implement effective control measures to prevent the rapid spread of drug resistance.

Prevalence of hypervirulent and carbapenem-resistant Klebsiella pneumoniae under divergent evolutionary patterns

K1/K2 hvKP strains acquire carbapenem-resistance plasmids, known as CR-hvKp, and carbapenem-resistant Klebsiella pneumoniae (CRKP) strains obtain virulence plasmids, recognized as hv-CRKP. The two different evolution patterns of hypervirulent combined carbapenem-resistant Klebsiella pneumoniae may lead to their different prevalence in hospitals. Our study aimed to investigate the prevalence of hv-CRKP and CR-hvKp strains and to analyze factors influencing their evolution and prevalence. We collected 890 K. pneumoniae genomes from GenBank and 530 clinical K. pneumoniae isolates from nine hospitals. Our study found that hv-CRKP strains were more prevalent than CR-hvKp strains and both were dominated by bla_KPC-2 gene. The bla_KPC-2-carrying plasmids could mobilize non-conjugative virulence plasmids from hvKp strains to CRKP strains. The conserved oriT of virulence plasmids and the widespread of conjugative helper plasmids were potential factors for the mobilization of non-conjugative virulence plasmids. HvKp strains with KPC plasmid could hardly simultaneously exhibit hypervirulence and carbapenem resistance as CRKP strains with virulence plasmid, and we found that rfaH mutation reduced capsular synthesis and increased carbapenem resistance of the CR-hvKp strain. In summary, this study revealed that hv-CRKP strains were more suitable for survival in hospital settings than CR-hvKp strains and the widespread conjugative KPC-producing plasmids contributed to the emergence and prevalence of hv-CRKP strains.

A New Live Auxotrophic Vaccine Induces Cross-Protection against Klebsiella pneumoniae Infections in Mice

The development of a whole-cell vaccine from bacteria auxotrophic for D-amino acids present in the bacterial cell wall is considered a promising strategy for providing protection against bacterial infections. Here, we constructed a prototype vaccine, consisting of a glutamate racemase-deficient mutant, for preventing Klebsiella pneumoniae infections. The deletion mutant lacks the murI gene and requires exogenous addition of D-glutamate for growth. The results showed that the K. pneumoniae ΔmurI strain is attenuated and includes a favourable combination of antigens for inducing a robust immune response and conferring an adequate level of cross-protection against systemic infections caused by K. pneumoniae strains, including some hypervirulent serotypes with elevated production of capsule polysaccharide as well as multiresistant K. pneumoniae strains. The auxotroph also induced specific production of IL-17A and IFN-γ. The rapid elimination of the strain from the blood of mice without causing disease suggests a high level of safety for administration as a vaccine.