Promising strategies for future treatment of Klebsiella pneumoniae biofilms

Supernatant of platelet-Klebsiella pneumoniae coculture induces apoptosis-like death in Klebsiella pneumoniae

Multidrug-resistant Klebsiella pneumoniae strains, especially carbapenem-resistant K. pneumoniae, have become a rapidly emerging crisis worldwide, greatly limiting current therapeutic options and posing new challenges to infection management. Therefore, it is imperative to develop novel and effective biological agents for the treatment of multidrug-resistant K. pneumoniae infections. Platelets play an important role in the development of inflammation and immune responses. The main component responsible for platelet antibacterial activity lies in the supernatant stimulated by gram-positive bacteria. However, little research has been conducted on the interaction of gram-negative bacteria with platelets. Therefore, we aimed to explore the bacteriostatic effect of the supernatant derived from platelet-K. pneumoniae coculture and the mechanism underlying this effect to further assess the potential of platelet-bacterial coculture supernatant. We conducted this study on the gram-negative bacteria K. pneumoniae and CRKP and detected turbidity changes in K. pneumoniae and CRKP cultures when grown with platelet-K. pneumoniae coculture supernatant added to the culture medium. We found that platelet-K. pneumoniae coculture supernatant significantly inhibited the growth of K. pneumoniae and CRKP in vitro. Furthermore, transfusion of platelet-K. pneumoniae coculture supernatant alleviated the symptoms of K. pneumoniae and CRKP infection in a murine model. Additionally, we observed apoptosis-like changes, such as phosphatidylserine exposure, chromosome condensation, DNA fragmentation, and overproduction of reactive oxygen species in K. pneumoniae following treatment with the supernatant. Our study demonstrates that the platelet-K. pneumoniae coculture supernatant can inhibit K. pneumoniae growth by inducing an apoptosis-like death, which is important for the antibacterial strategies development in the future.IMPORTANCEWith the widespread use of antibiotics, bacterial resistance is increasing, and a variety of multi-drug resistant Gram-negative bacteria have emerged, which brings great challenges to the treatment of infections caused by Gram-negative bacteria. Therefore, finding new strategies to inhibit Gram-negative bacteria and even multi-drug- resistant Gram-negative bacteria is crucial for treating infections caused by Gram-negative bacteria, improving the abuse of antibiotics, and maintaining the balance between bacteria and antibiotics. K. pneumoniae is a common clinical pathogen, and drug-resistant CRKP is increasingly difficult to cure, which brings great clinical challenges. In this study, we found that the platelet-K. pneumoniae coculture supernatant can inhibit K. pneumoniae growth by inducing an apoptosis-like death. This finding has inspired the development of future antimicrobial strategies, which are expected to improve the clinical treatment of Gram-negative bacteria and control the development of multidrug-resistant strains.

Insights into the preventive actions of natural compounds against Klebsiella pneumoniae infections and drug resistance

Klebsiella pneumoniae is a type of Gram-negative bacteria that causes a variety of infections, including pneumonia, bloodstream infections, wound infections, and meningitis. The treatment of K. pneumoniae infection depends on the type of infection and the severity of the symptoms. Antibiotics are generally used to treat K. pneumoniae infections. However, some strains of K. pneumoniae have become resistant to antibiotics. This comprehensive review examines the potential of natural compounds as effective strategies against K. pneumonia infections. The alarming rise in antibiotic resistance underscores the urgent need for alternative therapies. This article represents current research on the effects of diverse natural compounds, highlighting their anti-microbial and antibiofilm properties against K. pneumonia. Notably, compounds such as andrographolide, artemisinin, baicalin, berberine, curcumin, epigallocatechin gallate, eugenol, mangiferin, piperine, quercetin, resveratrol, and thymol have been extensively investigated. These compounds exhibit multifaceted mechanisms, including disruption of bacterial biofilms, interference with virulence factors, and augmentation of antibiotic effectiveness. Mechanistic insights into their actions include membrane perturbation, oxidative stress induction, and altered gene expression. While promising, challenges such as limited bioavailability and varied efficacy across bacterial strains are addressed. This review further discusses the potential of natural compounds as better alternatives in combating K. pneumonia infection and emphasizes the need for continued research to harness their full therapeutic potential. As antibiotic resistance persists, these natural compounds offer a promising avenue in the fight against K. pneumonia and other multidrug-resistant pathogens.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

In vitro activity of novel apramycin-dextran nanoparticles and free apramycin against selected Dutch and Pakistani Klebsiella pneumonia isolates

Klebsiella pneumoniae are bacteria associated with respiratory tract infections and are increasingly becoming resistant to antibiotics, including carbapenems. Apramycin is a veterinary antibiotic that may have the potential to be re-purposed for use in human health, for example, for the treatment of respiratory tract infections after coupling to inhalable nanoparticles. In the present study, the antibiotic apramycin was formulated with single chain polymeric nanoparticles and tested in free and formulated forms against a set of 13 Klebsiella pneumoniae isolates (from the Netherlands and Pakistan) expressing different aminoglycoside resistance phenotypes. Minimum Inhibitory Concentration, Time Kill Kinetics and biofilm experiments were performed providing evidence for the potential efficacy of apramycin and apramycin-based nanomedicines for the treatment of human Klebsiella pneumonia infections.

Klebsiella phage KP34gp57 capsular depolymerase structure and function: from a serendipitous finding to the design of active mini-enzymes against K. pneumoniae

IMPORTANCE

In this work, we determined the structure of Klebsiella phage KP34p57 capsular depolymerase and dissected the role of individual domains in trimerization and functional activity. The crystal structure serendipitously revealed that the enzyme can exist in a monomeric state once deprived of its C-terminal domain. Based on the crystal structure and site-directed mutagenesis, we localized the key catalytic residues in an intra-subunit deep groove. Consistently, we show that C-terminally trimmed KP34p57 variants are monomeric, stable, and fully active. The elaboration of monomeric, fully active phage depolymerases is innovative in the field, as no previous example exists. Indeed, mini phage depolymerases can be combined in chimeric enzymes to extend their activity ranges, allowing their use against multiple serotypes.

Detection and Quantification of Klebsiella pneumoniae in Fecal Samples Using Digital Droplet PCR in Comparison with Real-Time PCR

This study aimed to develop a rapid and sensitive droplet digital PCR (ddPCR) assay for the specific detection of Klebsiella pneumoniae in fecal samples, and to evaluate its application in the clinic by comparison with real-time PCR assay and conventional microbial culture. Specific primers and a probe targeting the K. pneumoniae hemolysin (khe) gene were designed. Thirteen other pathogens were used to evaluate the specificity of the primers and probe. A recombinant plasmid containing the khe gene was constructed and used to assess the sensitivity, repeatability, and reproducibility of the ddPCR. Clinical fecal samples (n = 103) were collected and tested by the ddPCR, real-time PCR, and conventional microbial culture methods. The detection limit of ddPCR for K. pneumoniae was 1.1 copies/μL, about a 10-fold increase in sensitivity compared with real-time PCR. The ddPCR was negative for the 13 pathogens other than K. pneumoniae, confirming its high specificity. Clinical fecal samples gave a higher rate of positivity in the K. pneumoniae ddPCR assay than in analysis by real-time PCR or conventional culture. ddPCR also showed less inhibition by the inhibitor in fecal sample than real-time PCR. Thus, we established a sensitive and effective ddPCR-based assay method for K. pneumoniae. It could be a useful tool for K. pneumoniae detection in feces and may serve as a reliable method to identify causal pathogens and help guide treatment decisions. IMPORTANCE Klebsiella pneumoniae can cause a range of illnesses and has a high colonization rate in the human gut, making it crucial to develop an efficient method for detecting K. pneumoniae in fecal samples.

1,25(OH)2D3 promotes the elimination of Klebsiella pneumoniae infection by inducing autophagy through the VDR-ATG16L1 pathway

OBJECTIVE

Previous studies have shown that vitamin D has regulatory functions in both innate and adaptive immune responses, indicating that it can perform essential roles in host resistance to pathogen infections. This study aimed to verify its effects on Klebsiella pneumoniae (Kp) infection and explore the underlying mechanisms.

METHODS

THP-1-derived macrophages were infected with Kp and then incubated with 1,25(OH)₂D₃. Autophagy induced by 1,25(OH)₂D₃ was investigated by western blotting and immunofluorescence. Real-time PCR (qPCR) was performed to determine the expression of inflammatory mediators. Baf A1 and 3-MA were used to inhibit autophagy. The intracellular killing of Kp was measured using qPCR and colony-forming unit assays. RNA interference assays were used to silence VDR or ATG16L1. The lungs of C57BL/6 mice were infected with Kp via intratracheal instillation, and the established pneumonia models were used for in vivo validation experiments.

RESULTS

Treatment with 1,25(OH)₂D₃ enhanced the bactericidal activity of macrophages and concomitantly reduced the expression of the pro-inflammatory mediators TNF-α and IL-6. Kp infection led to a lower expression level of VDR in macrophages than in the control, whereas co-treatment with 1,25(OH)₂D₃ up-regulated VDR expression and robustly induced autophagy via the VDR signaling pathway. Silencing ATG16L1 significantly counteracted autophagy induced by 1,25(OH)₂D₃ in Kp-infected macrophages. Furthermore, we found that when autophagy activity was diminished by ATG16L1 siRNA or blocked by Baf A1, the ability of 1,25(OH)₂D₃ to promote macrophages to eliminate Kp infection was obviously impaired, as were its anti-inflammatory effects. These protective efficacies of 1,25(OH)₂D₃ against Kp infection were also validated in vivo using a mouse model of pneumonia.

CONCLUSIONS

The present study demonstrated the protective features of 1,25(OH)₂D₃ in macrophages against Kp infection and may provide evidence for further exploration of its potential as an adjunctive therapy agent for the treatment of bacterial infections.

Antibiofilm Synergistic Activity of Streptomycin in Combination with Thymol-Loaded Poly (Lactic-co-glycolic Acid) Nanoparticles against Klebsiella pneumoniae Isolates

Background. Thymol is an important component of essential oils found in the oil of thyme, is extracted mainly from Thymus vulgaris, and was shown to act synergistically with streptomycin against Klebsiella pneumoniae biofilms. Additionally, thymol could be encapsulated into poly (lactic-co-glycolic acid) (PLGA) nanoparticles to overcome issues related to its low water solubility and high volatility. The present study aimed to investigate the antibiofilm activity of thymol-loaded PLGA nanoparticles (Thy-NPs) alone and in combination with streptomycin against biofilms of K. pneumoniae isolates. Methods. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The antibiofilm activities were determined by the safranin dye assay. The synergistic effect of Thy-NPs with streptomycin was assessed by the checkerboard method. The kinetic study of the biofilm biomass and time-kill assay were further performed. Results. Thy-NPs exhibited the highest antibacterial activity against K. pneumoniae isolates, with MIC values ranging from 1 to 8 µg/mL. Additionally, Thy-NPs showed the highest antibiofilm activity against K. pneumoniae isolates with minimal biofilm inhibitory concentration (MBIC) and minimal biofilm eradication concentration (MBEC) values ranging from 16 to 64 µg/mL and from 32 to 128 µg/Ml, respectively. The combination treatment combining Thy-NPs with streptomycin showed a synergistic effect against the inhibition of biofilm formation and eradication of biofilms of K. pneumoniae isolates with fractional inhibitory concentration index values ranging from 0.13 to 0.28. In addition, the MBIC and MBEC values of streptomycin against K. pneumoniae isolates were dramatically reduced (up to 128-fold) in combination with Thy-NPs, suggesting that Thy-NPs would enhance the antibiofilm activity of streptomycin. The biomass and time-kill kinetics analysis confirmed the observed synergistic interactions and showed the bactericidal activity of streptomycin in combination with Thy-NPs. Conclusions. Our results indicate that the synergistic bactericidal effect between streptomycin and Thy-NPs could be a promising approach in the control of biofilm-associated infections caused by K. pneumoniae.

Antibiotic resistant bacteria: current situation and treatment options to accelerate the development of a new antimicrobial arsenal

INTRODUCTION

Antibiotic resistance is one of the biggest public health threats worldwide. Currently, antibiotic-resistant bacteria kill 700,000 people every year. These data represent the near future in which we find ourselves, a "post-antibiotic era" where the identification and development of new treatments are key. This review is focused on the current and emerging antimicrobial therapies which can solve this global threat.

AREAS COVERED

Through a literature search using databases such as Medline and Web of Science, and search engines such as Google Scholar, different antimicrobial therapies were analyzed, including pathogen-oriented therapy, phagotherapy, microbiota and antivirulent therapy. Additionally, the development pathways of new antibiotics were described, emphasizing on the potential advantages that the combination of a drug repurposing strategy with the application of mathematical prediction models could bring to solve the problem of AMRs.

EXPERT OPINION

This review offers several starting points to solve a single problem: reducing the number of AMR. The data suggest that the strategies described could provide many benefits to improve antimicrobial treatments. However, the development of new antimicrobials remains necessary. Drug repurposing, with the application of mathematical prediction models, is considered to be of interest due to its rapid and effective potential to increase the current therapeutic arsenal.

Virulence Genotype and Correlation of Clinical Severeness with Presence of the Type VI Secretion System in Klebsiella pneumoniae Isolates Causing Bloodstream Infections

Background

Klebsiella pneumoniae (K. pneumoniae) causes bloodstream infection (BSI), which is responsible for a high rate of morbidity and mortality among different populations. In mainland China, data on the correlation and features of the type VI secretion system (T6SS) gene cluster in K. pneumoniae is currently scarce. As a result, we conducted a prospective investigation to determine the involvement of the T6SS in K. pneumoniae pathogenicity and antibiotic resistance.

Methods

In this prospective analysis, we enrolled 119 individuals who had been diagnosed with K. pneumoniae bloodstream infection between July 2019 and January 2021 and acquired demographic and clinical data from their medical records. The virulence genes rmpA, rmpA2, aerobactin, iroB, hcp, vgrG, and icmF were tested for K1 and K2, antimicrobial susceptibility. Five T6SS-positive and five T6SS-negative isolates were chosen for the competition, serum resistance, and biofilm formation experiments to further gain insights regarding the microbiological properties of T6SS-positive K. pneumoniae isolates.

Results

Among 119 isolates obtained from patients with BSIs, 20 (16.8%) were T6SS positive K. pneumoniae. T6SS positive strains had four virulence genes and a greater K1 capsular serotypes rate than T6SS negative bacteria. Among hvKP isolates, the T6SS positive rate was substantially greater than the T6SS negative rate (P = 0.001). T6SS-positive K. pneumoniae strains had a lower rate of antimicrobial resistance in comparison to T6SS-negative bacteria. T6SS-positive isolates may be more competitive with Escherichia coli than T6SS-negative isolates. T6SS-positive isolates, on the other hand, did not show stronger biofilm-forming activity or a higher survival rate in the presence of normal human serum in comparison to T6SS-negative isolates.

Conclusion

T6SS-positive K. pneumoniae was common in people who had BSIs. In T6SS‐containing K. pneumoniae, the system may play a major role in bacterial competition.

Molecular Epidemiology of Hypervirulent K. pneumoniae and Problems of Health-Care Associated Infections

The review describes virulence factors of hypervirulent K. pneumoniae (hvKp) including genes determining its virulence and discusses their role in the development of health-care associated infections. The contribution of individual virulence factors and their combination to the development of the hypervirulence and the prospects of using these factors as biomarkers and therapeutic targets are described. Virulence factors of hvKp and “classical” K. pneumoniae strains (cKp) with no hypervirulence genes were compared. The mechanisms of biofilm formation by hvKp and high incidence of its antibiotic resistance are of particular importance for in health care institutions. Therefore, the development of methods for hvKp identification allowing early prevention of severe hvKp infection and novel approaches to abrogate its spreading are new challenges for epidemiology, infection diseases, and critical care medicine. New technologies including bacteriological and molecular studies make it possible to develop innovative strategies to diagnose and treat infection caused by hvKp. These include monitoring of both genetic biomarkers of hvKp and resistance plasmid that carry of virulence genes and antibiotic resistance genes, creation of immunological agents for the prevention and therapy of hvKp (vaccines, monoclonal antibodies) as well as personalized hvKp-specific phage therapies and pharmaceuticals enhancing the effect of antibiotics. A variety of approaches can reliably prepare our medicine for a new challenge: spreading of life-threatening health-care associated infections caused by antibiotic-resistant hvKp strains.

The Association of the Phylogenetic Typing of the Klebsiella pneumoniae Isolates with Antibiotic Resistance

Klebsiella pneumoniae complex (KPC) accounts for approximately one-third of all Gram-negative infections. Moreover, it is highly resistant and can taxonomically be distributed into KpI, KpII, and KpIII phylogroups. This study aimed to investigate the distribution of phylogenetic groups and the relationship between them and antibiotic resistance patterns. For this purpose, we collected KPC isolates from Tabriz, Iran, between 2018 and 2020. Antimicrobial susceptibility testing was performed by disk diffusion agar, and phylogenetic groups were then examined using gyrA restriction fragment length polymorphism (RFLP) and parC PCR methods. A total of 100 KPC isolates were obtained from the clinical specimens (urine, respiratory secretion, blood, wounds, and trachea). The enrolled patients included 47 men and 53 women aged from 1 to 91 years old. The highest sensitivity was found related to fosfomycin as 85%, followed by amikacin as 66%. The three phylogenetically groups by the RFLP-PCR method were found in KPC, 96% (96 isolates) as KpI, 3% (3 isolates) as KpII, and 1% (1isolate) as KpIII. The highest antibiotic resistance was observed in KpI. It was shown that a valid identification of three phylogenetic groups of KPC can be done by combining both gyrA PCR-RFLP and parC PCR. Of note, the KpI group was also observed as the dominant phylogenetic group with the highest resistance to antibiotics.

Synergistic Antibiofilm Efficacy of Thymol and Piperine in Combination with Three Aminoglycoside Antibiotics against Klebsiella pneumoniae Biofilms

BACKGROUND

Thymol and piperine are two naturally occurring bioactive compounds with several pharmacological activities. In this study, their antibiofilm potential either alone or in combination with three aminoglycoside antibiotics was evaluated against a biofilm of Klebsiella pneumoniae.

METHODS

Determination of antimicrobial susceptibility was performed using the broth microdilution method. Biofilm formation was evaluated by the microtiter plate method. Antibiofilm activity was determined using 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium-bromide (MTT) assay. The combination studies were performed by the checkerboard microdilution method.

RESULTS

The minimum biofilm inhibitory concentration (MBIC) of streptomycin was reduced by 16- to 64-fold when used in combination with thymol, while the MBIC of kanamycin was reduced by 4-fold when combined with piperine. The minimum biofilm eradication concentration (MBEC) values of streptomycin, amikacin, and kanamycin were, respectively, 16- to 128-fold, 4- to 128-fold, and 8- to 256-fold higher than the planktonic minimum inhibitory concentration (MIC). Thymol combined with streptomycin or kanamycin showed synergic effects against the preformed biofilm with 16- to 64-fold reduction in the minimum biofilm eradication concentration values of each antibiotic in combination. Piperine acted also synergically with kanamycin with an 8- to 16-fold reduction in the minimum biofilm eradication concentration values of kanamycin in combination.

CONCLUSION

The association of thymol with antibiotics showed a strong synergistic effect both in the inhibition of biofilm formation and the destruction of the preformed biofilm of K. pneumoniae. This study suggests that a combination of thymol with streptomycin, amikacin, or kanamycin could be a promising alternative therapy to overcome the problem of K. pneumoniae biofilm-associated infections.

Antibacterial, anti-efflux, anti-biofilm, anti-slime (exopolysaccharide) production and urease inhibitory efficacies of novel synthesized gold nanoparticles coated Anthemis atropatana extract against multidrug- resistant Klebsiella pneumoniae strains

In this study, the antibacterial, anti-efflux, anti-biofilm, anti-slime (exopolysaccharide) production and urease inhibitory efficacies of green synthesized gold nanoparticles (AuNPs) coated Anthemis atropatana extract against multidrug- resistant (MDR) Klebsiella pneumoniae strains were evaluated. The green synthesized AuNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometer (XRD), particle size distribution, zeta potential and Fourier-transform infrared spectroscopy (FTIR). Then, antibacterial, anti-slime (exopolysaccharide) production, anti-biofilm and anti-efflux activities of AuNPs were investigated using micro-dilation, Congored agar, microtiter plate and MIC of ethidium bromide methods, respectively. Subsequently, the expression of mrkA, wzm and acrB genes was evaluated using quantitative Real-Time PCR (qRT-PCR). The synthesized AuNPs exhibited antibacterial activity against MDR strains of K. pneumoniae (minimum inhibitory concentration (MIC) of 6.25-50 µg/ml), as well as showed significant anti-slime (exopolysaccharide) production, anti-biofilm and anti-efflux activities against MDR strains. AuNPs showed significant inhibition against jack-bean urease and down-regulated the expression of mrkA, wzm and acrB genes. Moreover, the in vitro cytotoxic activity confirmed by MTT assay on the HEK-293 normal cell line showed negligible cytotoxicity. Thus, the present study suggests the potential use of AuNPs in the development of novel therapeutics for the prevention of biofilm-associated K. pneumoniae infections.